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ND Isotopes: Investigation of Cretaceous Ocean Anoxic Event 2 and a Systematic Study of Fe-Mn Oxide Coatings


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ND ISOTOPES: INVESTIGATION OF CRETACE OUS OCEAN ANOXIC EVENT 2 AND A SYSTEMATIC STUDY OF FE-MN OXIDE COATINGS By SUSANNA WHITMAN BLAIR A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Susanna Whitman Blair

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This document is dedicated to Dr. Mary K. Blair and Dr. Blair Plimpton.

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iv ACKNOWLEDGMENTS I would first like to sincerely thank Dr. Ellen Mart in for her continued help and guidance on this project. Though there were a number of challenges and setbacks, she was always persistent and positive about th e progress. She is not only a wonderful advisor and mentor but a dear friend and confidant. I will undoubtedly miss he r. Thanks go also to my committee members Dr. Paul Mueller and Dr. Philip Neuhoff for their advice and review of this thesis. I am also very grateful for the financia l support that was provided by the NSF SGR grant awarded to Dr. Ellen Martin. Special acknowledgements go to Dr. Ge orge Kamenov for his patience and continuous help. This project would not ha ve been completed without his guidance, suggestions, laboratory help, and assistance with analys is equipment. He is a true asset to this department and I was very lucky to have worked with him. Thanks go also to Dr. Ann Heatherington for her assistance with the TIMS. Thanks also go to Ken MacLeod for his help with the OAE por tion of this project. An appreciative thank you goes to Dr. Howa rd Scher for his guidance and help in the laboratory at a very early stage. He was definitely the force behind the start of this project and a number of the ear ly analysis. I would also like to thank Derrrick Newkirk and the many others who have helped me in the laboratory. Finally, I would like to thank my family and friends. Thanks go to Mary Blair for her unfaltering love and support. She is my dearest friend. Thanks go to Blair Plimpton

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v for being the first geologist in the family. Thanks go to David Sutton for his love and neverending encouragement. Thanks go to my many wonderf ul friends in the Department of Geological Science at UF, es pecially to Jillian Hinds, Gillian Rosen, Warren Grice, Derrick Newkirk, Jane Gu stavson, and Kelly McGowan for their friendship and laughter. Thanks go to Dr Karen Harpp for her encouragement to continue on to graduate school. And last but not least thanks go to my many wonderful friends from Colgate University and from Baltimore, especially Miranda Clark for reading the following.

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vi TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...........................................................................................................viii LIST OF FIGURES...........................................................................................................ix ABSTRACT....................................................................................................................... xi CHAPTER 1 INTRODUCTION........................................................................................................1 2 GENERAL BACKGROUND......................................................................................6 2.1 Isotope Systematics................................................................................................6 2.1.1 Neodymium..................................................................................................6 2.1.2 Strontium.....................................................................................................8 2.1.3 Carbon..........................................................................................................9 2.2 General Ocean Circulation...................................................................................10 2.3 Archives of Nd isotopes........................................................................................11 2.4 Description of Sample Sites..................................................................................16 2.4.1 DSDP Site 608............................................................................................16 2.4.2 ODP Site 647..............................................................................................17 2.4.3 ODP Site 689..............................................................................................18 2.4.4 ODP site 690...............................................................................................18 2.4.5 ODP Site 886..............................................................................................19 2.4.6 ODP Site 982..............................................................................................19 2.4.7 ODP Site 1050............................................................................................20 2.4.8 ODP Site 1090............................................................................................20 2.4.9 ODP Sites 1258, 1259, 1260......................................................................20 3 METHODS.................................................................................................................23 3.1 Sample Preparation...............................................................................................23 3.1.1 Fossil Fish Teeth Preparation.....................................................................23 3.1.2 Fe-Mn Oxide Coating Preparation.............................................................23 3.2 Sr and Nd Column Chemistry...............................................................................24 3.3 Nd Analysis..........................................................................................................25 3.4 Major Element and REE Analyses from Fe-Mn oxide coatings..........................28

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vii 3.5 Sequential Extraction Procedure...........................................................................29 3.6 Analysis of Nd and Sr isotopes, a nd Rare Earth Elements from Sequential Extractions.............................................................................................................31 3.7 Sr Analysis............................................................................................................32 4 BACKGROUND FOR THE CRETACEOUS STUDY.............................................34 4.1 General Climate Change and Tectonic Orientations............................................34 4.2 Cretaceous Ocean Circulation..............................................................................35 4.3 Ocean Anoxic Events...........................................................................................36 5 RESULTS FROM THE CRETACEOUS OAE STUDY...........................................43 6 DISCUSSION OF CRETACEOUS OAE STUDY....................................................50 7 BACKGROUND ON EXTRACTION EXPERIMENTS..........................................60 8 RESULTS OF THE FE-MN OXIDE COATING EXTRACTION PROCEDURE AND VALIDITY TESTS...........................................................................................62 8.1 Variations on the Ex traction Procedure................................................................62 8.2 Results from Southern Ocean Sites......................................................................65 8.3 Results from North Atlantic Sites.........................................................................69 8.4 Results from Cretaceous Samples........................................................................72 8.5 Tests of Validity...................................................................................................73 8.5.1 REE Plots....................................................................................................74 8.5.2 Strontium Isotopes.....................................................................................78 8.5.3 Major Element Ratios................................................................................80 8.5.4 Sequential Extraction Procedure Results....................................................84 9 DICUSSION OF EXTRACTION RESULTS FROM THE SOUTHERN OCEAN; NORTH ATLANTIC; AND CR ETACEOUS AGE SAMPLES...............................91 9.1 Possible Lithologic Effects on the Extraction Procedure.....................................91 9.2 REE Patterns of Fe-Mn oxide coatings................................................................93 9.3 Sr Isotopes............................................................................................................95 9.4 Major Elements.....................................................................................................97 9.5 Sequential Extraction............................................................................................98 9.6 An Alternate Explanation..................................................................................102 10 CONCLUSIONS......................................................................................................104 LIST OF REFERENCES.................................................................................................108 BIOGRAPHICAL SKETCH...........................................................................................121

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viii LIST OF TABLES Table page 2-1 Nd Isotopic Data for Modern Seawater to Show the Variation in Values of Major Water Masses...................................................................................................7 5-1 Site 1258 mcd and 13C............................................................................................44 5-2 Sr and Nd Values from Cretaceo us Samples from ODP Sites 886, 1050, 1258, 1259, 1260................................................................................................................48 6-1 REE Values from Fossil Fish Teeth Samples Before, During and After OAE2......52 8-1 Nd Isotopic Values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from Southern Ocean ODP Sites 689, 690, and 1090.......................................................68 8-2 Nd Isotopic Values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from North Atlantic DSDP and ODP Sites 608, 647, and 982.........................................72 8-3 Nd Istopes from Fossil Fish Teeth and Fe-Mn Oxide Coatings from Sites 1258 and 1050...................................................................................................................73 8-4 REE Values from Fe-Mn Oxide Coatings................................................................77 8-5 87Sr/86Sr Values from Extracted Material and Foraminifera from Samples from ODP Sites 689, 690, 982, and 1090.........................................................................80 8-6 Major Element Rations from Site 608, 647, 690, 1090, and 1258...........................82 8-7 143/144Nd values for Fossil Fish Teeth, Carbonate, Fe-Mn Oxide Coatings, and Residual Fractions from the Sequential Extraction Samples...................................86 8-8 87Sr/86Sr Values for Seawater, Ca rbonate, Fe-Mn Oxide Coatings, and Residual Fractions from the Sequential Extraction Samples...................................86 8-9 REE Values from Sites 608, 647, 689, 690, and 982 from Three Sediment Fractions...................................................................................................................90 9-2 Percent Nd Contributed to the Bulk Sediment from the Carbonate, Fe-Mn Oxide, and Residual Fraction Separa ted during the Sequential Extraction Procedure..................................................................................................................99

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ix LIST OF FIGURES Figure page 2-1 Variation of the 87Sr/86Sr ratio of seawater through the Cenozoic.............................9 2-2 General Ocean Circulation model............................................................................11 2-3 Nd from sites in the Atlantic sector of the Southern Ocean spanning 20 kyr to present, plotted with 18O values from the GRIP ice core and sea ice variations from the Western North Atlantic. ...........................................................................15 2-4 Modern plate reconstruction.....................................................................................16 2-5 Stratigraphic section of Cretaceous sequence for Site 1258 on Demerara Rise showing the three major lithostr atigraphic intervals recovered:..............................21 3-1 The difference between the Nd(o) values of 11 samples measured on the TIMS and the NU-MC-ICP-MS. ......................................................................................27 4-1 Tectonic plate reconstruction at 90Ma showing the open connection between the Atlantic and Pacific Oceans.....................................................................................40 4-2 The seawater Sr isotope curve with 3 OAEs that coincide with perturbations in the Sr isotopic values................................................................................................41 4-3 Relative ocean crust and pl ateau production over time. .........................................41 4-4 Eustatic sea level curv e of the last 200 Ma. ...........................................................42 5-1 13C and TOC % from ODP Site 1258 from 410-490 mcd. ...................................43 5-2 Nd(t) and 13C values from Site 1258 from 370 to 490 mcd. ................................45 5-3 High resolution 13Corg with the Nd(t) values spanning OAE2 (420-428 mcd) from ODP Site 1258.................................................................................................46 5-4 Nd(t) values from Site 886 in the Pacific Ocean, Sites 1259, 1258, and 1260 from Demerara Rise, and Site 1050 from Blake Nose spanning 65-103 Ma....................47 6-1 87Sr/86Sr seawater curve from 85-100 Ma along with the Sr isotopic values from fossil fish debris collected from Site 1258...............................................................51

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x 5-3 REE plots of modern seawater compar ed to samples from before, during, and after OAE 2. ...........................................................................................................52 8-1 The difference of Nd between fossil fish and Fe-Mn oxide coatings from samples of < 63 m, 63-125 m and >125 m size fractions. S............................63 8-2 Difference of Nd from obtained from fossil fish teeth and samples treated for 4, 2, and 1 hour extraction periods...............................................................................65 8-3 Nd(o) values from fossil fish teeth and Fe-M n oxide coatings from the Southern Ocean Sites...............................................................................................................66 8-4 Nd(o) values from fossil fish teeth and Fe-Mn oxide coatings from DSDP Site 608 and ODP Site 647 from 5.5 to 9 and from 30 to 31 Ma....................................70 8-5 Nd(o) values from fossil fish teeth and Fe -Mn oxide coatings from ODP Site 982 from 9 to 15 Ma........................................................................................................71 8-6 Nd(t) values from fossil fish teeth and Fe-Mn oxide coatings from ODP Sites 1258 and 1090 from 77 to 102 Ma...........................................................................73 8-7 REE plot of four samples from ODP Site 690.........................................................74 8-8 REE plot of the average values from ex tracted coatings from the North Atlantic Sites 608, 647, and 982, the Cretaceous (S ites 1258 and 1050), and the Southern Ocean Sites 1090, 690, and 689...............................................................................76 8-9 Seawater Sr curve over th e past 50 Ma plotted with 87Sr/86Sr values from extracted Fe-Mn oxide coatings...............................................................................79 8-10 Ti/(Fe+Mn) ratios of samp les vs. the difference between Nd values of the fossil fish teeth and the coatings fr om Sites 608, 647, 689, 690 982, 1090, and the Cretaceous samples from Sites 1050 and 1258........................................................82 8-11 Nd(o) and 87Sr/86Sr values from 8 sequential extraction samples............................85 8-12 REE patterns from 8 sequential extractions.............................................................88 8-13 REE patterns for 3 sediment frac tions for sequential extractions. .........................90 9-1 Weight percent opal, carbonate, and te rrigenous material from Site 1090 from 19.2 to 25.1 Ma plotted against the difference between Nd values from fossil fish teeth and Fe-Mn oxide coatings........................................................................92 9.2 Average sedimentation rate versus Nd concentration for Sites 608,647, 982, 689, 690, 1090, and 1258. ..............................................................................................95

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xi Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ND ISOTOPES: INVESTIGATION OF CRETACEOUS OCEAN ANOXIC EVENT 2 AND A SYSTEMATIC STUDY OF FE-MN OXIDE COATINGS By Susanna Whitman Blair August 2006 Chair: Paul Mueller Major Department: Geological Sciences Nd isotopes in seawater are quasi-conservative wa ter mass tracers and, therefore, can be used to reconstruct deep sea circ ulation through time, allowing sci entists to further examine the link between ocean circulation and climate. This two-part study first explores circulation patterns in the North Atlantic during Late Cretaceous Ocean Anoxic Events (OAEs) using fossil fish teeth as an archive for Nd isotopes. Second, iron-manganese (Fe-Mn) oxide coatings on marine sediments are systematically tested as a potential new archive on Cenozoic timescales. A high resolution Nd isotopic record was c onstructed for Site 1258 on Demerara Rise spanning OAE2 and the Mid-Cenomanian Event (M CE). Low resolution Nd isotopic records were also compiled from fossil fish teeth collected from ODP Sites 1259 and 1260 also on Demerara Rise, as well as Site 1050 (Blake Nose), and Site 886 (Central North Pacific). Data indicate that Nd isotopes are unaffected by diagenetic alteration. Average Nd values of 15 before and after the OAEs at Site 1258 suggest that Demerara Rise was highly influenced by weathering off the South American continent. During OAE2 a very large, rapid increase of 8 Nd units coincides with the increase in total organic carbon and the ~6o/oo positive excursion in

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xii 13Corg. Competing causal theories for OAE2 attribute this anoxic event and the major shift in the global carbon budget to enhanced surface productivity or stagnation of the deep ocean. The rapid, positive increase in Nd at Site 1258 approaches values observed at Blake Nose (subtropical North Atlantic) and in the Pacific around this time ( Nd = to ), indicate enhanced, rather than reduced, deep water circulation. This enhan ced circulation may have been associated with increased rates of upwelling, contributing to surface productivity and increased carbon burial. Fossil fish teeth are effective archives for Nd isotopes, yet they are not always present in sediment samples and are laborious to collect. Fe-Mn oxide coatings are present throughout time and space, can be accurately dated, and have pr oven to be reliable archives on Pleistocene time scales. Other studies have not had a method to test the accuracy of the oxide coating values. In this study Nd results from these coatings were compared to fossil fish teeth values for samples as old as the Cretaceous. For ~90% of the samples from the Miocene to Eocene in the Southern Ocean (Sites 689, 690, and 1090) and North A tlantic (Sites 608, 647, and 982), as well as Cretaceous samples from Site 1258 the coatings and fish teeth yielded the same Nd values. A number of independent tests evaluated the sel ectivity and efficiency of the extraction procedure, including Sr isotopic analyses, REE pa tterns, and major element ratios. Sr isotopes were identified as a very conservative test. A se quential extraction procedure was also tested to determine the isotopic signature and REE patte rns of various sediment fractions. It was concluded that terrigenous material in the sedim ents may affect the Sr isotopes, but not the Nd values. Although these results indicate that Fe-Mn oxide coatings are a robust archive of deep sea Nd isotopes, it is necessary to test a few samp les from each site against fossil fish teeh Nd values. Preliminary results indicated that some of the Nd isotopic signal may also be coming from phosphates within the sediment. It can al so be concluded that the rigorous cleaning procedure of fossil fish teeth prior to analysis is not necessary.

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1 CHAPTER 1 INTRODUCTION Throughout earths history a number of c limatic events have been linked to dramatic changes in ocean circulation. Ex amples include the co rrelation between the onset of the Antarctic Circumpolar Current, the thermal isolation of Antarctica, and the development of large ice sheets on Antarcti ca (Kennet, 1977; Scher and Martin, 2006). The correlation between the closure of the Central American Seaway (CAS) and the onset of modern thermohaline circulation, as well as Northern Hemisphere glaciation represents another example. By identifying changes to ocean circulation in the past scientists hope to better understand forcing mechanisms, rates of change, and possible effects of climate change. Global warmi ng is quickly becoming one of the most important issues of our time. The melting of polar ice caps and permafrost, and the intense weather conditions acro ss the globe have many concer ned. By identifying major climatic changes in the past and understa nding their forcing m echanisms we may be better prepared for future climate changes. A conservative tracer for ocean circulation is required to evaluate to the role ocean circulation plays in the development of global climate on geologic timescales. Neodymium is one of the few possible tracers for this property. Neodymium has been used in a number of studies to evaluate cha nges in deep water circ ulation over a range of time scales (e.g. Ling et al ., 1997; ONions et al., 1998; Winter et al., 1997; Frank anNions, 1998; Frank et al., 1999; Vance and Burton, 1999; Frank et al., 2003; Thomas et al., 2003; Martin and Scher, 2004; Piotrowski et al., 2005; Scher and Martin, 2006).

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2 Different water masses can have distinct Nd isotopic values (Piepgras and Wasserburg, 1982 and 1987; Piepgras and Jacobsen, 1988; Bertram and Elderfie ld, 1993; Jeandel, 1993; Shimizu et al., 1994; Jeandel et al., 1998) because the residence time of Nd in the worlds oceans is shorter than the mixing time of the ocean itself (Broecker and Peng, 1982; Elderfield and Greaves, 1982; Piepgras and Wasserburg, 1985; Je andel et al., 1995; Tachikawa et al., 1999) and because the Nd isotopic signature is dominated by the local geology of the source regions. Unlik e other potential tracers, such as 13C or Cd/Ca, Nd isotopes are not fractionated by biological processes or temperature. Tracking deep water Nd isotopes through time and space can lead to greater understanding of past deep ocean circulation patterns. In order to utilize this tool, an effectiv e archive has to be identified that preserves the Nd isotope values over time. Some of the archives that have been used in paleoceanographic studies include ferroma nganese (Fe-Mn) crusts and nodules, fossil fish teeth, and authigenic Fe-Mn oxide co atings (e.g. Albarede and Goldstein, 1992; Frank and ONions, 1998 and 1999; Martin a nd Haley, 2000; Frank et al., 2003; Thomas et al., 2003; Martin and Scher, 2004; Piotro wski et al., 2004; Sche r and Martin, 2006). This thesis presents two unique studies; one applies Nd isotopes from fossil fish teeth to study the relationship between ocean circulation and the development of Ocean Anoxic Events (OAEs) in the Cretaceous, a nd the second evaluates the potential of FeMn oxide coatings on marine sediments as a possible archive for Nd isotopes on Cenozoic timescales. The Cretaceous was a time of drastic cha nges in the worlds oceans. One extreme event during this time was Ocean Anoxic Event 2 (OAE2), which is associated with large scale changes to the oceans carbon budget (e.g. Schlanger and Jenkyns, 1976; Jenkyns,

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3 1980, Arthur et al., 1988; Kuypers et al., 2002). This net bur ial of organic carbon around the Cenomanian-Turonian boundary occurred during the peak of the Cretaceous greenhouse climate interval. Widespread evid ence for this event is present in all the world's oceans in the form of laminated, orga nic-rich silt and claystones virtually devoid of benthic fossils, indicating anoxic bottom wa ters over much of the seafloor. OAE2 is a global event and coincides with shifts in ocean chemistry, extin ction of planktonic nannofossils (e.g. Leckie et al., 2002), the emplacement of the Caribbean large igneous province (LIP) (e.g. Kerr, 1998), and a highsta nd of sea level (e.g. Jenkyns, 1991); yet the ultimate cause of anoxia during this interval is still debated. The de bate centers around whether the anoxic conditions that lead to th e OAE2 were created by: 1) increased decay of organic carbon in response to enhanced surface productivity (largely a surface phenomenon), or 2) reduced ventilation and stagnation (largely a deep water phenomenon). Nd isotopes, which have been shown to eff ectively track ocean circulation, offer a unique opportunity to eval uate whether or not OAE2 was associated with changes in deep ocean circulation. Nd isotopes from fossil fish teeth and debr is were analyzed and compared to carbon isotopic data from OAE2 on the Demarara Rise (ODP Leg 207, Sites 1258, 1259, and 1260) in order to distinguish between propos ed causal mechanisms. Nd isotopic data from Site 886 in the central north Pacific O cean and Site 1050 from the subtropical north Atlantic (Blake Nose, Leg 171B) also helped constrain possible interpretations. Results from this study illustrate that there is a very dramatic response to OAE2 in the Nd isotopic record.

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4 Although fossil fish teeth have proven e ffective for the generation of high resolution Nd isotope records on Cenozoic tim e scales (Martin and Haley, 2000; Martin and Scher, 2003; Thomas et al., 2003; Thomas 2004) and the temporal resolution of Nd records from fossil fish teeth represents an enormous improvement relative to Fe-Mn crusts, the resolution is still not as high as traditional paleoceanogr aphic proxies because the yield of teeth is highly variable. Moreover the method us ed to extract Nd from fossil fish teeth is very labor intens ive. This project explores an alternative archive for creating these records. The dispersed, authigenic Fe-Mn oxide coatings, common on marine sediments, have high concentrations of Nd and have been used to generate high resolution Nd isotope records on glacial-interglacial time s cales (Rutberg et al., 2000; Bayon et al., 2002; Piotrowski et al., 2004). Th is project evaluates the preservation of initial Nd isotopes from Fe-Mn oxide coati ngs over Cenozoic time scales and seeks to identify a simple test of the integrity of the preserved signal.A reductive extraction procedure developed by Rutberg et al. (2000 ) and Bayon et al. (2002) to remove Fe-Mn oxide coatings was modified and applied to selected sediment samples of Miocene to Eocene age from Ocean Drilling Progr am (ODP) Sites 689, 690, and 1090 in the Southern Ocean and from DSDP (Deep Sea Drilling Program) and ODP Sites 608, 647, and 982 in the North Atlantic. To test the validity of the isotopi c values obtained, the coating values have been compared with Nd isotopic values of contemporaneous fossil fish teeth. It is assumed throughout the study th at the value obtained from the fossil fish teeth accurately reflects the Nd isotopic co mposition of the seawat er at the time of deposition (Staudigel et al., 1985; Elderfile d and Pagette, 1986; Martin and Haley, 2000; Martin and Scher, 2004). This method of veri fying the integrity of the signal preserved

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5 in Fe-Mn oxide coatings is unique to this study. The sediment size fraction, extraction time, and extraction agents have been alte red from the original Bayon procedure (Bayon et al., 2002) to obtain Nd isotopic values that match those of the fish teeth. The main concern with this extraction technique is possible contamination from the detrital material, which would undoubtedly alter the isotopic value. Less labor-intensive methods of verifying the integrity of the sign al extracted from the oxide coatings have been tested. These tests were specifically de signed to detect detr ital contamination. The tests include studies of major element ratios, rare earth element (R EE) patterns, and Sr isotopes. During the study a sequential extrac tion procedure was also applied to several samples to determine the Nd isotopic values of several distinct components: the fish teeth, carbonate, Fe-Mn oxide, and residual fr actions of the sediment. The development of a reliable procedure for effectively extr acting Fe-Mn oxide coatings from marine sediments would allow for a more continuous sampling of the ocean sediments and the development of a more complete reconstr uction of ocean circulation through time.

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6 CHAPTER 2 GENERAL BACKGROUND 2.1 Isotope Systematics 2.1.1 Neodymium Neodymium is a lanthanide series element that has seven isotopes. 143Nd is a radiogenic daughter product of 147Sm produced by alpha decay with a half-life of approximately 1.06x10-11 years. The 143Nd/144Nd ratio is measured and commonly reported as Nd. This notation allows small, but signifi cant, variations in the isotopic ratio to be reported in whole numbers relative to a bulk Earth value (DeP aolo and Wasserburg, 1976) and is determine by the equation below. Nd(o) = [(143Nd/144Nd)sample /(143Nd/144Nd)CHUR ] x 104 Where CHUR (Chondritic Uniform Reservoi r) is equivalent to the bulk Earth 143Nd/144Nd ratio or ~0.512638 (DePaolo and Wasse rburg, 1976). Continental material has Nd values of 0 to -50 while mid-ocean ridge basalts (MORB) have values of 0 to + 12 (Piepgras and Wasserburg, 1980). Neodymium is a direct w eathering product from the co ntinents and generally reflects the relative ages and type of the weathered bedrock. The residence time of Nd in the worlds modern oceans is ~1000 years (E lderfield and Greaves, 1982; Piepgras and Wasserburg, 1985; Jeandel et al., 1995; T achikawa et al., 1999 and 2003), which is shorter than the total mixing time of the o cean (~1500 years; Broecker and Peng, 1982). The various ages and types of the weathered material in deep water source regions and

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7 the relatively short mixing time of Nd in the oc eans indicate that Nd isotopes can be used to track deep water masses. Although Nd isotopes in seawater covary w ith other conservative tracers, such as salinity and silica (Rutberg et al., 2000; Goldstein and Hemming, 2003), Nd is not a perfect conservative tracer for water masses b ecause the signal of ocean water masses can be altered by weathering inputs within a ba sin. Frank et al. (2003) termed Nd isotopes quasi-conservative water mass tracers due to this possible modification. One example of this effect is that Pacific waters have an Nd value of ~-4 derived from relatively young Pacific Rim volcanic rocks despite the fact that most of the water masses flowing into the basin have Nd values < -8. However, variations in ocean circulation can still be detected above this weathering signal (P iepgras and Jacobsen, 1988) (t able 2-1). In comparison the North Atlantic, which is surrounded by old Pre-Cambrian cratons, has Nd values of ~-13 to -14. Finally, the Indian Ocean has Nd values of ~-8, which reflects the weathering input from surroundi ng landmasses, as well as a mixture of Atlantic and Pacific values (Piepgra s and Wasserburg, 1979). Table 2-1. Nd isotopic data for modern seawater to show the variati on in values of major water masses Water mass Modern Nd AAIW (Antarctic Intermediate Water) -7 to -8 1 AABW (Antarctic Bottom Water) -9 1 PDW (Pacific Deep Water) -4 2 NAIW (North Atlantic Intermediate Water) -13 3 NADW (North Atlantic Deep Water) -13.5 3 1.Jeandel, 1993; 2. Piepgras and Jacobsen, 1988; 3. Piepgras and Wasserberg, 1987 Neodymium is primarily sourced from con tinental sources including atmospheric dust, volcanic ash, resuspended detrital sediments, dissolved riverine input and river-borne particulates (Goldstein and Jacobsen, 1988; Bertram and Elderfield, 1993; Albarede et

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8 al., 1997; Tachikawa et al., 1999 and 2003). Nd emitted at hydrothermal sources is thought to be scavenged almost immediately and therefore does not have an effect on waters beyond the immediate s ource area (Michard, 1983; Germ an et al., 1990). Nd ions are relatively insoluble and ve ry particle reactive, thus the concentration of Nd in seawater is fairly low, ~4 pg/g in the deep water. Nd is quickly scavenged by detritus, fecal pellets and oxide coatings in the wate r column and deposited on the ocean floor. 2.1.2 Strontium Strontium isotopes have been used in this study as a chronostratigraphic tool as well as an independent te st of the validity of the Nd isotopic value of the extracted Fe-Mn oxide fraction. The Sr isotopic value of the ocean is a func tion of a number of inputs; crustal weathering by riverine sy stems, which have radiogenic 87Sr/86Sr values (~0.7119), mantle derived material from hydrotherma l venting with non-radi ogenic values of ~0.7035 (Palmer and Edmond, 1989), and pore wa ter diffusion which introduces Sr with the isotopic ratio of old marine carbonate s (Hess et al., 1986; Hodell et al., 1990). Strontium has a residence time in the ocean s on the order of several million years (Hodell et al., 1994), which creates a homogeneous ocean with respect to 87Sr/86Sr at any one time in earths history. The major sink fo r Sr is carbonate precipitation, because the Sr2+ ion can easily replace Ca2+. Extensive work has been done to document the changes in Sr over the past 50 Ma (fi gure 2-1). Strontium isotopes il lustrate a general increasing trend throughout the Cenozoic making them a fair ly effective tool for chemostratigraphy.

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9 0.7076 0.7078 0.708 0.7082 0.7084 0.7086 0.7088 0.709 0.7092 0102030405087Sr/86Sr Age (Ma) Figure 2-1. Variation of the 87Sr/86Sr ratio of seawater throug h the Cenozoic. Data from Hodell and Woodruff, 1994; Farrel, 1995; Mead and Hodell, 1995; Martin et al., 1999. 2.1.3 Carbon Carbon isotopes extracted from ocean sedime nts are used to track carbon transfers into and within oceanic reservoirs. Car bon moves through these reservoirs as organic carbon, which consists of both living and dead matter, and inorganic carbon, which is primarily dissolved ions, but can also include atmospheric CO2. Marine foraminifera have preserved inorganic carbon throughout th e geologic record and are commonly used as an archive for car bon isotopes. Carbon isotopes are fractionated during photosynthesis because living organisms preferentially incorporate 12C instead of 13C into their tissue. This fractionation shifts the 13C value of organic matter toward more negative, 12C enriched values, relative to that of inorganic carbon (Goodne y et al., 1980), leaving the oceans enriched in 13C. During times of increased primary productivity in the oceans the

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10 13Corg of foraminifera and bulk organic matter shifts toward more positive values. In this study carbon isotopic ratios in bu lk organic matter are interp reted to represent the global signal of net organic burial and provide an independent record of the position of OAE2. Carbon isotopes can also be used as a tr acer of water mass age. In young deep waters that have recently been at the surface, such as modern North Atlantic Deep Water (NADW), 13C is more positive, reflecting the recent ventilation of surface waters influenced by extensive photosynthesis. As this water circulates and becomes older 12C is progressively returned to the water through organic decay and the 13C becomes more negative. Carbon is consider ed a non-conservative water ma ss tracer because it can be altered by changes in productivity. It provides information about how long the deep water has been away from the surface and the exte nt of surface productivity, but it does not record information about the source region of the deep water. 2.2 General Ocean Circulation The modern ocean circulation model is rela tively well constrained and is controlled by the sinking of cold, saline water in the hi gh latitudes. Highly simplified, the cycle begins as NADW sinks in the North Atlantic, due to its cold temperature and high salinity, both of which make this water relatively dense. This water mass makes its way to the Southern Atlantic where it mixes w ith Antarctic Bottom Water (AABW), which is formed around Antarctica, because of the cold temperatures and high salinities associated with sea ice formation. These water masses co mbine and continue east in a circumpolar current, flow into the Indian Ocean and into th e Pacific, and eventually return through the Drake Passage and the Indonesian Seaway as intermediate and surface waters. This process is referred to as th e global conveyor (Broecker an d Peng, 1982) (Figure 2-2).

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11 Cooling and sinking of warm NADW keeps Eur ope relatively warm for its latitude. The rate of conveyor cyc ling is approximately 103 years (Broecker and Peng, 1982). Figure 2-2General Ocean Ci rculation model, adapted fr om Broecker and Peng, 1982. (www.metoffice.gov.uk) This ocean circulation pattern has evolve d through geologic time. Some of the factors that control the deep ocean circulat ion pattern include openings and closings of oceanic gateways, as well as changes in the thermal gradient and conditions in source regions. The Late Cretaceous circulation, spec ifically, was very different from todays; at that time the North Atlantic had recently opened, creating isolated basins between sills and fractures in the ocean fl oor (Bonatti et al., 1994; Jone s et al., 1995; Handoh et al., 1999). 2.3 Archives of Nd isotopes To determine the Nd value of seawater in the past a physical storehouse or archive has to be identified that incorporates Nd from the seawater into its structure and maintains its integrity through burial and diagenesis. In order to reconstruct Nd changes this archive must be found th roughout space and time, and mu st be datable. Identified

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12 archives include biogenic carbonate, ferromanga nese (Fe-Mn) oxide crusts and nodules, phosphates (particularly fossil fish teeth) and Fe-Mn oxide coatings. Biogenic carbonates have been used as an arch ive for many other chemical proxies (ex. strontium, carbon, and oxygen isotopes); however, the concentration of Nd in carbonates is very low, on the order of a few ppm, because Nd3+ is the wrong size and charge for the carbonate structure (Palmer and Elderfield, 1985). Early studies that attempted to extract Nd from planktonic fora minifera found that 90% of the Nd was in the Fe-Mn coating with only 10% in the carb onate (Palmer and Elderfield, 1985). Nd values obtained from un-cleaned foraminifera yielded 143Nd/144Nd values similar to those of Fe-Mn crusts from a similar location a nd time period (Palmer and Elderfield, 1985). Other studies have suggested that after intensive redox clean ing the Nd isotopic value of planktonic foraminifera records the surface water value (Vance and Burton, 1999). It is, however, unclear if any clean ing can remove all of the coating and produce isotopic values purely from the carbonate (Pomies, 2000). Although foraminifera are abundant throughout the worlds oceans it is unclear wh ether they can be used as effective recorders of either surface or deep -ocean water com positions. Fe-Mn oxide crusts and nodules have proven to be effective archives for Nd ue to high concentrations of Nd, ~ 50 pm (Piepgras and Wasserburg, 1979). There have been a number of successful studies illustrating that these crusts record deep water Nd values through time (e.g. Albarede and Goldstei n, 1992; Burton and Li ng, 1997; Frank and ONions, 1998, Frank et al., 2002). However, there are a few drawbacks to using crusts and nodules. These deposits have exceedingl y slow accumulation rates (on the order of 1-10mm/Myr; Segl et al., 1984; Puteanus and Halbach, 1988) and their sparse

PAGE 25

13 distribution does not always allow for global sampling (A bouchami et al., 1997; Burton et al., 1997 and 1999; Ling et al., 1997; ONions et al., 1998; Frank et al., 1999; von Blanckenburg and ONions, 1999; Frank et al., 2002). The slow growth rate also makes dating this archive very difficult. 10Be/9Be and Co have been used to date these crusts (Frank, 1999); however, this work requires numerous assumptions and Os isotope chemostratigraphy recently highlig hted the errors of some of these ag e models (Klemm et al., 2005). Since the growth rate is exceedi ngly slow the Nd isotopic values of these crusts can record long term trends of ocean water circulation and have provided important end member values for many water ma sses, but they do not record rapid shifts in circulation associated with ma ny climate events. (Table 2-1). Phosphates, especially apatites in the fo rm of conodonts and fossil fish teeth, have proven to be effective archives for d isotopes, (Elderfield and Pagett, 1987; Keto and Jacobsen, 1987 and 1988; Ma rtin and Macdougall, 1995; Martin and Haley, 2000; Thomas et al., 2003; Martin and Scher 2004; Thomas, 2004; Scher and Martin, 2006). The hydroxyfluorapatite structur e of fossil fish teeth cont ains 100-1000 ppm Nd, which is incorporated into the teeth soon after they are deposited on the ocean floor and still in contact with deep ocean water (Wright et al., 1984; Shaw and Wasserburg, 1985; Staudigel et al., 1985; Martin et al., 1995, Martin and Hale y, 2000; Martin and Scher, 2004). Evidence to support this idea include: 1) fish teeth and Fe-Mn crusts from the same water mass preserve the same isot opic value (Martin and Haley, 2000), 2) REE patterns from fossil fish teeth are the same as those for seawater (Elderfield and Pagett, 1986; Reynard et al., 1999), 3) teeth that we re found in variable lithologies and pore fluids, but deposited in the same bottom wate r have the same isotopic value (Martin and

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14 Haley, 2000), 4) the concentration of Nd in teeth does not increase or decrease with depth or age of sediments (Bernat, 1975; Elderfie ld and Pagett 1986; St audigel et al., 1985; Grandjean et al., 1987), and 5) teeth that have been deposited in areas of slow sedimentation and therefore exposed to se awater longer, comm only have higher Nd concentrations (Elderfield and Pagett, 1986; Staudigel et al., 1986; Martin and Scher, 2004). Fossil fish teeth, like Fe-Mn crusts, do eff ectively record the Nd isotopic signal of bottom water; yet, unlike crusts, teeth can be easily dated with the surrounding sediment using paleomagnetism, biostratigraphy, chem ostratigraphy, and orbital tunning. Because of this, relatively high-resolution records ca n and have been produced. Most recently, fossil fish teeth have been used to create a Nd isotopic record of the Southern Ocean in an effort to constrain the timing of the ope ning of the Drake Passage, allowing for a deepwater connection from the Pacific into the Atlantic (Sch er and Martin, 2004 and2006). While fossil fish teeth have been used to produce records with higher resolution than the records produced from Fe -Mn crusts, there are quite a few drawbacks to their use as an Nd archive. The process of picking them from sediments and cleaning them is very time intensive and, more im portantly, fossil fish teeth are not widely distributed temporally and spatially throughout the worlds oceans, leaving large gaps in some records. Another recently explored archive for Nd isotopes is authigenic Fe-Mn oxide coatings (Rutberg et al., 2000 and Bayon et al ., 2002; Piotrowski et al., 2004). Although early work with uncleaned planktonic foraminifera determined that these coatings

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15 recorded ocean water Nd isotopic values (P almer and Elderfield, 1985), this archive has only recently been further investigated. Figure 2-3. Nd from sites in the Atlantic sector of the Southern Ocean spanning 20 kyr to present, plotted with 18O values from the GRIP ice core and sea ice variations from the Western North Atlan tic. Variations in the Nd isotopic record are interpreted to be change s in the strength of NADW and AABW production over interglacial and glacia l timescales. During glacial periods Nd values are more radiogenic due to a gr eater influence of AABW to this site, oxygen isotope values are more negativ e representing cooler climate, and there is more sea ice covering the We stern North Atlantic (adapted from Piotrowski et al., 2004). These coatings occur as a thin veneer of Fe and Mn oxide on the surface of ocean sediments worldwide and throughout time. Wo rk by Hein et al. (1997) has shown the mineralogy of Fe-Mn crust to be both ferruginous vernad ite and Mn-feroxyhyte. This coating is essentially a dispersed accumulation of the same material that is concentrated

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16 in Fe-Mn crusts and nodules. Using Pleistocene and younger sediments from the South Atlantic, it has been shown that these coatings do, in fact, record vari ations in the flow of NADW to the Southern Ocean during interglaci al/glacial cycles (Rutberg et al., 2000 and Bayon et al., 2002; Piotrowski et al., 2004). Piotrowski et al. (2004) demonstrated that Nd isotopic values obtained from Fe-Mn coatin gs even preserve a record of changes in deep water circulation on millennial time scales (Figure 4). It has yet to be determined if this archive can be used for much older sediments. 2.4 Description of Sample Sites Figure 2-4. Modern plate reconstruction from the Ocean Drilling Stratigraphic Nework (www.odsn.de) with DSDP and ODP site locations used in this study. Sites 1259 and 1260 are located in the same area as Site1258. 2.4.1 DSDP Site 608 DSDP Site 608 (42o50.205N, 23o05.252W, 3541.8 m water depth is located on the southern sife of the Kings Trough tect onic complex, which is about 700km northeast of the Azores (figure 2-4). Hole 608 was drilled to a depth of 530.9 m into to upper middle Eocene sediments. Samples used for this study ranged from 119.23 to 208.05 mbsf. The section sampled is primarily wh ite foraminiferal nannofossil ooze, with a

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17 carbonate range of 90-95%. The sedimentation rate for this section is 34 m/m.y. and the age range if from 3.9 to 8.9 Ma. A smear s lide summary from hole 608 core 20 indicates that calcareous nannofossils comprise 78% of the lithology, along with 20% quartz and 2% foraminifers (Ruddiman et al., 1987). 2.4.2 ODP Site 647 ODP site 647 (53o19.876N, 45o15.717W, 3862 m water depth) is located in the southern Labrador Sea off the southern tip of the Gloria Drift and was drilled to further investigate deep ocean circulation between the Arctic and the North Atlantic (figure 2-4). Penetration at Hole 647A was to a depth of 736 m. Sediments used in this study range in ages from 7.3 to 30.6 Ma with corresponding depths ranging from 116.5 to 158.4 mbsf. The samples cover 3 different lithologic uni ts, IIA, IIB, and IIIA. Unit IIA, from 116-119 mbsf is a silty clay underlain by nannofoss il clay. This unit contains a significant proportion of nannofossils and towards the bottom becomes a nannofossil clay with scattered iron/ manganese nodules. The top sect ion (40cm) is composed of 70% clay and 25% quartz silt at the top a nd 70% clay and 25% nannofossils in the bottom section, with minor amounts of mica and pyrite Unit IIB spans from 119 to 135.4 mbsf and consists of two subunits. The upper s ubunit consists is composed of a 65% 75% silty clay with 30% quartz including diatoms and spicules. The lower subunit consists of 90% clay minerals and minor amounts of qu artz silt and mica. There is little to no biogenic carbonate in this section. Th e percent carbonate for both units is le ss than 20% throughout with a sedimentation rate of 46 m/ m.y. Finally Unit I IIA consists of a nannofossil clay and contains both carbonat e and biogenic silica. The biogenic component is 25%-50% and remaining is clay. The average carbonate % for Unit IIIA is 35% with a sedimentation rate of 16 m/m.y. (Shipboard Scientific Party, 1987)

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18 2.4.3 ODP Site 689 ODP site 689 (64o31.009S, 03o05.996E, 2080 m water depth of 2080 m) was drilled during Leg 113 on Maud Rise, which is a topographic high in the Weddell Sea (figure 2-4). The deepest drill depth was 297.3m in hole 689B. The sediment sampled for this project ranged from 60 to 160 mbsf which equates to an age range of 18 to 40 Ma. From 60 to 72 mbsf the main sediment type is very white to white diatom nannofossil ooze. The sediment from 72-160 mbsf is dominated by calcareous nannofossils with radiolaria ns decreasing downwards thro ugh the section. Carbonate percentages throughout the sampled section ra nge from 51.2-98.5% with an average of ~88% CaCO3. Clay is highly variable throughout th e section, with some areas that have little to no clay content and others that ha ve 60-90% smectite. Sedimentation rates range from 7 m/m.y. for 18-23 Ma, 4 m/m.y. fo r 25-33 Ma, and 4.5 m/m.y. for 33-40 Ma (Shipboard Scientific Party, 1988) 2.4.4 ODP site 690 ODP site 690 (65o9.629S, 1o12.296E, 2914 m water depth) was also drilled during Leg 113 to Maud Rise in the Southern Ocean (figure 2-4). The deepest hole was 690B, which recovered 213.4 m. The sediment us ed in this project ranged from a depth of 54 to 114mbsf, with ages of 25 to 45 Ma. Lithology from 54-93 mbsf consists of light grey diatom-bearing nannofossil ooze. Sedime nt from 93-114 mbsf is almost exclusively composed of calcareous biogenic sediment, whic h is primarily white to very pale brown foraminifer-bearing nannofossil ooze. Thr oughout the sampled section there are common (15-30%) to very abundant (60-90%) chlorite, kaolinite, illite, and smectite sections. Carbonate ranges from 50-85% throughout the sa mpled section. The sedimentation rate for 51-93 mbsf is 5.5 m/m.y (Shipboard Sc ientific Party, 1988).

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19 2.4.5 ODP Site 886 ODP Site 886 (44o41.384N, 168o14.400W, 5713 m water dept h) is located on the eastern edge of the Chinook Trough (figure 2-4) For hole C, which was sampled for this study, only recovered 72.4 m sediment, but the olde st sediment is Late Cretaceous in age. Sediment for this project ranged from 64.4 to 70.1 mbsf with ages ranges from 70.1 to 81 Ma (ages were determined using Os isotope s) (Ravizza, personal communication). The lithology of this section is prim arily light to dark brown clay and is described as the classic North Pacific red clay. The cl ay contains 10-30% accessory minerals of authigenetic and/or digenetic origin. Th ere are ferro-manganese crusts and nodules throughout the section (Shipboard Scientific Party, 1993). 2.4.6 ODP Site 982 ODP Site 982 (57o31.002N, 15o51.993W, 1134 m water dept h) is located on the Rockall Plateau, which is about halfway between Iceland and Ireland (figure 2-4). It is a shallow platform at about 1000 m water depth, yet the hole was dri lled in a bathymetric low on the plateau. Drilling reached a dept h of 614.9 mbsf in hole B. Samples were taken from depths of 361.6 to 509.7 mbsf w ith ages ranging from 10.8 to 15.2 Ma. Lithology of this section consists primar ily of nannofossil ooze with very minor variations. There are occasional layers of ash and ooze-chalk, but these were avoided during sampling. Calcareous nannofossils we re the most abundant, while diatoms and radiolarians were very spar se and there were barren inte rvals throughout the section. Calcium carbonate averages about 90% throug hout the sampled interval. Sedimentation rates throughout the section av erage about 35 m/m.y. (Shipboard Scientific Party, 1996).

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20 2.4.7 ODP Site 1050 ODP Site 1050 (30o5.9953N, 76o14.0997W, 2296.5 m water de pth) located on Blake Nose, on the eastern margin of the Blak e Plateau which is due east of Northern Florida (figure 2-3). Samples for this study were taken from 490 to 597 mbsf, which represents ages of 77 to 101 Ma. The samples were taken from Units IV and VI, as defined by the initial reports. Unit 4 extends to 491 mbsf and ranges from a calcareous claystone with nannofossils present to a nannof ossil chalk with clay. Unit 6 extends from 501 to 606 mbsf and is composed of nanno fossil chalk or limesto ne with variable amounts of clay and claystone. The sedimenta tion rate for most of this section is ~10 m/m.y. The carbonate ranges from 30 to 90 weight percent throughout these sequences but is generally higher from 500 to 600 mb sf (Shipboard Scien tific Party, 1998). 2.4.8 ODP Site 1090 OPD site 1090 (42o54.814S, 8o53.998E, 3702 m water depth) is located on the southern flank of the Agulhas Ridge (figure 2-4). The sediments used in this study ranged from 73 to 163 mbsf, with an age range of 16.6 to 12.0 Ma. The lithology is similar throughout the sampled section and cons ists of a mud bearing diatom ooze to a mudand diatombearing nannofossil ooze an d chalk. The carbonate weight percent is highly variable ranging from 080 wt%, but averages to about 30%. Opal averages to ~15% and terrigenous material is ~ 55% throughout the sampled section. The sedimentation rate is about 10 m/m.y. (Shipboard Scientific Party, 1999). 2.4.9 ODP Sites 1258, 1259, 1260 ODP Site 1258 (9o26.000N, 54o43.999W, 3192 m water depth), 1259 (9o17.999N, 54o11.998W 2354 m water depth), and 1260 (9o15.948N, 54o32.633W, 2549 m water depth) are all located on Deme rara Rise, off Suriname, South America

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21 (figure 2-4). Site 1258 is the deepest site on th e western slope of the rise. This site was the most heavily sampled of the three for this project. Samples were collected from 375450 mbsf, representing an age range of 80-96 Ma. The lit hology of the sampled section spans Units III-V, as denoted by the initial reports (Figure 2-5). Unit III (325385 mbsf) is a calcareous nannofossil clay, with an aver age of ~65 weight percent carbonate. Unit IV ranges from 385-445 mbsf and is composed of laminated black shale and limestone. Color variations between these two sediment types record increa sing and decreasing carbonate content, which rang es from 5-95 wt%. Finally Unit V is composed of phosphatic calcareous clay with organic matter. The sedimentation rate across all these lithologies is ~3 m/m.y. (Erbacher et al., 2004). Figure 2-5. Stratigraphic sec tion of Cretaceous sequence for Site 1258 on Demerara Rise (Erbacher et al., 2004) showing the th ree major lithostratigraphic intervals recovered: early Cenomanian and older faulted, synrift siltstones and claystones, Cenomanian-early Campan ian laminated black shales, and Campanian-Paleogene chalk and clayey chalk.

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22 Site 1259 is located on the north facing slope of the rise. Samples were taken from a depth of 441-470.5 with relative ages of 66-70 Ma. The lithology of this section is composed of nannofossil chalk w ith clay and calcareous debris with calcareous siltstone and glauconitic claystone. The carbonate content in this section constitutes ~80 wt% of the sediments and the sedimentation rate is ~4.5 m/m.y. (Erbacher et al., 2004). Finally, site 1260 is on the northwest facing side of the slope. Sampling from this site ranged from 356-386 mbsf representing ages of 70 to 75 Ma. The lithology is nannofossil chalk with foraminifera to calcar eous claystone. The carbonate in this section ranges from 45-80 wt%. The sediment ation rate is 4.3 m/m .y. (Erbacher et al., 2004).

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23 CHAPTER 3 METHODS 3.1 Sample Preparation 3.1.1 Fossil Fish Teeth Preparation Sediment used for all analyses was obtaine d from DSDP or ODP. Fossil fish teeth were handpicked from the >125 m size fraction of 50-60 cc sa mples. The teeth were cleaned following the oxidative/reductive t echnique developed by Boyle (Boyle, 1981; Boyle and Keigwin, 1985). This procedure removes Fe-Mn oxide coatings on the teeth that could alter the isotopic ra tios. Fossil fish t eeth have Nd concentr ations that range from 100 to 1000 ppm and analysis can be pe rformed on samples as small as 8 ng Nd. From each sediment sample 40 g or more of teeth, which is generally 3 or more teeth, were collected and cleaned. The teeth were dissolved in aqua regia to remove any organics remaining after th e cleaning process. After drying down the teeth were redissolved in 30 l of 1.8 N HCl before they we re processed through two cation exchange columns to isolate Sr and Nd. 3.1.2 Fe-Mn Oxide Coating Preparation Upon retrieval from ODP core repositori es, sediment was thoroughly cleaned through 63 m sieves with deionized water. The sediment samples consist of 0.25 to1 g of >63 m size fraction of dry sediment, which wa s placed into a 50 ml centrifuge tube. An initial 20 ml of buffered acetic acid solution was added to each sample and the sample was agitated on an electric shaker until there was no longer a reaction. (ie. the carbonate no loner reacted). The sample was then cen trifuged and the initial 20 ml of acid was

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24 decanted. Then another 10-20 ml of buffere d acetic acid solution was added and this process was repeated until there was no longer a reaction and all the carbonate had been removed. Samples were then sieved using distilled water through 63 m sieves to remove any remaining clay particles that may ha ve been inside any of the carbonate tests. Samples were then centrifuged and the water was decanted. Next, 10-15 ml of 0.02 M Hydroxylamine Hydrochloride (HH) solution was added to each sample to reduce the oxide coatings. Each sample was then agitated for 1.5 hours and centrifuged for 0.5 hours. The supernatant was removed and place d in clean 50 ml centrifuge tubes, which were centrifuged again to remove any residu al particulate matter. The HH solution was then removed and divided into two aliquots one for isotopic analyses and the second for major element and REE analyses. 3.2 Sr and Nd Column Chemistry Fish teeth samples and Fe-Mn oxide samp les were passed th rough 2 columns to effectively separate Sr and Nd from the samples. The first column, or Primary column, used Mitsubishi cation exchange resin with an HCl eluent and isolated Sr as well as the bulk REE. The REE cut was dried down and loaded onto the second column, or the REE column. This column, which separates Nd from other isobars, was packed with Mitsubishi cation exchange re sin and methylactic acid was used as an eluent. Total procedural blanks are ~10 pg of Nd and 100 pg Sr. A seco nd type of REE column was used for the extracted coating samples. This procedure used an HCl elution with quartz columns packed with Teflon beads, which are coated with bis-ethylhexyl phosphoric acid to separate Nd and Sm from the other REE.

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25 Four of the Cretaceous fish teeth and fish debris samples used in this study were spiked and analyzed for Sm to determine the 147Sm/144Nd ratios preserved in the teeth. The range of 147Sm/144Nd values from teeth and fish debris from ODP sites 1050 and 1258 is 0.125, which correlates to corrections of 0.67-0.87 Nd units for this age and agrees well with values repor ted by Scher and Martin (2004) Thomas et al. (2004) and Puceat et al. (2005). The 147Sm/144Nd was also measured on the extracted coating samples and yielded the same correction. Sa mples from these sites were corrected and plotted as Nd(t). For all other samples in this study Nd(o) values were used. For these same spiked samples the concentration of Nd in the fish teeth samples ranged from 200700 ppm, which is well within th e range reported for fish teeth (Martin and Scher, 2004). These concentrations obtained on the TIMS from spiked samples were compared to the Nd concentrations obtained on the Element by REE analysis on the fish teeth and the two techniques produced values that fell we ll within error of one another. 3.3 Nd Analysis The Nd from small (<200 g) fish teeth samples were analyzed on a Micromass Sector 54 Thermal Ionization Mass Spectromete r (TIMS) at the University of Florida (UF). Using dynamic mode Nd was measured as NdO, which increases the efficiency of the analysis. The samples were loaded on zone refined Re filaments using silica gel as a loader. All ratios are normalized to 146NdO/144NdO = 0.722254. Ideally NdO was then analyzed for 200 ratios at .5 V 142NdO, but for very small samples the voltage was set as low as 0.25 V and as few as 100 ratios were c ounted in order to obtain a measurement. Errors for all samples are noted in data tables and graphs. The 143Nd/144Nd value for

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26 repeat analyses of the JNdi-1 standard is 0.512102 0.000014 (2 ). This uncertainty corresponds to 0.27 Nd units. Larger fish teeth samples (>200 g) and extracted coating samples were analyzed on a Nu Plasma Multi-Collector Inductive ly Coupled Plasma Mass Spectrometer (MC-ICP-MS) at the Univ ersity of Florida (UF). 0.5 ml of 2% HCl was added to each dry sample, then 10 l was removed and placed in a sa mpling beaker. An additional 0.99 ml of 2% HCl was added to this aliquot an d the concentration of the sample was then tested on the MC-ICP-MS Ideally 2-5 V of 143Nd was analyzed, and each sample was diluted appropriately after the first test measurement. The instrument and typical operating conditions are describe d in Belshaw et al. (1998). All ratios were normalized to 146Nd/144Nd = 0.7129 to correct for fractionation. Baselines were measured by ESA (electrostatic analyzer) deflection of the beam Under static mode, using the instrument software both wet plasma using a micromist ne bulizer and dry plasma using a desolvating nebulizer (DSN) were used as uptake systems. Only fairly large samples (>70 ppb) can be analyzed with wet plasma. When us ing the DSN a correction factor of 0.000028 or 0.2 Nd unit was applied to samples to make them equate with results using the wet plasma method. Some samples were meas ured using time-resolved analysis (TSA), which produces very precise results with a very small sample size over a much shorter period of time (Kamenov, unpubl ished). This method was developed during the data collection of this project, and, therefore, was only applied for the later analyses. For this method on-peak-zeros were measured for 30 seconds just before sample introduction. Data were acquired in series of 0.2 seconds integrations over an average of a 60 second uptake time.

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27 Both TIMS and MC-ICP-MS methods of Nd isotopic analyses were used for data collection of both fish teet h and Fe-Mn oxide coatings. To compare the results a correction factor was applied to all data collected on the MC-ICP-MS. Over a day of data collection on the MC-ICP-MS the JNdi-1 standard was run 5-10 times and averaged. The difference between this daily averaged value and th e 0.512102 value obtained from the TIMS was used as a correction factor fo r all data collected on that day. The 2 error varied daily, falling between .25 and .6 Nd units. Error bars on data plots reflect the external run error correctly for each m achine and each correction method. Due to variability internal to the MC-ICP-MS it is difficult to develop an overall long-term calibration. To test the correction method used in this study 11 samples were analyzed on both instruments and the corrected results all fell within error of one another (figure 3-1). -0.6 -0.4 -0.2 0 0.2 0.4 0.6 024681012Nd(o) TIMS Nd(o) NUNumber of Samples Figure 3-1. The difference between the Nd(o) values of 11 samples measured on the TIMS and the NU-MC-ICP-MS. The line at 0.0 represents samples that yielded identical values. The fine lines at 0.5 and -0.5 outline the typical error envelope based on TIMS analyses.

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28 3.4 Major Element and REE Analyses from Fe-Mn oxide coatings The portion of the extracted co ating not used for the isotopic analysis was used for major element ratios and REE patterns. Afte r the samples were dried down they were dissolved in 4 ml of 5% HNO3 and left tightly capped on a hot plate overnight. Approximately 200 l of the 4 ml was diluted with ~4 ml of 5% HNO3 (for a final dilution of ~2000 times) for analysis on the Element 2 ICP-MS at UF. Each sample had an uptake time of 1 minute and a wash time of 2 minutes. All REE were analyzed in Medium Resolution mode, while 24Mg, 27Al, 49Ti, 55Mn, and 56Fe. 23Na and 39K were analyzed in High Resolution mode. Four runs and four passes or a total of 16 measurements per isotope were performed. For the major elements the error was 5% and the blank is negligible. USGS whole ro ck standards ENDV, as well as a NOD-A and NOD-P (manganese nodules standards using Axelsson et al., 2002 for the dissolution method) and an in-house standard of AGV were used as correction factors for both majors and REEs. Data were normalized first in the Results Editor by checking and adjusting the calibration curves and second usi ng a drift corrector. The drift corrector, commonly one of the above standards, was run every 5-8 samples and samples were adjusted to compensate for any drift during a given analysis. To do this a correction factor was found between the drifts at either end of sample set and then this correction factor was multiplied by the unknown sample value and the position of that sample in the sequence relative to the other samples. Samp les measured for major elements were also corrected using the NOD-A and NOD-P USGS st andards. Using the counts for each sample reported by the instrument the major element ratios were determined. To correct these ratios the known standard NOD values were divided by the measured NOD values

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29 and all of the unknown sample va lues were multiplied by these counts to concentration conversion. A known standard was not identified for the analysis, all standards and samples were run as unknowns corrected as described. The reported REE for each sample was then normalized to the weight of the starting sediment sample and to PAAS (Post-Archean Australian Shale) (Taylor and McLellen, 1985). The error for REE elements is 5% and the blank is negliable. 3.5 Sequential Extraction Procedure The goal of this procedure wa s to effectively separate the different fractions of marine sediments and obtain REEs and Sr a nd Nd isotopic values and concentrations for each fraction (Bayon et al., 2002). Samples of 0.75 g 0.5 g were weighed out and the weight was recorded, then each sample was placed in a 50 ml pre-weighed centrifuge tube. Using a technique similar to that of the extraction procedure defined above, the carbonate fraction was first removed by adding 40 ml of acetic acid to the centrifuge tube. The weight of this liquid was accura tely recorded for each sample so that concentrations could be calculated. The sa mple was agitated until there was no longer a reaction with the carbonate. The sample was then centrifuged and tw o aliquots of 5 ml each of the acetic acid were removed and set aside. One of these samples was used for REE and major element concentrations an d the other was dried down and used for column chemistry and isotopic analysis. The remaining acid was discarded. Four times (4x) distilled water was adde d to the remaining solid material, the sample was shaken, centrifuged, and the water decanted. This step was repeated twice to remove all of the acetic acid. The sample was then dried in an oven overnight to remove any remaining water and reweighed after it wa s completely dry. The weight difference between the initial and final weights was assumed to represent the weight of the

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30 carbonate. Once dry, approximately 10 g of 1M HH solution was added to each sample. Samples were placed in 75o C water bath for three hours and agitated every 30 minutes (Bayon et al., 2002). This method of extr action was used, as opposed to the one described above for removal of the Fe-Mn oxide coating for Nd analyses, because Bayon et al. (2002) determined that this technique removed the whole of the oxide coating more effectively, leaving the detrital fraction clean for analysis. Once the three hour extraction procedure was complete the sample was cen trifuged and again two 5 ml samples were removed, one for elemental concentrations and the other was dried for isotopic analyses. The remaining solution was discarded and the sample was rinsed twice with 4x distilled water as described above. The sample was again placed in the oven to dry. In a preliminary study hydrogen peroxide was used to remove the organic fr action of each sample. In many cases there was a violent effervescence that caused the loss of some of the sediment. When REE were measured on this fraction the concentra tions were up to three orders of magnitude lower than the values from the other sediment fractions. Also there seemed to be no distinct REE pattern for the organics. Th e organic removal step was subsequently eliminated and the data presented in this study does not include a distinct organic fraction. After the HH step, rinsing, and drying, the remaining sample was removed from the oven and weighed in the pre-weighed centrifuge tube to determine the amount of sediment residue. This residue was then powdered using a mortar and pestle and the sample was split into two portions, one for R EE and one for isotopic analysis. For REE analysis 0.05 g were removed and placed into a beaker containing a drop of 4x water.

PAGE 43

31 One ml of concentrated HF and 2 ml of concentrated HNO3 were then added to each of the REE samples to dissolve the particulates and then the beakers were tightly capped. The samples were heated in an oven at 100 C for 24-48 hours, then uncapped and placed on a hot plate to evaporate. After the samples were dry, 4 g of 5% HNO3 was added to each. The day before analysis the sample s were left on a hotpl ate uncapped to dry overnight, then removed and allowed to cool be fore analysis. For is otopic analysis 0.1 g of sample was removed and placed in a beaker. To this 1-2 drops of HNO3 and 3 ml of HF are added and placed on a hotplate for 2 days. Samples are removed and dried down on a hotplate. Once dry, 2 ml of 6 N HCl is added to the sample to turn it into chloride salts. The sample was left on the hotplate ov ernight, opened and allo wed to dry prior to column chemistry. 3.6 Analysis of Nd and Sr isotopes, a nd Rare Earth Elements from Sequential Extractions For REE patterns samples were analyzed on the ICP-MS using the method described above for major elements and REE. The weight of the acetic acid or HH solution and the dilutions were accounted for in the soft ware when analyzing each sample. The reported values are REE concentrations normalized to PAAS (Taylor and McLellen, 1985). The second aliquots of samples were dried down and used for isotopic analysis. Preliminary tests showed that preparation of the carbonate fraction for column chemistry was fairly difficult. The samples formed a gelatinous mass (probably a calcium chloride substance) that would not fully dissolve in the small amount of 0.75 N HCl used to load samples onto the columns. Once the samples were loaded a carbonate cap commonly formed at the top of the resin inhibiting the fl ow of the eluents. To avoid this problem

PAGE 44

32 the sample was run through the primary columns twice. For the firs t pass the sample was dissolved in 1 ml of 1.7 N HCl and added to the column in 250 l increments. After the sample was loaded 5 ml of 1.7 N HCl is added to remove most of the Ca. This cut was discarded and 4.5 ml of 4.5 N HCl was added to remove the remaining sample including Sr and REEs. This cut was then dried down and run back through primary columns using the normal procedure as explained above. The Sr and REE cuts were both collected. The REE cut was passed through the same columns that were used to elute Nd from the extracted coatings. Analysis of the HH aliquot followed the procedure described above for the other samples treated with HH. The first column el uted Sr and the REEs. Traditional Sr and REE cation columns were used with AG5 0W-X12, 200-400 mesh resin with a 3.5N HCl acid eluent. Both the Sr and REE cuts from the first column were dried down, and the REE cuts were passed through REE columns, to elute Nd, using the procedure defined above for the extracted coatings. Sr isotop es were analyzed us ing the TIMS and Nd isotopes were analyzed using the TRA procedure on the Nu MC-ICP-MS. 3.7 Sr Analysis Sr was isolated by two different methods depending on whether the archive of Sr was fish teeth, Fe-Mn oxide coatings, or forami nifera. The Sr from fish teeth and Fe-Mn oxide coating samples was collected from the primary columns as described above, during the elution to separate Sr and REE. Sr isotopes were also extracted from foraminifera for dating purposes. Fora minifera were handpicked from >125 m size fraction of 50-60 cc samples. The concentra tion of Sr in forams is ~1000 ppm and the smallest sample that can be analyzed is ~50 g Sr. Forams from each sample were

PAGE 45

33 individually broken open and cleaned by sonication with wa ter and methanol. Foraminifera were then dissolved with HCl a nd dried down. Sr was el uted using Sr Spec resin and 4x H2O following the technique of Pin and Bassin (1992). Sr cuts from both types of samples were dried down and analyzed on a Micromass Sector 54 TIMS at UF. Samples were loaded onto Tungsten filaments using Ta2O5 and analyzed for 200 ratios at an intensity of 1.5V 88Sr. Fractionation was corrected to 86Sr/88Sr at 0.1194. The 87Sr/86Sr value for repeat analyses of the NBS-987 standard is 0.712025 0.000023 (2 ). The procedural blank for Sr is ~100 pg.

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34 CHAPTER 4 BACKGROUND FOR THE CRETACEOUS STUDY 4.1 General Climate Change and Tectonic Orientations Extreme climatic, tectonic, and sea leve l changes made the Cretaceous a very dynamic and unique time in earths history, and all may have had a direct effect on ocean circulation. The Cenomanian wa s a relatively cool period, but gradually warmed into the greenhouse conditions of the Cretaceous Ther mal Maximum (CTM) during the Turonian. This was the warmest interval of the last 150 Ma and the peak of the last greenhouse interval (Frakes, 1994). This interval was characterized by: 1) drastic increases in poleward heat transport (e.g. Barron et al ., 1993; Berner, 1994; Barron et al., 1995; Frakes, 1994); and 2) CO2 levels that were four times modern values (Poulsen et al., 1999). Models suggest that poleward heat transport also incr eased from 15-30% to explain the reduced equator to pole gradient during the Turonian (Poulsen et al., 1999). The intense changes in climate, especially the thermal maximum, cannot be directly related to changes in ocean circulation, but there is undoubtedly some correlation in terms of changes in circulation pa tterns and heat tran sport (e.g., Brass, 1982; Arthur, 1987; Calvert and Pederson, 1990; MacLeod and Hube r, 1996; Frank et al., 1999; Erbacher et al., 2001; Wilson and Norris, 2001; Leckie et al ., 2002; Poulsen et al., 2003; Erbacher et al., 2005; MacLeod et al., 2005). Tectonically the Cretaceous was marked primarily by the opening of the North Atlantic Ocean beginning in the Albian. The opening caused large-scale alterations in wind patterns and ocean circulation, and brought about changes to global surface

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35 temperatures. Since circulation was fairly restricted the thermal gradients were low which hindered heat transport. It has b een shown through model simulations that the opening of the North Atlantic, and the gate way between the North and South Atlantic oceans, could have been a factor in the deve lopment of the thermal maximum, as well as reorganization of ocean circul ation and changes to regional climate systems (Poulsen et al., 2003). During the Turonian midlatitude Westerlies devel oped along with a 1-15o warming in the polar regions (Bice and Maro tzke, 2001). Simultaneously, the opening of this seaway reduced the regional equator-to-p ole temperature gradient by as much as 15o C. This caused cooling at the equator, and possible production of warm saline bottom water (Poulsen et al., 1999). 4.2 Cretaceous Ocean Circulation Both changes to plate configuration and changes in global surface temperatures seemed to effect ocean circulation to so me degree, however it is very difficult to constrain this circulation. Using general circulation models there is evidence that the opening of the gateway between the North and South Atlantic in the Late Albian, had a large effect on circulation (e.g. Barron and Peterson, 1989). Prior to this opening there were extremely warm and saline conditions in both the North and South Atlantic Oceans. After the opening there is evidence that Antarctic Bottom Waters fed into the Atlantic, as well as the Pacific and Indian Oceans, drivi ng thermohaline circulation in these basins (Haupt and Seidov, 2001; Poulse n et al., 2001). Contrary to this conclusion, the presence of warm saline bottom waters originating at low latitudes has been identified by comparing 18O values of planktonic a nd benthic foraminifera (e.g., MacLeod and Huber, 1996; Barrera and Savin, 1999).

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36 By the Maastrichtian there is also evidence of intermediate and deep water forming in the high-latitude Southern Ocean and the northern Atlantic which flowed throughout the ocean basins inferred from changes in 13C from benthic foraminifera (e.g., Frank et al., 1999; DHondt and Arthur, 200 2). The limited number of deep sea dri ll sites that penetrated to this age a nd concerns about preservati on of carbon and oxygen isotopes limit what can be determined from these me thods. Modeling simulations produce results that are also contrary to the above conclu sions suggesting that there was no deep water connection between the North and South A tlantic oceans until after the Cenomanian (Handoh et al., 2003). Needless to say, th ere are very few constraints on ocean circulation throughout the Cretaceous. The Mid-Cretaceous opening of the North and South Atlantic Oceans created a complicated ocean bathymetry. There is evidence of secluded basins (e.g. Demarara, Sierra Leone, and Guinea) and large sills that could have interrupted deep sea circulation (Jones et al., 1995). There were also large offset fracture zones a nd transverse ridges, which may have restricted flow (Bona tti et al., 1994; Handoh et al., 1999). 4.3 Ocean Anoxic Events In addition to the large pertur bations in temperature and CO2 and critical plate reconfigurations, the Cretaceous is marked by dramatic perturbations to the global carbon budget recorded as ocean anoxic events (OAE s). Theses events are distinguished by ocean-wide and regional changes from normal pelagic sediments to organic-rich black shales, which were deposited in oxygen defici ent waters. They are recognizable by large increases in total organic car bon content and a large positive 13C excursion in both organic and inorganic carbon (e .g., Arthur et al., 1990; Bral ower et al., 1994). Other

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37 evidence of large-scale changes to ocean chem istry is illustrated by extinctions of some nannoplankton species, which are attributed to these anoxic events (e.g. Wonders et al., 1980; Kuhnt et al., 1986; Jarvis et al., 1988; Erbacher and T hurow, 1997). Six distinct OAEs have been recognized throughout the Late Cretaceous (OAE1a-d, OAE2, and OAE3), two of which can be identified on a global scale, OAE1a and OAE2. These events represent relatively brief periods of time (105-106 years) (e.g. Sageman et al., 2006) and must have been caused by large scal e changes to the ocean environment, yet the ultimate cause is still highly debated. OAE2, or the Bonarelli Even t, which falls at the Cenomanian Turonian boundary about 93.5 Ma falls right at th e height of the Cretaceous greenhouse and re presents the largest perturbation to the globa l carbon cycle in the last 250 Ma. It is characterized by laminated organic-rich silt and claystone w ith no evidence of benthic fossils. Although this event has been studied in numerous globa l localities, the cause of anoxia during this OAE, as well as all the others is still unknown. The prevailing theories simply stated are that the anoxia can be attrib uted to either: 1) a surface dow n phenomenon, such as a sharp increase in surface productivity, or 2) a bottom up phenomenon, denoted by deep water stagnation that could lead to enhanced preservation. The surface down argument states that the warm humid conditions of the Cretaceous led to enhanced physical weathe ring of the continents and an accompanying increased delivery of nutrients to the ocean, resulting in enhanced surface productivity and organic carbon burial (e.g., Pederson and Ca lvert, 1990; Calvert and Pederson, 1992; Erbacher and Thurow, 1997; Wonders, 1980; K uhnt et al., 1986; Jarvis et al., 1988; Weissert 1989). Other mode ls called on enhanced upwelling (Kolonic et al., 2005) or

PAGE 50

38 volcanic production of nutrients in a surface plume (Sinton and Duncan, 1997; Snow et al., 2005), but the premise is the same; excess surface productivity generated an organic rain rate than exceeded the capacity of th e deep ocean to oxidize the material. The opposing mechanism for OAE formati on calls upon enhanced preservation due to changes in deep water properties, notab ly warmer bottom water temperatures, lower oxygen concentrations, and/or sl ower deep circulation leadi ng to stagnation. This model is based on the assumption that high sea le vel and changes to thermohaline circulation caused a decrease in the subs urface oxygen concentration a nd subsequent expansion of the oxygen minimum zone (OMZ) (e.g. Bralower and Thierstein, 1984; Herbin et al., 1986), which resulted in the increased buria l of organic carbon (e.g., de Greciansky, 1984; Arthur, 1990). Changes to circulation could have been caused by warmer surface water temperatures at the poles, which decreased the formation of cold bottom water and increased the amount of warm, high salinity bo ttom waters that formed at lower latitudes (Sinton and Duncan, 1997). Alternatively, oc ean circulation models suggest that deep water continued to form in the high latitudes as the water there was still cooler than at the lower latitudes although it was warmer than modern high latitudes (Bice et al., 2001) Benthic foraminifera 18O values support the idea of warmer bottom water temperatures at this time, ~20oC compared to ~12oC during the late Albian (Huber et al., 2002) and 2oC today. This warm water would c ontain less dissolved oxygen, and might indicate more stagnant deep water circul ation (Savin, 1977; Erbacher, 2001). Sageman and Meyers (2002) illust rated that peaks in 13C values can precede or follow the peaks for total organic carbon (TOC) for OAE2. This suggests the anoxia does not simply result from oxygen depletion due to high organic carbon rain rate s. Herrle et al. (2003)

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39 examined the forcing mechanism of bl ack shale formation during OAE1 and found variations between oxygen isotopes, and calcareous nannoplankton, palynomorph, and benthic foraminifera assemblages that reflec t changes to climatic conditions. The study concluded that these variations were cause d by feedback mechanisms within a monsoonal climate system, which involve warm/humid an d cool/dry cycles. They argue that the black shale formation and deep water anox ia occurred during humid conditions when high precipitation and low evaporation resulte d in decreased deep water formation and stagnation. Another popular theory for the cause of anoxia focuses on changes in ocean and atmospheric chemistry caused by the eruption of large igneous provinces (LIPS), namely the Caribbean province and/or an increase in hydrothermal activity associated with increased ocean crust production, both of which coincide with OAE2 (Arthur et al., 1997; Weissert, 1989; Larson, 1991; Sinton and Duncan, 1997; Ke rr, 1998; Jones et al., 2001; Brumsack, 2005; Snow et al., 2005). Weissert (1989) argues that increased subsurface volcanism put excess CO2 into the atmosphere, which in turn accelerated continental weathering increasing the supply of nutrients to th e oceans. Another argument suggests that the subsea eruption was so large th at the buoyant hydrothermal plume brought limiting nutrients in the form of dissolved meta ls to the surface of the ocean, resulting in drastically increased surface productivity (Sin ton and Duncan, 1997; Snow et al., 2005). These LIPS eruptions are believed to have be en 3 orders of magnitude larger than the largest mid-ocean ridge event (Sinton and Duncan, 1997) and the increase in O2 consumption by the oxidation of sulfides a nd metals could have overwhelmed the poorly oxygenated water below the mixed layer leading to brief periods of seawater anoxia and

PAGE 52

40 the extinction of some bottom dwelling organisms. Plate reconstructions for this time highlight an open gateway in the current Ca ribbean region, connecti ng the Atlantic and Pacific (Lawver et al., 1994; figure 4-1). Th is configuration would have assured that events in the Pacific influenced at least th e northern Atlantic (Sin ton and Duncan, 1997). Figure 4-1. Tectonic plate rec onstruction at 90Ma showing the open connection between the Atlantic and Pacific Oceans (Lawver et al., 1994) Interestingly, a number of the OAEs thr oughout the Mesozoic coincide with large perturbations to the Sr isotopic curve (figur e 4-2). The OAEs that occurred during the Jurassic, the Early Aptian, and the Cenoman ian-Turonian (OAE2) all have sharp nonradiogenic excursions in the 87Sr/88Sr value (Jones and Je nkyns, 2001). The most probable cause for these excurs ions is the increase in hydr othermal activity associated with the eruption of LIPS a nd crust production (figure 4-3) Given that OAE events punctuate a long interval of increased crustal producti on, Jones and Jenkyns (2001) suggest that the increased nutrients and CO2 from these out-gassing events simply preconditioned the oceans for anoxia, but ther e had to be another simultaneous variable, such as sea level change, that pushed the ocean into complete anoxia.

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41 Figure 4-2. The seawater Sr is otope curve with 3 OAEs that coincide with perturbations in the Sr isotopic values (from Jones and Jenkyns, 2001). Figure 4-3. Relative ocean crust and plateau production over time. The line represents the position of OAE2 (adapted from Jones and Jenkyns, 2001). Production rates from 120 to 80 Ma are higher than the preceding or subsequent intervals. A dramatic sea level rise (Figure 4-4) also coincides w ith OAE2 and OAE3 and increased ocean crust production (Haq et al., 1988; Jenkyns, 1991). Erbacher and Thurow (1997) proposed that this increase in s ea level drowned carbonate platforms,

PAGE 54

42 thereby leaching nutrients into the oceans, wh ich in turn caused an increase in primary productivity. Given that OAEs are isolated, relatively shor t events, Jones and Jenkyns (2001) proposed that global warming associ ated with hydrothermal activity and crust production may have preconditioned the ocean, while sea level rise provided the final trigger for the event. Figure 4-4. Eustatic sea level curve of the last 200 Ma. The line represents the position of OAE2 and correlates fairly well to a sea level high stand (adapted from Jones and Jenkyns, 2001). Among the many theories for enhanced anoxia during the Late Cretaceous, the most popular theories rely on 1) increased pr oductivity or 2) increased preservation as a function of a change in circul ation, and it has been difficu lt to distinguish between the two. Nd isotopes have been shown to eff ectively record changes in ocean circulation independent of changes in productivity. By obtaining a record of Nd values over an anoxic interval, it may be possible to test wh ether changes in deep ocean circulation were related to periods of anoxia. If there is no change in Nd va lues it could be imply that OAEs were caused chiefly by an increase in su rface production.

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43 CHAPTER 5 RESULTS FROM THE CRETACEOUS OAE STUDY The 13Corg values measured at site 1258 on Deme rara Rise (figure 2-4) record the large positive excursion typical of OAE s during both OAE2 and the Mid-Cenomanian event (figure 5-1; table 5-1). This work will primarily focus on the OAE2, which spans from 422.26 to 423.81 mcd, but the Mid-Ceno manian Event (MCE), another anoxic event, is also clearly distinguishable at 448.18 mcd. Both events record excursions of ~6 (MacLeod, unpublished data), which is the sa me shift documented by Erbacher et al. (2006). The total organic carbon (TOC) jump s from ~13% to nearly 30% during OAE2 (figure 5-1). -30 -28 -26 -24 -22 -20 5 10 15 20 25 30 410420430440450460470480490 13Corg TOC%13C (VPDB)TOC%mcd Figure 5-1. 13C and TOC % from ODP Site 1258 from 410-490 mcd. The green box from 422-424 mcd represents OAE2 and the aqua box is the MCE spanning from 448 to 453 mcd.

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44 Table 5-1. Site 1258 mcd and 13C mcd 13C vs VPDB 414.78-27.09 414.83-26.92 415.11-24.33 416.77-27.19 418.24-27.20 420.29-27.10 421.51-27.36 421.81-27.12 422.09-26.31 422.26-21.99 422.62-23.51 422.96-22.32 423.22-22.53 423.81-22.25 425.71-27.22 426.44-28.48 427.32-28.50 427.48-28.09 428.30-28.12 428.36-28.27 429.60-28.24 445.43-28.75 448.18-21.89 450.22-27.39 452.53-28.97 456.04-28.36 462.68-28.92 467.33-28.68 481.87-29.02 Unpublished data from McLeod. OAE2MCE To determine whether there was a change in ocean circulation associated with OAE2 and the MCE in the North Atlantic Nd(t) was measured for Site 1258 over the interval encompassing both carbon isotope sh ift. Neodymium isotopes were sampled from 375 to 480 mcd at fairly low resolu tion, averaging about every 30 kyr. The Nd(t) values prior to MCE and between the MCE an d OAE2 were fairly nonradiogenic with values as low as -16 and as high as -13 Nd units (figure 5-2; table 5-2). The largest anomaly prior to OAE2 is the large peak that coincides with the MCE at 448.18 mcd

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45 where the Nd(t) value spikes to -10.6. After OAE2 Nd(t) values drop back to nonradiogenic values of -13.5 to -17.8. -18 -16 -14 -12 -10 -8Nd (t) -30 -28 -26 -24 -22 -20 38040042044046048013Cmcd Figure 5-2. Nd(t) and 13C values from Site 1258 from 370 to 490 mcd. The green box represents OAE2 and the aqua box represents the MCE. During OAE2 Nd(t) values increase dramatically by nearly 8 Nd units peaking at 8.2. This transition occurred fairly rapidly an d is tightly correlate d to high resolution 13Corg results for the same core (Erbacher et al .,2005) (figure 5-3). The rate of increase at the start of the event is very similar betw een the two proxies and the peak of each falls within 130 cm; Nd peaks at the onset of the event at 425.29 mcd and 13Corg peaks at 425.16 mcd. Based on 13Corg Erbacher (2005) defines th e anoxic interval between 422

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46 to 426 mcd. The Nd excursion falls almost precisely within these limits (421.8 to 426 mcd) and the small discrepancy that exists may be a function of sampling frequency. -18 -16 -14 -12 -10 -8 -6 -30 -28 -26 -24 -22 -20 -18 420421422423424425426427428 Nd t 13CorgNd (t)13Corgmcd Figure 5-3. High resolution 13Corg from Erbacher et al., 2005 with the Nd(t) values spanning OAE2 (420-428 mcd) from ODP Site 1258. To determine the distribution of Nd isot opes during the Mid-Cret aceous fish tooth or fish debris samples were also analyzed from Site 886 in the Pacific Ocean and Site 1050 at Blake Nose (figure 2-4). Low resolution sampling from these sites illustrates that values from 70 to 81 Ma at Site 886 were more radiogenic than any other site sampled in this study, ranging from -4 to -5.5 (figure 5-4; table 5-2). Samples from 95 to 102 Ma at Blake Nose (Site 1050) also yielded relatively radiogenic Nd(t) values of -5, but ranged down to .5 at 77 Ma. Sites 1259 and 1260 with pr esent water depths of 2354 mbsl and 2549 mbsl respectively represent shallower locations than Site 1258 (present water depth of 3192

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47 mbsl). Samples were analyzed from these sites to determine whether the very negative Nd values observed at Site 1258 were uniqu e. From ~66 to 71 Ma Site 1259 yielded values that ranged from -15 to -16.5 Nd units. Site 1260 samp les yielded relatively consistent values around -16 from 70 to 75 Ma. At 70 Ma data points from 1260 and 1259 are within error of one another at a value of -15.85 Nd units. -18 -16 -14 -12 -10 -8 -6 -4 -2 65707580859095100 886 1259 1260 1258 1050 Soudry 2004 Puceat 2005Nd (T)Ma Figure 5-4. Nd(t) values from Site 886 in the Pacific Ocean, Sites 1259, 1258, and 1260 from Demerara Rise, and Site 1050 fr om Blake Nose spanning 65-103 Ma. The green box represents OAE2 and the aqua box shows the position of the MCE. Additional data includes Nd values from the Negev in Israel (Soudry et al., 2004) and Tethyan values from France (Pucat et al., 2005).

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48 Table 5-2. Sr and Nd values from Cr etaceous Samples from ODP Sites 886, 1050, 1258, 1259, 1260 Sample namemcd A ge (Ma) 1 8 7Sr /86 Sr 2 143/144 Nd 3 Nd ( o ) 4Nd ( t ) 5147Sm/144NdPacific 886-C 8-1 6064.4070.10.707952.3E-05 886C 8-1 112.564.9071.50.512389-4.86-4.190.25 886-C 8-2 122.566.5071.50.707962.3E-050.512356-5.51-4.840.25 886C 8-3 122.568.0075.80.512392-4.80-4.130.25 886C 8-4 122.569.5077.80.512415-4.35-3.680.25 886-C 8-5 11370.93800.708122.3E-050.512395-4.75-4.080.25 886C 8-6 5271.82810.512382-4.99-4.320.25 Atlantic/Blake Nose 1050 20-1 33490.6377.000.512179-8.95-8.440.25 1050 27-2 103558.2598.300.512349-5.64-4.770.25 1050 29-2 102577.4599.730.512334-5.93-5.060.25 1050 31-2 103596.65101.300.512337-5.87-5.000.25 Atlantic/DemeraraRise 1258A 38-1 105A375.2080.000.511804-16.27-15.440.25 1258A 42R -1 8414.8392.620.707582.3E-050.511824-15.88-15.010.25 1258A 42R-1 65415.4092.670.707532.3E-050.511872-14.95-14.080.25 1258A 42R-3 60418.2492.900.511899-14.42-13.550.600.1250 1258B 45R-1 95419.2893.040.707552.3E-050.511724-17.83-16.960.75 1258B 45R-1 95419.2893.040.511748-17.36-16.490.43 1258B 45R-1 96419.2993.050.511849-15.39-14.520.32 1258B 45R-3 36420.5493.100.511864-15.10-14.230.32 1258B 45R-3 51420.6993.180.707592.3E-050.511783-16.67-15.800.25 1258A 42R-5 12421.2993.210.511841-15.55-14.680.60 1258A 42-6 2421.5193.240.511945-13.52-12.650.60 1258A 42-6 32421.8193.280.511846-15.45-14.580.600.1256 1258A 42-6 60 422.0993.290.511940-13.62-12.750.60 1258A 42R-6 65422.1493.320.707572.3E-050.512028-11.90-11.030.25 1258A 42R-6 95422.4493.350.707572.3E-050.511938-13.66-12.790.25 1258A 42R-6 115422.6493.370.707592.3E-050.511921-13.99-13.120.25 1258A 42R-7 7422.9693.400.511967-13.09-12.220.60 1258A 42R-7 25423.1493.420.707602.3E-050.511978-12.87-12.000.25 1258A 42R-7 70423.5993.460.707602.3E-050.512175-9.03-8.160.25 1258A 42R-7 92423.8193.480.707742.3E-050.512074-11.01-10.140.25 1258C 17X-1 85425.2993.520.512145-9.62-8.750.60 1258C 17X-1 105425.4993.530.512120-10.10-9.230.28 1258C 17X-1 125425.6993.550.511841-15.55-14.680.28 1258C 17X-2 10425.9393.570.511847-15.43-14.560.32 1258C 17X-2 30426.1393.600.511805-16.25-15.380.60 1258C 17X-2 70426.5393.700.511766-17.01-16.140.60 1258B 47R-1 23430.4093.900.511917-14.06-13.190.32 1258B 48R-1 111436.4594.500.511764-17.05-16.180.32 1258B 49R-1 44439.2094.970.707602.3E-050.511822-15.92-15.050.25 1258B 49R-3 30441.7395.210.511853-15.32-14.450.25 1258A 45R-2 57445.4395.400.511822-15.92-15.050.600.1262 1258A 46R-1 0448.1895.500.512049-11.49-10.620.32 1258A 46R-2 68450.2295.600.511859-15.20-14.330.600.1218 1258A 46R-4 33452.5396.000.511812-16.11-15.240.60 1258A 47R-1 12456.0496.590.707642.3E-050.511873-14.93-14.060.50 Table 5-2. Continued ___________________________________________________

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49 1258C 27R-2 0480.2998.930.707552.3E-050.511935-13.71-12.840.25 1258C 32R-CC 505.95101.000.707592.3E-05 1259 1259B 13R-1 114441.9166.000.511837-15.63-14.960.32 1259B 13R-7 40442.6067.000.511833-15.70-15.030.32 1259B 14R-2 90452.0668.000.511758-17.17-16.500.32 1259B 15R-1 76458.9069.000.511800-16.35-15.680.32 1259B 15R-3 58459.0370.000.511794-16.46-15.790.32 1259B 15R-6 70459.6471.000.511844-15.49-14.820.32 1259B 16R-1 56470.9872.000.511836-15.64-14.970.32 1260 1260A 39R-1 78357.1270.100.707722.3E-050.511788-16.58-15.910.25 1260A 40R-1 109369.0572.300.707702.3E-050.511776-16.81-16.140.25 1260A 40R-3 104372.0072.900.707712.3E-050.511801-16.33-15.660.25 1260A 42R-2 77389.8975.000.707662.3E-050.511783-16.68-16.010.251. Ages for Site 886 from Ravizza, unpublished data.; for Site 1050 from Shipboard Scientific Party, 1998; and for Sites 1258, 1259, 1260 from Erbacher, 2004.2. Measured 87Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (2 ) and normalized to86Sr/88Sr = .11943. 143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and are then normalized to Jndi-1 = 0.512103 (TIMS average)Nd(o) = [( 1 4 3 Nd/ 1 44Nd)sample/( 1 4 3 Nd/ 1 44Nd)CHUR-1] x 104 Nd(t) = [( 1 4 3 Nd/ 1 44Nd)sample(t)/( 1 4 3 Nd/ 1 44Nd)CHUR(t)-1] x 104 using 1 47Sm/ 1 44Nd

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50 CHAPTER 6 DISCUSSION OF CRETACEOUS OAE STUDY The Nd values for the Cretaceous study were de rived from fossil fish teeth and fish debris. An important consideration for mate rial of this age is whether these values represent contemporaneous bottom waters, as they do for younger samples (e.g. Staudigel et al., 1985; Martin and Scher, 2004), or if the values have been influenced by diagenetic alteration. There are several lin es of evidence to suggest that the shift seen in the Nd values at Site 1258 does, in fact, represent a change in ocean water mass. Firstly, the lithology across the OAE2 and the MCE intervals is consistent. For 15 Ma throughout the Cenomanian and Turonian thinly lamina ted, organicrich black shales were deposited, with no change in lithology. Th e primary lithologic boundary occurs instead in the Late Campanian; however, background va lues are the same before and after this change. Thus, there is no lithologic change a ssociated with the large shift in Nd isotopes, and no Nd isotopic change associat ed with the lithologic boundary. Secondly, the large positive excursion in the Nd isotopes could be created by diagenetic alteration from young vo lcanic material. To test th is theory Sr isotopes were analyzed from the fish teeth and debris, wi th the expectation that alteration in the presence of volcanic ash would pr oduce a correspondin g shift in the 87Sr/86Sr value toward less radiogenic values. Strontium isotope s measured in fossil fish teeth from Site 1258 are much more radiogenic than the 87Sr/86Sr seawater curve. Figure 6-1 illustrates that the Sr isotopes preserved in the fish debris are shifted toward continental values rather than young volcanics.

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51 Figure 6-1. 87Sr/86Sr seawater curve from 85-100 Ma (Jones and Jenkyns, 2001) along with the Sr isotopic values from foss il fish debris collected from Site 1258. REE patterns measured on fish teeth and debris provide further support for the lack of diagenetic alteration. REE were m easured from samples before, during, and after OAE2 to determine if there was any change ac ross this interval. If the anomaly were caused by diagenesis (suggesting that the excursion during th e event was the product of young volcanic input), the REE patterns from be fore and after the excursion might be expected to be different from the pattern duri ng the event. In particular, samples affected by diagenesis in the sedimentary environment would be expected to have flatter REE patterns typical of shale or terrestrial inputs, when normalized to PAAS. However, all of the samples have MREE enrichment relative to shale, suggestive of REE fractionation into apatite (figure 6-3) (e.g. Reynard et al ., 1998) and do not seem to be influenced by volcanics, which would be recorded as an en riched HREE pattern. All the samples also have a similar Ce anomaly indicating that they were deposited under similar redox conditions (Grandjean et al ., 1987; Lecuyer et al., 2004). 0.7073 0.7074 0.7075 0.7076 0.7077 0.7078 859095100 sea water fish teeth87Sr/86SrMa OAE2 MCE A lteration toward volcanic Alteration toward continental material

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52 0.01 0.1 1 10 100 1000Normalized sample/ PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu Figure 5-3. REE plots of modern seawater (De Baar, 1985) compared to samples from before, during, and after OAE 2. All pr ofiles are normalized to PAAS shale (Taylor and McLellen, 1985) REE pattern for modern seawater from 3000 m (De Baar et al., 1985). Table 6-1. REE values from Fossil Fish Teet h Samples from Before, During and After OAE2 SampleLaCePrNdSmEuGdTbHoYbLu Before31.62725.02138.07243.61046.46753.72170.37748.38636.92321.38119.013 Before19.78314.62119.92922.74324.57926.79330.57823.43620.39916.05815.377 Before21.76311.01716.47818.86418.52322.85725.40020.85821.67017.76917.697 During67.77647.38768.52580.87185.371103.068115.32797.00092.68566.88561.319 During57.74344.31867.01979.92298.529134.449131.601120.295111.47969.61157.463 After126.32915.99820.56522.11622.19026.31032.65225.81431.09233.68931.451 After15.30410.72515.45317.59018.63821.38623.66020.45620.84917.74117.354 After10.4778.66711.60713.31614.46317.07619.47915.60914.35411.51710.835 Notes: 1Sample values multiplied by 10 Error is 5% Finally, diagenetic alteration of the Nd isotopes might be expected to coincide with lithologic boundaries. The Late Cretaceous section measured for this study has a very consistent lithology of black shale, which c ontinues from 92.6 to 98.5 Ma and crosses the Cenomanian-Turonian boundary and OAE2. The largest change in lithology in the interval of interest occurs at 415 mcd at the hiatus/condense d interval that separates the

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53 black shale from chalk (figure 2-3). Th ere are undoubtedly changes in diagenetic conditions across this boundary, yet the Nd values are unaffected (figure 4-2) The Nd(t) values reported at Demerara Rise, from Sites 1258, 1259, and 1260, before and after OAE are extremely nonradioge nic (-14 to -17). Th ese values are lower than any other values reported over this time period, suggesti ng that there was a separate and distinct water mass bath ing this site. Published Nd values for the Late Cretaceous include values of 2.5 to -5.5 for the central Pacific (Thomas, 2004; Frank et al., 2005) and values of -7 to -12 for the Tethys (Sti lle and Fisher, 1990; Soudry et al., 2004; Pucat et al., 2005). Values from Pucat (2005) and Soudry (2004) are plotted on figure 5-4 and represent a distinct water mass from the one bathing Demerara Rise before and after the anoxic events. However during the events the excursions at Site 1258 are similar to, although slightly less radiogenic than, thes e Tethyan water masses. The background values reported in this study ar e also lower than the modern North Atlantic, which has the most nonradiogenic value for a major modern water mass, with values of about -13 (e.g. Piepgras and Wasserberg, 1987; Lacan and Je andel, 2005), and lower than any other reported Nd value for a major water mass in the Cenozoic (Burton et al., 1997; Ling et al., 1997; ONions et al., 1998; Burton et al., 1999; Frank, 2002; T homas et al., 2003; Scher and Martin, 2004; Soudry et al., 2004; Thomas, 2004; van der Flierdt et al., 2004; Frank et al., 2005; Sche r and Martin, 2006). During the Late Cretaceous the North Atla ntic was a young ocean with large sills and ridges that could have restricted deep ci rculation (Bonatti et al ., 1994; Jones et al., 1995; Handoh et al., 1999). In particular, there is evidence that there was no deep connection between the North and South Atlan tic at this time (Kennett, 1982; Frank and

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54 Arthur, 1999). The nonradiogenic values from Demerara suggest that this may have been a relatively isolated basin that was aff ected by proximal weathering from the South American continent. Local weathering of th e Trans-Amazonian Proterozoic Shield or the Archean Guiana Highland would have intr oduced nonradiogenic Nd into the bottom waters in this region (White and Dupr, 1985) This idea of an isolated basin around Demerara is further supported by the Nd values at Blake Nose that are much more radiogenic over this period, suggesting they may have been influenced by the open flow between the North Atlantic and the Pacific (figure 5-4). The most intriguing aspects of the Nd data from Demerara Rise are the large Nd positive excursion of 8 units and the close, if not exact, correlation to the 13Corg excursion during OAE2, as well as the MCE. OAE2 spans about 4 m of sediment at Site 1258 and is believed to represent 563-601 k.y. based on an orbitally tuned record (Sageman et al., 2005). Given that the Nd excursion is not the result of diagenetic processes, the most likely cause is a change in deep water circulation at this site during the anoxic event. This conclusion argues against the theory that OAE2 is caused by an increase in primary production (e.g., Peders on and Calvert, 1990; Calvert and Pederson, 1992; Erbacher and Thurow, 1997 Wonde rs, 1980, Kuhnt 1986, and Jarvis, 1988, Weissert 1989), as productivity alone would not alter the Nd value. In addition, the Nd isotopic evidence that Demerara Rise is locat ed in an isolated basin before and after OAE2 argues that OAE2 is not the product of increase in preserva tion caused by deep water stagnation (Savin, 1977; Er bacher, 2001). Instead the Nd changes at this site indicate a rapid onset of mixing or changes to flow patterns concurre nt with changes to the carbon isotopes. Any theory for the form ation of OAE2 must take into account the

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55 shift to radiogenic Nd values over the event and the correlation to the positive shift in 13C values, which implies an increase in produc tivity and/or preservation. There are few hypotheses presented in the lite rature that would explain bo th of these proxies. One possible explanation of th e data is that the sea level transgression across the CenomanianTuronian boundary (Jones and Jenkyns, 2001) may have led to a connection between deep waters at Demerara Rise and Blake Nose. Mixing between the Blake Nose endmember (-5) and the Demerara endmember (-16) could produce the observed excursion value of up to Nd. In terms of 13C, the sea level rise would have drowned continental shelves thereby releasi ng nutrients into the ocean and leading to increased productivity, which in turn caused the anoxia (Haq et al ., 1988; Jenkyns, 1980; Jenkyns, 1991). Thus, a rise in sea level coul d explain both the enhanced deep water circulation and increased surface productivit y. Jenkyns (1980) found evidence of rapid sea level rise in both the Western Interior Seaway (WIS) and in Northern Europe associated with both OAE2 and OAE3. The tr ansgressive events appeared to have relatively short durations similar to those of the OAEs; however, the ages were poorly constrained. Although the highstands in th e WIS and Northern Europe seem to peak during OAE2, the global sea level record peaks at the end of the event (Jenkyns, 1980). An additional problem with this theory is that every sea level rise is not associated with an OAE and some of the OAEs (e.g. OAE1c) are not associated with a sea level transgression (Jones and Jenkyns, 2001). In this scenario, the ocean at the time of the Cretaceous OAEs must have been preconditione d by some other mechanism so that sea level rise could have such a dramatic effect.

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56 Another proposed mechanism for OAEs is the drastic increase in ocean crust production or Caribbean LIP formation (Sinton and Dun can, 1997; Jenkyns and Jones, 2001; Leckie et al., 2002; S now et al., 2005). This erup tion would have: 1) increased CO2, which in turn would lead to an incr ease in primary production and continental weathering, and 2) increased nutrients associat ed with hydrothermal venting or enhanced continental weathering, there by leading to increased produc tion (Vogt, 1989; Erba, 1994; Kerr, 1998; Jones et al., 2001; L eckie et al., 2002; Snow et al., 2005). This increase in productivity would account for the increased 13Corg values and the increased organic rain would lead to anoxia. In terms of Nd, the Nd value of oceanic basa lt is ~+10, thus the shift in Nd isotopes observed at Demerara Rise could reflect the input from basalt weathering or hydothermal input s. There are two assumpti ons associated with this theory. Firstly, there would have to be an open gateway for mixing between the deep or intermediate water directly affected by the eruption and the water at Demerara Rise. Elemental abundances measured by Orth in the WIS, the Atlantic, and Pacific show large peaks during OAE2 that are indicative of incr eased seafloor spreading and hydrothermal processes. These anomalies are larger in the west and get smaller toward the east traveling from the Pacific into the Atlantic (1993). This west to east trend possibly indicates a west to east circulation pattern, thus connecting the erup tion site (equatorial eastern Pacific) with Demerara Rise. The second assumption is that the anoxic conditions would have prevente d the quantitative rem oval of Nd from hydrothermal vents sites. In modern oceans Nd is effectively removed at hydrothermal vent sites by Fe-Mn hydroxides (Michard et al., 1983; German et al., 1990), and is not circulated into the

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57 ocean; however, the situation may have been very different under anoxic deep water conditions. The problem with the LIP and increased sea floor production hypothesis is that it has been established that the basin surrounding Demerara rise was effectively isolated from other deep water masses (e.g. the one at Blake Nose), thus the eruption had to have a major effect on the surface water in order for it to affect deep to intermediate waters at Demerara. Otherwise some other process w ould have had to be coincident with the eruption of the LIPS and increase in ocean cr ust production, such as sea level rise or a change in upwelling. A greater problem is that there were two pul ses of volcanism from the Caribbean LIP, as recorded in the WIS (S now et al., 2005). Due to limited correlation between the WIS and Demerara Rise it is difficult to determine whether the two peaks seen in the Nd record, at 423.5 and 425.5 mcd, could be an effect of the two volcanic pulses. The pulses of volcanic activity identified by Erbacher (2004) do not correlate to peaks in the Nd record. There is also no evid ence for a volcanic event associated with the mid-Cenomanian event for which there are similar shifts in 13C and Nd. The final hypothesis that could explain the positive excursions in both the 13C and the Nd values across OAE2 is a change in th e upwelling pattern at Demerara Rise. Upwelling would effectively brin g nutrient rich waters from depth causing an increase in productivity directly leading to a positive excursion in 13Corg and the deposition of black shales (e.g. Handoh, 2003). Upwelling could also cause increased mixing as the upwelled water is replaced by intermediate or deep water from a diff erent location, in this case possibly the more radiogenic waters that bathed Blake Nose and/or the Pacific. Changes in trace metal abundances in black shal es from OAE2 exhib it signatures that are

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58 indicative of coastal upwelling (Brumsack, 2005) It has also been suggested that volcanic processes may have generated a buoya nt plume that initiated upwelling (Vogt, 1989). Work by Kolonic et al. (2005) supports th e theory that wind-driven upwelling is a mechanism for driving nutrient-rich waters to the surface to increase productivity. His recent work off the northwest coast of Afri ca found black shale formations interbedded with thin layers of carbonate sediment, sugge stive of oxic conditions, and attributes these lithologic changes to the alternating position of the Intertropical Convergence Zone (ITCZ). Movement of the ITCZ can cause peri ods of arid conditions when it is located at a more southerly position, followed by extremely humid conditions, when the convergence migrates to the north. This at mospheric driven oceanographic change is supported by modeling experiments across the CenomanianTuronian boundary (Flgel, 2002). A modeling experiment of a proposed Te thyan circumglobal current also predicts seasonal monsoonal events (Bush and Philande r, 1997). The modern analogue to this movement of the ITCZ is seen on the west coast of the African continent. During the northern hemisphere summer there are strong northerlies, which move the ITCZ north causing moist air to move inland over the continent. During the northern hemisphere winter the northerlies are weak, the ITCZ is in its more southern position, and dry air flows off the continent from the north leading to a more arid climate. When the ITCZ is in a more southerly position the weaker trades allow for upwelling along the coast. If this same idea is used on the South American con tinent there would be li ttle to no upwelling on the east coast when the ITCZ is in a mo re northerly position and enhanced upwelling when it is in a more southerly position. T oday, the movement of the ITCZ is a seasonal

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59 change, so it is difficult to us e this mechanism to explain a 106 year event. Kolonic (2005) invokes the idea of an orbital control on the location of the ITCZ 13C and Nd records are undoubtedly linked. Therefore, the mechanism for anoxia must combine both pro ductivity in the water column as well as enhanced intermediate to deep water mixing. Significantly, these data argue against the theory of stagnation as the cause for anoxia.

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60 CHAPTER 7 BACKGROUND ON EXTRACTION EXPERIMENTS Rutberg et al. (2000) first demonstrated that Nd extracted from extracted Fe-Mn oxide coatings was an effective tracer for ocean circulation on Pleistocene timescales. Their Nd isotopic record from a core in Cape Basin confirmed previous ideas that NADW production decreased during cold marine isotope stages stages 2 and 4 (e.g. Mix et al., 1985; Oppo and Fairbanks, 1987; Charle s et al., 1992). Their procedure designed to selectively extract the Fe-Mn oxide coa tings was modified from Chester and Hughes (1967) and used buffered acetic acid to rem ove the carbonate fraction followed by a 0.02 M hydroxylamine hydrochloride (HH) solution to reduce the Fe-Mn oxide fraction. Using this procedure Piotrows ki et al. (2004) developed th e record presented above to track millennial time scale changes in the st rength of NADW over the last 20 kyr (figure 2-3). The procedure used by Rutberg et al. (2000) was further te sted by Bayon et al. (2001) in a study of the Last Glacial Maximum (last 30 kyr) fr om a different core in the Cape Basin. This study was designed to isol ate the detrital fraction as well as the Fe-Mn oxide fraction of a marine sediment sample. Both of these fractions were then used to identify changes in ocean circulation. The continental sources of the detrital fraction provided information about the provenance of this material and possible water current directions, while Nd isotopes were extracted from the Fe-M n oxide fraction. A number of variations in the technique were developed in order to completely isolate the detrital and Fe-Mn fractions. These variations incl uded changes to the strength of the HH

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61 solution, heating the sample during extraction, and removing th e organic fraction prior to extraction. In the most effective procedure, an acetic acid wash was used to remove the carbonate fraction and a 0.5 M HH solution was used to remove the Fe-Mn oxide fraction, similar to Rutberg et al. (2000); however, they determined that using a HH solution with a lower molarity (0.04) did not remove the whole of the Fe-Mn oxide fraction and the Nd isotopic value of the detr ital fraction was shifted toward seawater values. Each variation on the extraction proc edure was systematically tested using Sr isotopes and REE patterns. It was assume d that the Nd isotopes were accurately recording the value of deep water when the Sr isotopes yielded appropriate seawater values. REE patterns of the various fractions are distinctly different and were used to verify whether the Fe-Mn oxide and detrital fraction were e ffectively separated from one another. This study was the first to system atically test the acetic acid wash and HH solution procedure. In conclusion, the detrit al fraction could be effectively separated from the Fe-Mn oxide portion, but it proved ve ry difficult to isolate the oxide portion with no effect from either the detritus, carbonate or the organic fractions.

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62 CHAPTER 8 RESULTS OF THE FE-MN OXIDE CO ATING EXTRACTION PROCEDURE AND VALIDITY TESTS 8.1 Variations on the Extraction Procedure The main goal of this portion of this project was to determine if it was possible to obtain Nd isotopic values from Fe-Mn oxide coatings that reflect seawater values on Cenozoic time scales. Bayon et al. (2000), Ru tberg et al. (2000), and Piotrowski et al. (2004) demonstrated that ex traction techniques are effect ive on younger timescales, but there is yet to be a systematic study of olde r sediments. To test the validity of the Nd isotopic values obtained from the extracted coatings in this study, they were compared to values from contemporaneous fossil fish te eth, assuming that the Nd isotopic value obtained from the fish teeth was correct. The extraction procedure by Rutberg et al. (2000) was the initial procedure used for this study, and it was subsequently modified. The main concern with any extraction pro cedure is the removal of material other than the desired Fe-Mn oxide coating. Contam ination from detrital material is likely to have an effect on the Nd value obtained, altering it toward more or less radiogenic values depending on the source. Detrita l in this case refe rs to any clay or other terrigenous material as well as any part iculate contamination from vol canic sources or hydrothermal processes. The first steps taken to minimize de trital contamination we re to alter the grain size used for extraction, the molarity of th e HH solution, and the length of the extraction time.

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63 The first variable tested was the grain si ze of the sediment. A previous study by Scher et al. (2003), on samples from ODP Site 1090, determined that extracting coatings from the <63 m size fraction in many cases did not give Nd values that fell within error of the values obtained from fossil fish teeth (Figure 8-1). The less than 63 m fraction is composed chiefly of clay material, and alt hough the particles may have oxide coatings, the chances of obtaining seawater values are greater if this possible contaminant can be eliminated. The 63-125 m and >125 m size fractions were also tested. A number of samples from each of those two size fractions were extracted and analyzed. It was determined that there was no distinguishab le difference between samples of 63-125 m and >125 m size fraction samples (Figure 8-1). Sa mples used in the remainder of this study consist of >63 m size fraction of sediment. -5 -4 -3 -2 -1 0 1 <63 63-125 >125 Sample Number Nd teeth coating Figure 8-1. The difference of Nd between fossil fish and Fe -Mn oxide coatings from samples of < 63 m (circles), 63-125 m (squares) and >125 m (triangles) size fractions. Samples with a difference less than 0.5 Nd units are assumed to agree within error for the TIMS.

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64 The other variable tested was the length of time the HH solution remained on the sediment. For this test all samples were extracted with a 0.5M HH solution. Work by Bayon et al. (2001) determined that 1M HH solution removed nearly all the Fe-Mn oxide coating on marine sediment, leaving the rema ining detrital material clean, which was their targeted material. By using a lowe r molarity HH solution, enough of the coating was removed for this study, but there was less chance of contamination from the remaining detrital material. Although the solu tion was weaker, an a dditional test was set up to determine whether it would have the same effect as the stronger solution if it were left on the samples for an extended length of time. To test this, sequential sediment samples were treated for 4, 2, and 1 hour time inte rvals. As figure 8-2 illustrates, samples treated for 1-2 hours fell within error of th e contemporaneous fossil fish teeth samples more often than samples treated for 4 hours. Several of the samples that were treated for 4 hours did not give Nd values that were close to the va lues obtained from the fish teeth. In these cases the HH solution must have re moved nearly all the Fe-Mn oxide coating and reacted with some of the detrital material, thus alte ring the isotopic signal towards more less radiogenic values indicating cont amination from a continental source. A possible source of this contam ination might be cations from exchangeable sites on the clays. As a result, samples used in this study were treated for 1.52 hours with a 0.5 M HH solution.

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65 -6 -5 -4 -3 -2 -1 0 1 2 4 hours 2 hours 1 hourNd teeth coatingSample Number Figure 8-2. Difference of Nd from obtained from fossil fish teeth and samples treated for 4 (diamonds), 2 (squares), and 1 (tri angles) hour extraction periods. 8.2 Results from Southern Ocean Sites Samples of fish teeth and Fe-Mn oxide coatings from 15-40 Ma (Miocene to Eocene) were analyzed from Sites 689, 690, and 1090 in the Southern Ocean (see figure 2-6 for site locations). The Nd values from fish teeth for Si te 689 range from -7.7 to -9.1 and values from Fe-Mn oxide coatings range from -7.7 to -9.7 (table 8-1). Out of 27 samples from Site 689 4 (15%) did not fall with in error of the fossil fish teeth (figure 83A); however, all coatings were less radiogenic than the teeth. The ages of samples from Site 690 range from 26 to 44 Ma (Oligocene to Eocene) with Nd values for teeth ranging from -8.7 to -10.2 (table 8-1). Values for th e coatings range from -8.2 to -10.5 and out of 23 samples 5 (~22%) values from oxide coatings did not fall within e rror of the fossil fish teeth (figure 8-3B). All but one of the samples that fell outsid e of error of the fish teeth was less radiogenic than the corresponding teeth value. Site 1090 teeth and coating

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66 samples range in age from 17-25 Ma (Miocene to Oligocene), Nd values from fossil fish teeth range from -7 to -8.3 and coating values range from -6.9 to -8.3 (table 8-1). Out of 17 samples all coating samples fell within error of Nd values obtained from fossil fish teeth (figure 8-3C). Thus, in the Southern Ocean 88% of the Nd values obtained from Fe-Mn oxide coatings fell within error of the values obtained from the fossil fish teeth. The greatest discrepancy between the extr acted coatings and fish teeth is 1.5 Nd units, and the average offset is 0.9 Nd units. -10.5 -10 -9.5 -9 -8.5 -8 -7.5 -7 202428323640 teeth Fe-Mn coatingNd(o)Ma689 A Figure 8-3 Nd(o) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings (red triangles) from the Southern Ocean Sites. A-689, B690, and C. 1090. Arrows on the plots for 689 and 690 highli ght the Fe-Mn oxide coatings that did not fall within e rror of the teeth.

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67 -9 -8.5 -8 -7.5 -7 -6.5 1618202224261090 teeth Fe-Mn coatingsNd(o)MaC Figure 8-3 A-C continued. -11 -10.5 -10 -9.5 -9 -8.5 -8 -7.5 2530354045690 teeth Fe-Mn coatingsNd(o)MaB -11 -10.5 -10 -9.5 -9 -8.5 -8 -7.5 2530354045690 teeth Fe-Mn coatingsNd(o)MaB

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68 Table 8-1. Nd isotopic values from Fossil Fi sh Teeth and Fe-Mn Oxide Coatings from Southern Ocean ODP Sites 689, 690, and 1090 Coatings2Teeth4Samplembsf Age (Ma)1143/144 Nd ( o ) 3143/144 Nd ( o ) 689B 689 7-6 1860.59017.910.51217-9.140.250.512188-8.780.31 689 7-6 12161.61018.230.512239-7.780.340.512213-8.290.31 689 8-1 84 63.34018.490.512217-8.220.250.512206-8.430.31 689 8-2 83.564.84018.690.512202-8.510.250.512179-8.950.31 689 8-3 465.54019.750.512157-9.380.700.512198-8.580.31 689 8-3, 12966.79020.110.512196-8.630.250.512195-8.640.31 689 8-3, 140 66.90024.790.512173-9.060.250.512187-8.790.31 689 8-5, 111.5 69.61025.320.51219-8.740.250.512187-8.790.31 *689 9-1, 26 72.36025.850.512165-9.220.250.512198-8.580.31 689 9-2, 7 73.67026.110.512170-8.640.510.512224-8.070.31 *689 9-3, 62.5 75.72026.510.512171-9.100.250.512219-8.170.31 *689 9-6, 6380.23027.130.512162-9.290.250.512233-7.900.31 689 10-3, 116.585.86527.910.512194-8.660.410.512186-8.820.27 689 10-5 2687.96028.200.512186-8.820.450.512221-8.140.27 689 11-2, 4693.26028.900.512155-9.420.410.512181-8.920.27 689 11-5, 10698.36029.510.512172-9.090.410.512203-8.480.27 689 12-2, 7.5103.92030.000.512183-8.880.410.512201-8.520.27 *689 13-1, 127.5111.88032.020.512181-8.9100.340.512220-8.160.27 689 13-2 107113.17032.300.512195-8.640.450.512203-8.490.27 689 13-4 82115.92032.890.512170-9.130.450.512202-8.510.27 689 13-6, 60118.70033.380.512223-8.100.410.512228-7.990.27 689 14-3, 104124.24034.710.51223-7.950.410.512246-7.650.27 689 14-4 82-88125.55035.000.512204-8.470.450.512227-8.020.27 689 15-4 45134.85036.050.512184-8.860.450.512207-8.400.27 689 16-3, 46142.86037.240.51222-8.160.410.512194-8.670.27 689 17-7 51-57158.64039.550.512165-9.230.450.512192-8.700.27 689 18-2, 60160.90040.070.512143-9.660.410.512173-9.060.27 690B 690 7-4,8354.20526.030.512167-9.190.250.512191-8.730.27 690 7-5,8757.24026.240.512163-9.260.250.512189-8.770.27 690 7-6, 3458.21026.340.512174-9.060.250.512191-8.720.27 *690 8-3, 12164.28027.440.512125-10.010.250.512157-9.380.27 690 8-4,6765.24027.560.512142-9.680.340.512156-9.410.27 690 8-5 1766.24527.690.512148-9.560.450.512157-9.380.25 690 8-6, 6768.24027.940.512173-9.080.410.512175-9.030.27 690 9-3, 14874.25528.780.512103-10.440.410.512131-9.880.27 *690 9-5 14877.25029.060.512122-10.070.450.512172-9.090.25 690 10-2, 13682.23029.720.51214-9.720.410.512139-9.740.27 *690 10-3 8783.24029.940.512106-10.380.450.512149-9.530.25 690 10-4, 13585.22530.570.512149-9.540.410.512138-9.760.27 *690 10-5 8486.21530.950.512220-8.150.450.512141-9.690.25 690 10-6, 3587.21531.330.512154-9.450.410.512151-9.490.27 690 11-1, 1889.25032.120.512147-9.580.250.512166-9.220.27 690 11-3, 1792.25033.270.512175-9.030.250.512175-9.020.27 690 11-4, 6894.25035.950.51219-8.750.410.512185-8.840.27 *690 11-5 1795.24036.220.512141-9.690.450.512183-8.880.25

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69 Table 8-1. Continued ______________________________________________________ 690 11-7, 1798.24037.110.512176-9.020.410.512143-9.650.42 690 11-7, 17 rep98.24037.110.512167-9.190.340.512143-9.650.42 690 12-1, 146100.23037.760.51216-9.330.410.512151-9.500.27 690 12-3, 146103.23038.750.512173-9.070.250.512183-8.870.27 690 12-6 94107.21041.880.512107-10.360.450.512131-9.900.25 690 12-7, 47108.24042.830.512128-9.940.410.512125-10.010.27 690 13-3, 74112.21044.180.51211-10.290.410.512115-10.200.27 1090 1090D 8-2, 13873.19016.310.512211-8.330.270.512212-8.310.27 1090D 8-3, 4873.79016.450.512224-8.080.270.512220-8.160.27 1090D 8-6, 38 78.19017.260.512242-7.730.270.512247-7.620.27 1090E 8-4, 133 80.08017.490.512227-8.020.270.512244-7.690.27 1090D 9-2, 582.98017.910.512229-7.980.270.512231-7.940.27 1090E 9-2, 137 87.98018.540.512246-7.650.270.512247-7.630.27 1090E 9-4, 48 90.09018.750.512237-7.830.290.512262-7.340.27 1090D 10-3, 593.98019.210.512218-8.200.290.512247-7.630.27 1090D 10-4,3595.78019.390.512250-7.580.290.512254-7.490.27 1090E 10-4, 3699.93019.800.512242-7.720.290.512239-7.790.27 1090D 11-3, 90103.93020.200.512265-7.270.290.512265-7.280.27 1090E 11-3, 122 108.23020.610.512278-7.030.290.512273-7.120.27 1090D 12-2, 130 112.33021.000.512286-6.860.290.512278-7.020.27 1090D 13-4, 39123.68022.450.512215-8.260.290.512223-8.090.27 1090E 13-3, 8125.89022.660.512213-8.300.290.512221-8.130.27 1090E 16-5, 116160.92024.880.512254-7.500.290.512239-7.780.27 1090D 17-3, 34163.12025.080.512258-7.420.290.512258-7.400.271. Ages for Site 689 from Mead and Hodell, 1995; Spiess, 1990; Shipboard Scientific Party, 1988. Ages for Site 690, Shipboard Scientific Party, 1988; and for Site 1090 are from Scher, 2006.2.143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and then normalized to Jndi-1 = 0.512103 (TIMS average).3. Fossil fish teeth data from Scher, 2005. Nd(o) = [(143Nd/144Nd)sample/(143Nd/144Nd)CHUR-1] x 104* indicates samples whose coating and teeth were not within error of one another. 8.3 Results from North Atlantic Sites Fish teeth samples and extracted coatings from contemporaneous sections were analyzed from North Atlantic DSDP Site 608 and ODP Sites 647 a nd 982. Due to the scarcity of teeth in samples from Site 608 only 2 samples were analyzed. The Nd values of the teeth from these two samples are -11.07 and -12.30. Coatings for both of these samples fall outside the error window at 9.66 and -11.28 respectiv ely (table 8-2 and figure 8-4). Four samples were analyzed from Site 647 and Nd values of the teeth range from -9.93 to -11.61, while Fe-Mn oxide coating values range from -9.66 to -11.28 (table

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70 8-2). All four of these samples fell within er ror of the contemporaneous fish teeth (figure 8-4). For all of the samples analyzed from these two sites the coating samples were consistently more radiogenic than the fish teeth samples. -12.5 -12 -11.5 -11 -10.5 -10 -9.5 5.566.577.588.59 608 coating 608 teeth 647 coating 647 teethNd(o)Ma 31.5 31 Figure 8-4 Nd(o) values from fossil fish teeth and Fe-Mn oxide coatings from DSDP Site 608 (circles) and ODP Site 647 (triangles ) from 5.5 to 9 and from 30 to 31 Ma. Twelve samples were analyzed from ODP Site 982 spanning from 9.2 to 14.4 Ma. Fossil fish teeth as well as phosphate pieces or fish debris (co mmonly bones or scales) were analyzed for three of the samples. The Nd values obtained from the two types of phosphates are indistinguishable, implying that when fish teeth are absent from a sample, phosphate fish debris can be used instead (table 8-2). The Nd values from the fish teeth and debris range from -8.13 to -10.86, and the oxide coating values range from -8.66 to 10.61, with all of the values falling within error of the teeth (table 9-2). In these samples the coating values are not consistently more or less radiogenic than th e teeth (figure 8-5).

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71 Of all the samples analyzed in the North Atlantic (all 3 localities) 88% of the values obtained from coating samples agreed with the values obtained for the teeth. -11.5 -11 -10.5 -10 -9.5 -9 -8.5 -8 -7.5 9101112131415 Fe-Mn coating teethNd (o)Ma 982 Figure 8-5. Nd(o) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings (red triangles) from ODP Site 982 from 9 to 15 Ma.

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72 Table 8-2. Nd isotopic values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from North Atlantic DSDP and ODP Sites 608, 647, and 982 Coatings 4 Teeth Samplembsf Age (Ma) 3 143/144 Nd Nd ( o ) 5 143/144 Nd Nd ( o ) 608 *608 17-1, 102.5152.0005.770.51206-11.280.380.512008-12.300.55 *608 20-2, 10.5177.3007.200.512143-9.6590.380.512070-11.070.27 647 647 13-1, 104 117.0107.700.512079-10.90.380.512049-11.480.27 647 13-1, 133 117.3007.940.512048-11.50.380.512043-11.610.31 647 13-2, 34.5 117.8158.360.512063-11.210.380.512044-11.590.27 647 17-1, 62 155.39030.400.512132-9.8640.380.512129-9.930.27 982 982 34-1 52.5A1307.1509.210.512105-10.400.450.512128-9.950.45 982 34-1 52.5B2307.1559.210.512105-10.400.450.512110-10.300.45 982 36-1 12326.3109.770.512118-10.140.450.512146-9.600.45 982 39-5 22.5A355.82510.630.512094-10.610.450.512081-10.870.45 982 39-5 22.5B355.82510.630.512094-10.610.450.512101-10.480.45 982 41-5 5.5B375.10311.200.512110-10.300.450.512126-9.990.45 982 43-3 103.5A394.20512.140.512187-8.800.450.512206-8.430.45 982 45-2 27.5B413.17512.640.512194-8.660.450.512221-8.130.45 982 47-1 62B432.26013.130.512130-9.910.450.512118-10.140.45 982 51-1 17.5A470.61514.130.512103-10.440.450.512089-10.710.45 982 51-1 1spiked470.61514.130.512103-10.440.450.512102-10.460.45 982 52-4 2spiked480.67514.400.512143-9.660.450.512112-10.260.451A samples are values from fossil fish teeth 2B samples are values from phosphate pieces, commonly fish debris such as scales or bone.3. Ages for Site 608 are from Ruddiman et al., 1987; for Site 647 Shipboard Scientific Party, 1987; and for 982 Shipboard Scientific Party, 1996.4. 143/144Nd values are normalized to the Jndi-1 average on the day the samples were analyzed and then normalized to Jndi-1 = 0.512103 (TIMS average)Nd(o) = [(143Nd/144Nd)sample/(143Nd/144Nd)CHUR-1] x 104* indicates samples whose coating and teeth values were not within error of one another. 8.4 Results from Cretaceous Samples As one final test, this extraction proce dure was performed on four samples from Cretaceous sediments (80-102 Ma) from ODP Sites 1050 and 1258. The Nd value for the fish teeth from the one sample from Site 1258 was -15.44 and the value from the coating was -16.05. From Site 1050 fish teeth values range from -5.00 to -8.44 and coating values range from -5.56 to -8.93 (table 8-3). The coating values of all four samples fell within error of the values obtained from the fish teeth and are not consistently more or less radiogenic than the teeth values (Figure 8-6).

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73 -16 -14 -12 -10 -8 -6 -4 7580859095100105 teeth Fe-Mn coatingsNd(t)Ma Figure 8-6. Nd(t) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings (red triangles) from ODP Sites 1258 and 1090 from 77 to 102 Ma. Table 8-3. Nd istopes from Fossil Fish Teet h and Fe-Mn Oxide Coatings from ODP Sites 1258 and 1050. Teeth2Coatings Samplemcd Age (Ma) 1 143/144 Nd Nd ( o ) 3Nd ( t ) 4 143/144 Nd Nd ( o ) Nd ( t ) 1258 38-1 105375.2080.000.511804-16.27-15.440.250.511815-16.05-15.220.45 1050 20-1 33490.6377.000.512179-8.95-8.440.250.512180-8.93-8.420.45 1050 29-2 102577.4699.730.512334-5.93-5.060.250.512353-5.56-4.690.45 1050 31-2 103596.65101.300.512337-5.87-5.000.250.512314-6.32-5.450.451. Ages for Site 1258 are from Erbacher, 2004 and for Site 1050 from Shipboard Scientific Party, 1998.2.143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and then normalized to Jndi-1 = 0.512103 (TIMS average).Nd(o) = [(143Nd/144Nd)sample/(143Nd/144Nd)CHUR-1] x 104 Nd(t) = [(143Nd/144Nd)sample(t)/(143Nd/144Nd)CHUR(t)-1] x 104 using 147Sm/144Nd 8.5 Tests of Validity Although a majority ~90% of the extracted Fe-Mn oxide coatings do fall within error of the contemporaneous fossil fish teeth, some do not and the scope of the next portion of the project was to determine whether there is a test other than analyzing fish teeth that could be used to identify coating samples with accurate Nd values. If successful, the goal

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74 was that these tests could be used in place of the more time consuming, complicated and expensive analyses of fossil fish teeth. Tests for the integrity of the coatings include REE plots, Sr isotopes, and major element ratios, which were all expected to detect possible contamination. 8.5.1 REE Plots REE plots for different geologi cal materials are very distinct; continental material, basalts, fish teeth, and Fe-Mn oxide coatin gs all produce unique R EE profiles. The goal was to determine whether the REE patterns fo r extracted coating samples that did not match the Nd value of the fossil fish teeth were dis tinct from those that did agree with the teeth data. 0.01 0.1 1 10Normalized sample/ PAASLa Ce Pr Nd Sm Eu Gb Tb Ho Yb Lu Figure 8-7. REE plot of four samples fr om ODP Site 690, two of the samples have Nd values that fall within error of contemporaneous fossil fish teeth (green triangles) and two do not (red circles). Samples are normalized to the initial sample weight and to PAAS (Taylor and McLellen, 1985).

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75 All of the REE plots from Fe-Mn oxide coati ngs for this study have a distinctive middle (M-) REE buldge, characterized by enrichment in the MREE and a depletion in the light (L-) REE and heavy (H-) REE. This is cons istent with analysis of REE from Fe-Mn oxide coatings from other studies (e.g. Bayon, 2002). To determine if REE patterns are different for extracted samples that fell within error of the fish teeth and those that did not, four samples were plotted from Site 690; two whose Nd values fell within error of the teeth and two that did not (figure 8-7). Both sets of samples have similar REE patterns, including MREE enrichment, character istic of Fe-Mn oxide coatings. There is, however, slight variability in the magnitude of the Ce anomalies. REE were analyzed from ex tracted coatings from a ll locations in this study, including the samples from the Cretaceous (tab le 8-4). The samples from each Site were averaged to get a REE pattern for each locati on. These results are plotted on figure 8-8. All the Sites have a MREE bulge and variable negative Ce anomalies. All samples have been normalized to the original sample weight as well as PAAS and, therefore, they do reflect relative concentrations. Samples fr om Site 690 and 689 in the Southern Ocean have the highest concentra tion, while the North Atlantic samples have lower concentrations of REE. In pa rticular, concentrations from Site 608 are about an order of magnitude lower than all other sites. The 4 samples analyzed from Cretaceous sediments from Sites 1050 and 1258 have concentrations that fall between the Southern Ocean and North Atlantic.

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76 0.001 0.01 0.1 1 10 647 608 982 Cretaceous 1090 690 689normalized samples/ PAASLa Ce Pr Nd Sm Eu Gb Tb Ho Yb Lu Figure 8-8. REE plot of the average values from extracted coatings from the North Atlantic Sites 608 (triangle), 647 (circl e), and 982 (square), the Cretaceous (Sites 1258 and 1050; (box with x), and the Sout hern Ocean Sites 1090 (diamond), 690 (cross) and 689 (triangle). REE are normalized to PAAS (Taylor and McLellen, 1985) a nd initial sample weights.

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77 Table 8-4 REE values from Fe-Mn Oxide Coatings. SampleLaCePrNdSmEuGdTbHoYbLu North Atlantic 608 608 17-1 102.50.0170.0050.0160.0170.0190.0220.0240.0230.0210.0160.014 647 647 3-1 1040.0630.1050.1290.1610.2670.3170.3250.3030.2260.1600.145 647 13-2,34.50.0380.0700.0800.1010.1710.2000.1990.1800.1320.0960.088 982 982 34-1 52.50.2160.0820.2500.3300.4110.4710.5550.5080.4460.3240.268 982 36-1 90.0350.0200.0640.0830.1310.1400.1540.1200.1000.0800.028 982 41-5 3-80.0570.0300.0940.1270.1950.2160.2360.1920.1560.1180.078 982 43-3 103.50.1800.0780.2050.2730.3540.4130.4810.4350.3970.3150.270 982 45-2 280.0530.0320.0840.1110.1720.1840.2040.1650.1500.1340.084 982 47-1 1620.0310.0150.0480.0570.0880.0990.1040.0750.0780.0750.023 982 51-1 17.50.3340.1880.4010.5110.6280.7030.8180.7120.6220.4870.409 982 52-4 27.50.1830.0890.1900.2390.2930.3220.3940.3470.3480.3010.252 Average NA0.1010.0600.1320.1700.2310.2600.2950.2560.2250.1780.135 Southern Ocean 689 689 10-3 86.51.1620.4781.2571.6572.0592.2022.6922.5572.4152.1742.345 689 10-5 261.1250.3311.3741.8532.3242.5803.0222.7772.3761.6731.696 689 13-1 127.50.4660.1380.4710.4870.5840.6510.6520.7080.6970.7130.647 689 13-2 1040.4040.1570.4930.6240.7930.8861.0150.9980.9100.8100.766 689 13-4 820.2640.0730.3640.4910.6480.7330.8470.7740.6590.4800.455 689 13-6 600.4380.0860.3750.3740.4240.4910.4460.5540.6120.6610.600 689 14-4 850.9640.3751.0741.4001.7001.9532.2602.1751.9791.5971.607 689 15-4 450.7860.3200.9401.2461.5531.7562.0161.9051.6681.2371.240 689 16-3 460.3520.0790.2390.2160.2180.2490.2280.2770.3320.4130.367 689 17-6 610.4010.1370.2830.2690.2840.3340.2900.3580.4510.5560.526 689 17-7 540.7480.2850.8631.1561.4151.6141.8691.7301.5361.1181.117 689 18-2 600.2530.0820.1420.1200.1070.1270.1050.1270.1950.2890.273 Average 6890.5710.1950.6130.7680.9401.0561.1971.1581.0720.9090.902 690 690 8-4 660.7020.2171.0351.1111.4501.4831.6721.6401.3821.2401.091 690 8-5 141.0880.3721.2721.6041.9712.0802.4222.3642.0971.8571.923 690 9-3 1480.1010.0390.1470.1650.2170.2300.2580.2410.2090.1710.156 690 9-5 147.51.3550.7701.7212.2242.7432.9843.3463.0602.5381.9061.909 690 10-5 840.8350.6251.1081.3801.8141.9302.1652.1731.8331.7581.834 690 11-5 16.51.5290.9081.8122.4883.0383.4943.9503.4262.8251.7831.825 690 11-7 170.0210.0080.0230.0260.0310.0340.0410.0360.0340.0250.023 690 11-7 17rep0.2350.0500.3260.3650.4690.5050.4970.4960.4030.2680.222 690 12-6 940.4000.4060.6430.8801.2431.3941.4831.3921.1120.8450.804 690 12-7 470.1080.0660.1750.1950.2720.3070.2560.2620.1910.1270.099 690 13-3 240.0290.0210.0360.0400.0490.0530.0620.0570.0520.0350.031 Average 6900.5820.3160.7540.9531.2091.3181.4681.3771.1530.9110.901 1090 1090 12-5 112.50.2050.1280.2670.2510.3120.3180.3880.3590.3060.3460.300 Error is 5%.

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78 8.5.2 Strontium Isotopes Strontium has a long residence time in the ocean, thus the Sr isotopic value of the ocean is homogeneous at any one time in earth s history. The assumption is that if the coatings incorporate the ocean water chemis try of the overlying wa ter mass the coating should incorporate the Sr isot opic value as well as the Nd isotopic value of the water mass at that time. Other studies that utili zed Fe-Mn oxide coatings as archives for Nd, such as Piotrowski et al. (2004) used Sr isotopes as a tool fo r evaluating the integrity of the measured Nd value. Sr isotopes were measured on a number of the extracted coatings in this study (table 8-5). These values were compared to 87Sr/86Sr values obtained from foraminifera from the same sediment sample, which are as sumed to represent the seawater value. Because seawater 87Sr/86Sr changes with age, the samples have been plotted on the seawater Sr isotope curve (figure 8-9). They have been divided into two groups; extracted coatings whose Nd values fell within error of the Nd value of the teeth and those that did not. All of the samples either fell on the Sr curve or were more radiogenic than the curve. There is some correlation between sample lo cations and Sr isotopic values. All of the samples from the North Atlantic lie on the curve, while the Southern Ocean samples are mixed. The North Atlantic samples are also younger than the Southern Ocean samples, ~10-13 Ma and younger versus 19.5 Ma and older. There is, however, no correlation between the ages of the Southern Oc ean samples that fell on and off the curve. Interestingly a replicate sample (37.0 Ma) yiel ded two very different Sr isotopic values,

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79 one fell on the Sr curve and one did not even though the Nd isotopic values for the both coatings were valid. 0.7076 0.7078 0.708 0.7082 0.7084 0.7086 0.7088 0.709 0.7092 01020304050 87/86Sr curve error + error leachate within error of teeth leachate outside of error of teeth87Sr/86SrMa Figure 8-9. Seawater Sr curve over the pa st 50 Ma (Woodruff and Hodell, 1994; Mead and Hodell, 1995; Farrell et al., 1995; Martin et al., 199 9) plotted with 87Sr/86Sr values from extracted Fe-Mn oxi de coatings. Green triangles are from extracted coatings whose Nd value fell within error of the values measured from fossil fish teeth and th e red boxes are from extracted coatings whose values fell outside of error of those obtained from the teeth. The 87Sr/86Sr error bars are smaller than the symbols.

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80 Table 8-5. 87Sr/86Sr values from Extracted Material and Foraminifera from Samples from ODP Sites 689, 690, 982, and 1090 CoatingsForaminifera SampleAge (Ma)87/86Sr 287/86Sr 3Nd within error of teeth 689 8-3 12920.110.7083710.0000230.7084250.000023 689 8-3, 419.750.7084500.0000230.7084700.000023 689 10-5 2628.200.7081330.0000230.7080450.000023 689 13-2 107.531.000.7079400.0000230.7079600.000023 689 13-4 8232.890.7078950.0000230.7078550.000023 689 14-4 8535.000.7077940.0000230.7077400.000023 689 15-4 4536.050.7077720.0000230.7077600.000023 689 17-7 5439.790.7077730.0000230.7077250.000023 690 8-4, 66.527.560.7085370.0000230.7080750.000023 690 8-5 1727.690.7082590.0000230.7080330.000023 690 9-3, 14828.780.7082630.0000230.7080090.000023 690 11-1, 17.532.120.7082350.0000230.7078860.000023 690 11-7, 1737.110.7078240.0000230.7077350.000023 690 11-7, 17 rep37.110.7076880.0000230.7077350.000023 690 12-6 9441.880.7079710.0000230.7077700.000023 690 12-7, 4742.830.7079140.0000230.7078310.000023 982 34-1 52.510.800.7088640.0000230.7088550.000023 982 36-1 1210.050.7088470.0000230.7088750.000023 982 39-5 22.511.380.7088130.0000230.7088400.000023 982 41-5 5.511.440.7088020.0000230.7088350.000023 982 45-2 27.513.320.7087800.0000230.7087850.000023 1090 12-3, 7021.510.7083230.0000230.7083540.000023 Nd outside of error of teeth 689 13-1, 124.532.020.7080110.0000230.7079200.000023 690 9-5 147.529.060.7081600.0000230.7080050.000023 690 10-5 8430.950.7081030.0000230.7078990.000023 690 11-5 16.536.220.7081940.0000230.7077240.0000231. Ages for 689 from Mead and Hodell, 1995; Spiess, 1990; Shipboard Scientific Party, 1988. Ages for 690 from Shipboard Scientific Party, 1988. Ages for 982 from Shipboard Scientific Party, 1996. Ages for 1090 from Scher, 20062. Measured 87Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (2 ). and normalized to 86Sr/88Sr = 0.1194.3. Sr values from 689, 690, and 1090 from Scher et al., 2005. 8.5.3 Major Element Ratios When Nd values of the coating do not match with fossil fish teeth values, the assumption is that the fish teeth value is correct and the value obtained from the extracted Fe-Mn oxide coating has been contaminated by detrital Nd. The source of this Nd is most likely clay or terrigenous material that has a non-seawater Nd value. To further test

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81 this theory major element ratios were measur ed on a number of the extracted samples. Al, Na, K, and Ti, some of the common elements in clays, were ratioed against Fe plus Mn, the main elements in coatings. Iron and Mn were added together to account for the high variability seen in the con centrations between the two elem ents at various locations. The assumption was that for samples with distinct extracted coating and fish teeth Nd values the elemental ratios might reflect an in crease in the elements contributed from the clays. Elemental ratios were analyzed for 44 samples from Southern Ocean, North Atlantic, and the Cretaceous Site s. For 7 of these samples the Nd values of the teeth and coatings did not match (table 8-6). Ti/( Fe+Mn) ratios range from 0.001 to 0.036 and there is no discernable correla tion between ratios for extracte d coatings whose values fell within error of the teeth and those that did not; in fact the highest values correlate to samples with matching coating and fish teeth values, while samples with distinct coating and fish teeth Nd isotopic values record some of the lowest Ti/(Fe+Mn) values (figure 810). This lack of correlation is also seen in the other major element ratios; Mg/(Fe+Mn), Al/(Fe+Mn) and K/(Fe+Mn).

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82 00.0050.010.0150.020.0250.030.0350.04 -2 -1.5 -1 -0.5 0 0.5 1 1.5 647 within 689 within 690 within 982 within 1090 within Cret. within 608 ouside 689 ouside 690 outside Ti/(Fe+Mn) Nd teeth-coatings Figure 8-10 Ti/(Fe+Mn) ratios of samples vs. the difference between Nd values of the fossil fish teeth and the coatings from Sites 608, 647, 689, 690 982, 1090, and the Cretaceous samples from Sites 1050 and 1258. For Sites 608, 647, 689 and 690 the red symbols represent those samples whose Nd values for the teeth and the coatings did not match, while blue symbols throughout represent samples whose Nd values for the teeth and the coatings did match.

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83 Table 8-6. Major Element Rations from Site 608, 647, 690, 1090, and 1258________ SamplesAl/Fe+MnMg/Fe+MnTi/Fe+MnNa/Fe+MnK/Fe+Mn Nd teethNd coating 647 13-1 1041.1670.4970.0022.3760.851-0.58 647 13-2 351.1540.5580.0017.1580.829-0.37 689 8-1 841.1170.1890.0031.7650.319-0.21 689 8-3 41.3450.1330.0012.8830.5100.79 689 8-3 1400.7300.2700.0014.0350.1970.27 689 10-5 260.0890.0460.00212.9710.0260.67 689 13-2 1081.8580.4680.1221381.9501.1130.15 689 13-4 822.4430.7890.064835.9281.2830.62 689 13-6 600.5122.8840.0025.1860.310-0.06 689 14-4 8510.0200.6940.2383783.4267.0010.44 689 15-4 456.9641.5780.0041104.5721.0310.45 689 16-3 460.2102.6340.0023.5830.095-0.51 689 17-7 541.2081.1200.013678.6240.5730.53 689 18-2 600.0352.3930.0013.4070.1640.60 690 8-4 660.0630.0620.0000.1420.0160.28 690 8-5 170.0640.0570.00115.1920.0210.18 690 9-3 148 0.0510.0500.0000.1280.0260.55 690 11-7 170.1780.5540.0090.6840.070-0.64 690 11-7 17 rep0.0670.1000.0120.7740.058-0.47 690 12-7 471.5560.5990.0365.1130.665-0.07 690 13-3 740.5342.3120.0165.6140.2590.09 982 34-1 530.2600.1280.01914.8460.1210.45 982 36-1 120.3800.1620.0041.2770.0680.55 982 39-5 230.9180.4560.0096.7110.2820.14 982 43-3 1040.3240.0630.0042.2290.1130.37 982 45-2 280.4250.1280.0021.6700.0670.53 982 47-1 1620.5250.2520.0061.7300.151-0.23 982 41-5 5.50.6800.1550.0022.1000.1360.31 982 51-1 17.50.2520.0360.0165.0790.091-0.27 982 52-4 27.50.5110.1630.02431.5950.519-0.60 1090 13-1 251.4190.3560.0013.1200.4040.28 1090 31-4 341.2060.6890.0014.2330.4880.14 1050 20-1 331.6010.4830.00661.8661.372-0.02 1050 29-2 1020.0360.0410.0000.2000.013-0.37 1050 31-2 1030.0130.0130.0000.0780.0230.45 1258 38-1 1050.4720.3650.0027.4210.162-0.22 *608 17-1 1030.0890.4220.0015.4670.081-1.02 *689 9-1 261.8060.1760.0022.9540.5970.64 *689 9-6 633.6300.1090.0026.0870.7291.39 *689 13-1 1280.7903.9390.0065.3890.4120.76 *690 9-5 1480.0160.0320.0012.9210.0160.98 *690 10-3 870.0300.0530.00210.8060.0190.84 *690 10-5 840.0820.0590.00120.3210.024-1.54 *690 11-5 170.0090.0450.0012.6000.0090.82 indicates that teeth and coatings values do not fall withing error of one another.

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84 8.5.4 Sequential Extraction Procedure Results As a final test for the extracted coatings a sequential extraction and dissolution procedure was performed. The method for ex traction (Bayon et al., 2002) was slightly different than the extraction method for the sing le extracted samples. The purpose of this sequential extraction experiment was to determ ine the Sr and Nd isotopic values, the Nd concentrations, and the REE pa tterns for the various fractions of a given sample including the carbonate, Fe-Mn oxide coa ting, and residual fractions. Using this extraction technique the Nd value of the Fe-Mn oxide coatings consistently fell within error of the value for the fossil fish teeth (figure 8-11) even for the samples from Site 608, which previously yielded coatings with values that were too radiogenic. The Nd value from the carbonate fraction fa lls within error of the teeth and coatings for 5 out of the 8 samples, and is not consistently more or less radiogenic for those samples that fall outside of error. The Nd value from the residual fraction does not fall within error of the fish teeth for 6 out of the 8 samples, and they are consistently less radiogenic (table 8-7). Sr isotopes were also measured from the th ree separate sediment fractions from the sequential extractions (table 8-8). The carbona te fraction values fall within error of the seawater value for six out of the seven sa mples. For sample 647, 13-4 the carbonate value is less radiogenic than seawater by 0.000455 (figure 8-11B). The Fe-Mn oxide coating values either fall within error or ar e more radiogenic than the seawater value. The residual fractions for five of six samples are more radiogenic than seawater values. For 982 47-1 all four fr actions yield the same 87Sr/86Sr value.

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85 -15 -14 -13 -12 -11 -10 -9 -8 teeth carbonate Fe-Mn oxide residualNd (o) A 0.708 0.71 0.712 0.714 0.716 0.718 0.72 0.722B seawater carbonate Fe-Mn oxide residual87Sr/86Sr608 647 689 689 690 690 982 982 21-5 13-4 13-2 15-4 10-5 9-5 34-1 47-1 Figure 8-11. Nd(o) and 87Sr/86Sr values from 8 sequential extraction samples A) Nd(o) values from 8 sequential extraction sa mples. Sample 690, 9-5 does not have an Nd(o) value for the carbonate. B) 87Sr/86Sr values from 8 sequential extraction samples, errors are smaller than the data points. Each sample represents 4-5 cm from th e core sample indicated. Sample 690, 9-5 does not have an 87Sr/86Sr value for the carbonate fr action and samples 608, 21-5; 689, 13-2; 689, 154; and 690, 9-5 do not have values for the residual fraction. Seawater values from Hodell and Woodr uff, 1994; Farrell et al., 1995; Mead and Hodell, 1995; Martin et al., 1999.

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86 Table 8-7. 143/144Nd values for Fossil Fish Teeth, Carbonate, Fe-Mn Oxide Coatings, and Residual Fractions from the Sequential Extraction Samples Teeth1CarbonateFe-Mn OxideResidual 143/144 Nd Nd(o) 2 143/144 Nd Nd(o) 143/144 Nd Nd(o) 143/144 Nd Nd(o)608 21-5 0.512585-10.280.320.512090-10.690.450.512097-10.550.320.512070-11.080.32 647 13-40.512583-10.790.320.512055-11.370.450.512117-10.160.320.511921-13.990.32 689 13-2 0.512594-8.490.270.512176-9.010.450.512199-8.560.320.511936-13.690.32 689 15-4 0.512595-8.400.270.512214-8.270.450.512190-8.740.320.512162-9.290.32 690 10-5 0.512588-9.690.270.512015-12.150.450.512122-10.070.320.511948-13.460.32 690 9-5 0.512591-9.090.270.512144-9.640.320.512031-11.840.32 982 34-10.512585-10.300.450.512128-9.950.450.512108-10.340.320.512016-12.130.32 982 47-1 0.512586-10.140.450.512090-10.690.450.512122-10.070.320.512111-10.280.321. Measured 143Nd/144Nd of the Jndi-1 standard = .512102 0.000014 (2 ).Nd(o) = [(143Nd/144Nd)sample/(143Nd/144Nd)CHUR-1] x 104 Table 8-8. 87Sr/86Sr Values for Seawater Carbonate, Fe-Mn Oxide Coatings, and Residual Fractions from the Sequential Extraction Samples Seawater Carbonate 1 Fe-Mn OxideResidual87Sr/86 Sr87Sr / 86 Sr87Sr / 86 Sr87Sr/86 Sr 608 21-5 0.7089204.6E-050.7089540.0000230.7089150.000023 647 13-40.7088554.6E-050.7084000.0000230.7086860.0000230.7226910.000023 689 13-2 0.7079054.6E-050.7078740.0000230.7083230.000023 689 15-4 0.7077604.6E-050.7077370.0000290.7078760.000023 690 10-5 0.7079704.6E-050.7079380.0000230.7084040.0000230.7182670.000023 690 9-5 0.7080354.6E-050.7083600.000023 982 34-10.7087904.6E-050.7089190.0000230.7089220.0000230.7182590.000023 982 47-1 0.7088754.6E-050.7088090.0000230.7089060.0000230.7088220.0000231. Measured 87Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (2 ). REE patterns from the three sediment fracti ons were also analyzed from each of the extracted samples (table 8-9). Below ar e the plots for these REE patterns grouped by site (figure 8-12, A-D). In all cases the concentration of the residual fraction is an order of magnitude or more greater than the oxide coating fraction and the carbonate fraction (figures 8-13A-C). The residual fraction from all samples except for 647, 13-4 and 982, 34-1 have patterns similar to those of the coatings, having a MREE bulge. In contrast, sample 647, 13-4 is LREE enriched and sample 982, 34-1 has a very flat pattern similar to that of shale. Interest ingly, both 689 samples and 690, 19-6 have a large Eu anomaly. The anomaly is also seen in the carbonate fr action of these samples. The REE patterns for all of the oxide coatings have the dis tinctive MREE bulge indi cative of Fe-Mn oxide coatings and, except for sample 647, 13-4, a ll of the coating sa mples exhibit a Ce depletion. The carbonate fraction in all cases has the lowest concentrations (figure 8-13

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87 A-C). The carbonate fraction patterns for samples from 689, 690, and 982 all have patterns that are similar to the seawater REE pattern, while the carbonate patterns from both Sites 608 and 647 have a slight MREE bulge. 0.001 0.01 0.1 1 10 608 21-3 res 608 21-3 ox 608 21-3 carb 647 13-4 res 647 13-4 ox 647 13-4 carb seawaternormalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuA 0.001 0.01 0.1 1 10 689 13-2 res 689 13-2 ox 689 13-2 carb 689 15-4 res 689 15-4 ox 689 15-4 carb seawaternormalized sample/ PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuB

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88 0.001 0.01 0.1 1 10 690 9-5 res 690 9-5 ox 690 9-5 carb 690 10-5 res 690 10-5 ox 690 10-5 carb seawaternormalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuC 0.001 0.01 0.1 1 10 982 34-1 res 982 34-1 ox 982 34-1 carb 982 47-1 res 982 47-1 ox 982 47-1 carb seawaternormalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuD Figure 8-12 REE patterns from 8 sequentia l extractions. (A) S ites 608 and 647, (B) 689, (C) 690, and (D) 982 for 3 different sedime nt fractions; the residue (res), the Fe-Mn oxide coating (ox) and the carbona te (carb). Also included is the REE pattern for modern seawater fr om 3000m (De Baar et al., 1985).

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89 0.001 0.01 0.1 1 10 seawater 689 13-2 res 982 34-1 res 690 10-5 res 608 21-3 res 647 13-4 res 982 47-1 res 689 15-4 res 690 9-5 resnormalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuA 0.001 0.01 0.1 1 10normalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuB

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90 0.001 0.01 0.1 1 10normalized sample / PAASLa Ce Pr Nd Sm Eu Gd Tb Ho Yb LuC Figures 8-13 REE patterns for 3 sediment fractions for sequential extractions. REE patterns for A) the residual fraction, B) Fe-Mn oxide coating fraction, and C) the carbonate fraction from the sequentia l extraction samples from sites 608 and 647, 689, 690, and 982 showing the re lative concentrations of each fraction group. Table 8-9. REE Values from Sites 608, 647, 689, 690, and 982 from Three Sediment Fractions SampleLaCePrNdSmEuGdTbHoYbLu 608 21-3 res10.0590.0350.0680.0910.1050.1150.1220.1130.0930.0600.057 647 13-4 res0.2320.3400.2140.2370.2230.2190.2180.1690.1150.1120.112 689 13-2 res0.0400.0260.0370.0450.0490.1790.0590.0530.0490.0480.049 689 15-4 res0.0340.0160.0310.0390.0450.2860.0580.0470.0420.0350.034 690 9-5 res0.0790.0380.0890.1140.1290.1280.1400.1290.1060.0880.089 690 10-5 res0.1730.1320.1690.2080.2290.4900.2620.2420.2160.2200.223 982 34-1 res0.0130.0090.0110.0130.0140.0150.0150.0140.0130.0130.014 982 47-1 res0.0190.0080.0160.0210.0240.0290.0320.0300.0320.0270.028 608 21-3 ox20.0700.0290.0440.0500.0470.0520.0510.0660.0570.0540.050 647 13-4 ox0.3370.6300.4230.5470.7010.8290.7900.7650.6180.5290.520 689 13-2 ox0.6320.2430.6510.8861.0731.2231.3541.3111.2641.0951.085 689 15-4 ox0.7280.2830.8041.1001.3381.5341.6741.5561.4241.0991.072 690 9-5 ox2.4180.6883.1264.1145.1305.1235.9575.4304.5023.4423.406 690 10-5 ox1.8481.2012.0912.6873.3363.4363.8823.7523.3963.2363.313 982 34-1 ox0.3170.1090.2660.3710.4270.5070.6030.5640.5870.4590.482 982 47-1 ox0.2250.0780.1910.2670.3120.3730.4410.4090.4290.3390.355 608 21-3 carb30.0310.0130.0210.0270.0290.0350.0390.0420.0410.0410.043 647 13-4 carb0.0620.0910.0850.1200.1640.1760.1870.1880.1520.1170.122 689 13-2 carb0.0340.0120.0190.0220.0250.0810.0320.0380.0470.0880.098 689 15-4 carb0.0630.0250.0360.0440.0470.1030.0590.0720.0820.1390.148 690 9-5 carb0.0880.0390.0680.0870.1050.1160.1220.1350.1380.1650.191 690 10-5 carb0.0260.0230.0130.0150.0160.1060.0220.0250.0300.0630.080 982 34-1 carb0.0310.0070.0180.0210.0230.0300.0320.0350.0390.0510.054 982 47-1 carb0.0310.0080.0170.0200.0220.0290.0270.0300.0340.0480.0541. residue fraction 2. Fe-Mn oxide fraction 3. carbonate fraction Error is 5%.

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91 CHAPTER 9 DICUSSION OF EXTRACTION RESULTS FROM THE SOUTHERN OCEAN; NORTH ATLANTIC; AND CRETACEOUS AGE SAMPLES With almost 90% success the extraction pro cedure applied to the samples in this study effectively removed a deep water Nd signal with the Fe-Mn oxide coating fraction of the marine sediments, and recorded N one of the tests of validity, Sr isotopes, REE patterns, nor major element ratios allowed one to distinguish extracted samples that recorded deep water isotopic values correctly from those that did not when compared to Nd values obtained from fossil fish teeth. Yet, by experimenting with these variables much more was learned about extraction thes e coatings and the composition of marine sediments. 9.1 Possible Lithologic Effects on the Extraction Procedure In the Southern Ocean nearly 90% of all samples analyzed fell within error of the contemporaneous fossil fish teeth (figure 8-3A-C ). All but one of the coating values that were not within error of the fish were le ss radiogenic than the value from the teeth indicating that these samples ha ve been influenced by terrigenous material. This was the primary concern for this extraction project and it appears that in several cases associated sediment contaminated extracted coatings. Although the lithology at each of the three S outhern Ocean sites consists primarily of carbonate sediments, there is some variati on in the amount of ca rbonate, terrigenous material, and opal. Figure 10-1 shows th e weight percent of opal, carbonate and terrigenous material for samples from 19 to 25 Ma at Site 1090 (detailed lithological data

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92 is not available for the other sites). They are plotted against the difference between Nd values obtained from fossil fish teeth and Fe -Mn oxide coatings. For all of the samples these two values plot within error, even though the lithologies demonstrate a wide range of compositions. This illustra tes that the extractio n method is effective over a wide range of compositions. -0.4 -0.2 0 0.2 0.4 0.6 01020304050 wt% opal 020406080100 wt% carbonate 020406080100 wt% terrigenous Figure 9-1. Weight percent opal, carbonate, and terrigenous material from Site 1090 from 19.2 to 25.1 Ma plotted against the difference between Nd values from fossil fish teeth and Fe-Mn oxide coatings. A pl ot of 0 indicates the values were the same. Lithologic data from Diekmann, 2004. In the North Atlantic samples from Sites 647 and 982 produced excellent agreement between fish teeth and oxide coatings (figures 8-4 and 8-5) ; however, for Site 608 the Nd values for all of the coating were mo re radiogenic than the values obtained from the fish teeth (figure 8-4). This implies a consistent source of contamination that was attacked by the HH solution. A potentia l radiogenic source of Nd in the North Atlantic could be effects from the mid-ocean ridges (Frank et al, 2006). Of the sampled sites Site 608 is located closest to the ridge system, on the flank of the Kings Trough. It

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93 has been shown that Nd in hydrothermal fluids is removed by oxide and sulfide precipitates very close to the ridge (Michard et al., 1983; Ge rman et al., 1990). However, even if there were an effect from hydrotherm al sources we would expect it to also affect the Nd value of the fish teeth, altering them in the same manner as the coatings. 9.2 REE Patterns of Fe-Mn oxide coatings The purpose of analyzing REE patterns for the extracted coating samples was to determine whether the coatings had been co ntaminated by 1) a de trital source, which should produce a flatter REE profile because the samples are normalized to PAAS, or 2) a hydrothermal source, which should produce a heavy REE (HREE) enrichment (figure 8-7). There is no difference in the REE patterns for extracted coating samples in which the Nd value from the coating agreed with the fi sh teeth value and thos e that did not. The patterns for these four samples are very sim ilar, with the distin ct MREE bulge common to oxide coatings. This suggests that REE profiles do not provide a mechanism to identify contaminated samples. There is a slight difference in the Ce anomalies between the two sets of samples in figure 8-7. Although there is much debate on the topic, Ce anomalies are believed to reflect redox conditions at a given location (e .g. Wright et al., 1987; Lcuyer et al., 2004). In most cases there is a very distinct nega tive Ce anomaly for the samples in this study, suggesting that the sites were influen ced by oxidizing conditions. Although the Ce anomalies shown in figure 8-7 are variable, the samples noted as falling outside of error represent the two extremes w ith the largest and smallest observed Ce anomalies. Assuming that the magnitude of the Ce anom aly reflects the extent of the oxidizing

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94 conditions, this pattern suggests that reduci ng versus oxidizing conditions do not affect the Nd values of the extracted coatings. Although the REE plots do not distinguish between samples with similar fish tooth and coating Nd isotopic values and those with distinctly different values (figure 8-7), the averages for different locations record sl ight differences (figure 8-8). The most noticeable difference between the various sites is the relative concentrations. There is very little information known about the minera logy of the Fe-Mn oxide coatings and one of the major questions a bout this material is whether it is an open system that can be influenced by the composition of pore waters. If these coatings were an open system with respect to REE, it could be expected that the concentrations of REE in the coatings might increase or decrease as the sediments aged, acquiring or loosing REE into the pore waters. However, the extracted coatings from the Cretaceous (~90Ma) do not have higher or lower concentrations than the younger sediments (figure 8-8). The relative concentrations are not due to the length of burial time, but could be due to the sedimentation rates at the various sites. Ta ble 9-1 shows the average sedimentation rate at the sampled sites along with the appr oximate Nd concentration from the REE measurements. There is a general correlati on between the concentration of Nd and the sedimentation rate; the higher the sedimentation rate the lower the concentration of Nd (figure 9-2). This is reflected in the R EE analyzed from the single extracted samples (figure 8-8) and the REE plots from the oxide fraction of the sequential extraction samples (figure 8-13B) also s upport this conclusi on. Using both analytical methods samples from Sites 608, 647, and 982 have the lo west concentrations, while those from Sites 689 and 690 have the highest.

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95 0 5 10 15 20 25 30 35 0510152025303540[Nd]m/m.y. Figure 9.2. Average sedimentation rate versus Nd concentration for Sites 608,647, 982, 689, 690, 1090, and 1258. Line represents the best fit line. 9.3 Sr Isotopes Sr isotopes were measured from the extracted Fe-Mn oxide coatings and although samples that yielded the same Nd value as the contemporaneous fsih teeth fell both on the seawater curve and above it (more ra diogenic), the four samples whose Nd value did not match the teeth value all were more radiogenic than the Sr seawater curve (figure 8-9). This suggests that these samples have been contaminated by terrigenous material that affected the Sr as well as the Ns isotopic valu es. Since the Sr isotopic values for most of the residual sediment fraction were more radiogenic than th e coatings (as measured from the sequential extraction samples (figure 8-11), implying a continental origin, it is safe to conclude that there is some contamination fr om the sediments that affects the Sr isotopic values of the extracted coatings. In a number of samples the Sr isotopic va lues of the extracted coatings were affected by the associated terrigenous sediment in the sample, but the Nd isotopic values were not. This phenomina is most likely due the particle reaction, as Nd is much less Table 9-1. Site Locations with Average Sedimentation Rate and Average Nd concentration in coatings Site average sed.1average 2rate (m/m.y.)[Nd] ppm 608340.54 647164.19 982356.26 68954.91 6905.530.48 1090108.04 1258314.131 from Initial Reports for each Site2 from REE analysis

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96 particle reactive than Sr. The distribution coe fficient in Nd is lower and therefore there is less Nd in the pore waters when compared to Sr. Due to pore water mixing Sr is then more variable throughout the sediments. Martin and Scher (2004) measured Sr is otopic values of fossil fish teeth and determined that these values were commonly less radiogenic than associated foraminifera and the Sr seawater curve. This was interpreted to represent the addition of pore water Sr derived from recrystallization of older carbona tes into the apatite of the teeth, indicating that this apatite is not a closed system with respect to Sr. Unlike the teeth, all of the extracted samples either fell on the Sr curve or were more radiogenic, suggesting that the coatings are not influenced by pore water diag enesis or the input from the contaminant overwhelms the diagenetic signal. The radiogenic Sr values in the extracted coatings argue that the source of the contamination is derived from contamination from terrestrial material during sample preparation. Piotrowski et al. (2004 and 2005) used 87Sr/86Sr values to identify extracted Fe-Mn oxide coatings with accurate Nd isotopic values They measured the Sr isotopic values of all the extracted samples and only accepted the Nd values from samples with 87Sr/86Sr that fell on the seawater Sr curve for the appropr iate age. According to the results of this study, this assessment would be overl y conservative. The inaccurate Nd values would be rejected by eliminating all samples whose 87Sr/86Sr value fell above the seawater curve, but nearly a third of th e viable values would also be reject ed. The results of this study do not eliminate Sr isotopes as an accurate test of the integrity of the Nd isot opic record, but they indicate that samples with accurate Nd values will also be rejected.

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97 9.4 Major Elements The major element data illustrate high vari ability within the extracted coatings, but there is very little correlation between the major element ratios and the accuracy of the Nd values. It is not clear that the major elem ent data actually reflect the ratios in a pure oxide coating. Brumsack (2005) analyzed major elements in black shales to determine if different suites of elements can give info rmation about the paleoenvironment during the deposition of these shales. In this study he discussed the effectiveness of some of these major elements as tools for identifying source locations for continental input into the oceans. Aluminum is unaffected by biologica l activity or diagenetic processes and is generally introduced by eolian or fluvial sources. The concentration of Al is generally high in clays, but low in seawater, with a short residence time in the oceans. He identified Al as the most effective elemen t for quantifying terrigenous detrital fractions. Titanium and K are also unaffected by biol ogical activity and predominantly sourced from the continents, thus they are also effective proxies for continental input (e.g. Dellwig et al., 2000; Wehausen and Brumsac k, 2002). Sodium is not very effective owing to the high Na concentration in seaw ater. The variability in the major element ratios is either an effect of the amount of influence from some clay and/or terrigenous material or variability in the amount of Fe and Mn in the coating. Since the extent of continental input varies between each of the locations used in this project, it would be expected that the ratios would also vary with location. There is undoubtedly some input of continental material associated with so me of the oxide coatings based on the Sr isotopic results and the large variability in ma jor element ratios (8-10A-B). Yet, this contamination apparently has little to no ef fect on the Nd isotopic composition of the

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98 coatings as there is no trend among samples that yielded fish teeth Nd values and those that did not. It is fairly difficult to determine what the major elements measured from these coatings indicate. It is clear that Na con centrations are highly affected by the Na from seawater. The Na/(Fe+Mn) ratios vary fr om nearly 400 to 0.08, suggesting that the samples need to be thoroughly washed in double distilled water prior to extraction. Some of the other elemental ra tios indicate concentrations of minor elements Al, Mg, and K that are higher than the concentrations of Mn plus Fe (e.g. Al/( Fe+Mn) ratios up to 10.0, K/(Fe+Mn) ratios up to 7.001, or a Mg/(Fe+M n ratios of up to 3.939). These high ratios are unlikely to represent pure extract ions of Fe-Mn oxide coatings. While the majority of the samples measured have low element to Fe plus Mn values more typical of values reported for Fe-Mn nodule standards (NOD-P and NOD-A), th ese high values are cause for concern. They sugge st that the extrac tion process is removing material other than what is expected, yet this additional co mponent does not seem be to effecting the Nd isotopic composition. 9.5 Sequential Extraction The results of the sequentia l extraction procedure support the conclusion that the Nd of Fe-Mn oxide coatings is not altered by the Nd isotopic value of the residual material. To test this conclusion further a mass balance calculation was performed using the Nd concentrations from each fraction of th e sequential extraction procedure. Table 92 shows the percent Nd contributed to the whole from each of the fractions; carbonate, Fe-Mn oxide coatings, and the residual sediment. The majority of the Nd in almost all the samples was extracted from the Fe-Mn oxi de fraction of the sediment. The one case

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99 where it was not was from sample 608, 213 where 54.34% of the Nd came from the residual fraction. This discrepa ncy may account for the incorrect Nd values obtained during the single extraction pr ocedure. These mass balan ce calculations show very decisively that the large of majority of Nd is coming from the coating fraction and if there were some contamination during the extractio n procedure from the residual fraction it would have a small impact on the Nd value. Table 9-2. Percent Nd cont ributed to the bulk sediment from the carbonate, Fe-Mn Oxide, and Residual Fraction Separa ted during the Sequential Extraction Procedure______________________ SampleCarbonate1Oxide1Residue1608 21-315.9229.7554.34 647 13-413.2960.4726.24 689 13-22.3192.964.73 689 15-43.6893.013.32 690 9-52.0295.332.65 690 10-50.5092.347.16 982 34-15.2991.453.26 982 47-16.6586.516.841determined using the starting weight of each sample and the weight after each extraction The fish teeth and Fe-Mn oxide extractions yielded the same Nd values for all 8 samples evaluated. These results are a bit di fferent from the single extraction experiment that yielded ~90% agreement between the coatings and the teeth. For the sequential extraction procedure the HH was stronger and th e sample was heated while being treated. Although the sequential extraction procedure was chemically more aggressive, the results indicated less influence by potential contamin ants. This is evident from both the Nd isotope values (figure 8-11) and the REE patte rns (figure 8-12A-D). In most cases the Nd values of the oxides and carbonate are much more radiogenic than the residual fractions. In one case (690, 10-5) it looks as if the carbonate fraction might have been affected by the residual fraction, as the Nd value fell between the teeth and the residual values. In two cases (608, 21-5 and 982, 47-1) the residual fraction fell within error of

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100 the coating and teeth values. This may indi cate that the coatings were not completely removed prior to the digestion of the resi due. Although it seems unlikely, the procedure for the sequential extraction isolate the Fe-Mn oxides more effective than the procedure developed for the single extraction, but furthe r tests of this idea are required. Interestingly the oxide coating fraction fr om the sequential extraction of sample 608, 21-5 (figure 8-11) yielded accurate Nd values when compared to fossil fish teeth and the residue was slightly less radiogenic, but with in error. In contrast the values from two single extraction samples were much more radi ogenic than contemporaneous teeth (figure 8-4). One cause of this discrepancy could be related to the REE concentrations inferred from the REE plots of the sequential extracti on which show that the sample from Site 608 had the highest concentrations for the residual fraction and the lowest concentrations for the coating (figure 8-13A-B). This is similar to the results of the REE measured from the single extraction samples, which again illustrated that the coating samples from site 608 had the lower concentrations than coatings from other sites (figure 8-8). The low concentration in the coatings at this sitemight allow the residual frac tion to have a greater influence on the isotopic signal, thus cr eating the discrepancy between the teeth and coatings. Although Site 608 is close to the Mid-At lantic Ridge, the sequential extraction results do not show any indication of radiogeni c Nd from hydrothermal contamination. In fact the residue from the one residue sample tested from Site 608 was slightly less radiogenic than other phases, which is consis tent with the terrigenous signature of the other residue samples. Given that it is so difficult to account for the offset observed in the single extraction samples from Site 608 and the agreement observed in the sequential

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101 leach from the site, one potential explanation is that there may have been an analytical problem in the preparation or measuremen t of the coating samples for the single extractions. There are only two samples from th is site and they were analyzed early on in the study before the correction between the TIMS and MC-ICP-MS had been thoroughly characterized; however, these samples were prepared and analyzed along with the single extraction samples from Site 647, and all of the coatings from that site fa ll within error of the teeth. It is intriguing, however, that th e coating values from Site 647 are consistently more radiogenic than the values for the te eth. Additional analyses from both of these sites would help determine whether there re ally is a component that introduces more radiogenic Nd into the oxi de coating extraction. The 87Sr/86Sr data support the idea that Sr isotop es from the coatings are altered in the direction of the radiogenic residual sedime nt fraction. In a number of samples the residual fraction is more radiogenic than the carbonate and the oxide coatings. The residual sediment seems to have altered th e oxide coating values for samples 689, 13-2 and 690, 9-5, as they are offset slightly towa rds the residual value. Even though the Sr isotopic values were altered for these samples, the Nd values appear to be unaffected. This supports the results obtained from the single extraction, which illustrated that Sr isotopic values were altered toward more radi ogenic values in a number of samples that showed agreement between fish teeth and oxide coating Nd values as well as samples that showed disagreement. The REE patterns of the sequential extractio n samples yield comparable results to the isotopic values. The Fe-Mn oxide R EE patterns for all 8 samples have a MREE bulge, representative of oxide coatings (figur e 8-12A-D and 8-13A-C). It does not seem

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102 that there was any influence from the resi dual fraction, which should flatten these patterns. The REE plots for the residua l fractions of samples 982, 47-1 and 647, 13-4 seems to be influenced by the coatings with enrichment in the MREEs, indicating that the oxide coatings were not completely remove d during the procedure. For most of the samples the carbonate fraction has a pattern simi lar to that of seawater, however for both 689 samples and 690, 10-5 the ca rbonate fractions have a larg e Eu anomaly (figure 8-12B and C). This anomaly mimics the REE pattern of the residual fractions for those samples, suggesting that the carbonate fraction has b een contaminated by the residual fraction in that the carbonate may be more of an open system than the Fe-Mn oxide coatings and incorporate some of the residual sediment si gnature. If this same contamination had affected the oxide coatings a similar anomal y would also be pres ent. Based on the isotopic data as well as the REE patterns, the Nd value of the extracted coatings were not influenced by the surrounding sediment when using this procedure. 9.6 An Alternate Explanation There is one other possible explanation for some of the results obtained in these studies. It may be possible th at phosphates present in the se diments are dissolved during the reduction of the Fe-Mn oxide coatings us ing the HH solution It is known that these pieces of bone debris and fossil fish scales effectively record deep water Nd isotopic values. In addition, phospha tes exhibit a MREE enrichment similar to the pattern characteristic of Fe-Mn oxide coatings. It has also been shown that Sr isotopes from phosphates do not record seawater values, but are altered toward pore waters values (Martin and Scher, 2004), thus explaining the va riable Sr isotopic results obtained in this study. This addition of phosphate material may be adding varying amounts of other

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103 major elements, causing the major element ratios measured to yield unexpected results. A very preliminary study was performed m easuring P(Fe+Mn) ratios on the carbonate and oxide fractions obtained dur ing the sequential extraction pr ocedure. These values of P(Fe+Mn) for just the oxide fraction ranged from 4.11 to 0.104, while this same ratio for the nodule standards are 0.005 and 0.020 for N od-P and Nod-A respectively. These results suggest that Phosphorous has been extracted during the HH extrac ting step of this procedure. The addition of this phosphate material does not seem to be a problem in terms of the extraction of Nd isotopes from Fe-Mn oxide coatings. Since both the oxide coatings and the phosphates are reliable archiv es for deep water Nd, the addition of the phosphates does nothing more than enhance the desired signal. Further analysis such as phosphorous measurements would be needed to refine this in terpretation.

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104 CHAPTER 10 CONCLUSIONS This study accomplished two di stinct goals. First, Nd isotopes preserved in fossil fish teeth were used to study circulation cond itions associated with two Late Cretaceous OAEs. Second, Fe-Mn oxide coatings ex tracted from marine sediments were demonstrated to be effective archives of deep sea Nd isotopes on Cenozoic to Cretaceous timescales. REE plots and Sr isotopes show that the Nd(t) values obtained from Late Cretaceous fossil fish teeth at Demerara Rise (Site 1258), in the equatorial Atlantic have not been altered by diagenesis. Therefore, th ese fish teeth affectiv ely record deep water Nd isotopic values. Before and after OAE2 and the MCE Nd(t) values at Demerara Rise average This value is distinct from values recorded in the North Atlantic, Pacific and Tethys oceans and suggests the basin surrounding Demerara Rise was relatively isolated and strongly influenced by local weathering inputs off the South American continent. There may have been intermed iate to deep water communications, however, between Blake Nose (Site 1050) and the No rth Pacific (Site 886) which both record relatively radiogenic Nd(t) values of -6 to -4. During OAE2 Nd(t) values increase by 8 Nd(t) units. This shift is larger than any shift documented throughout the worlds oc eans and it is tightly correlated to a 6o/oo excursion in 13Corg, indicating that changes in deep ocean circulation were involved in the development of OAE2. Previously hypothesi zed interpretations s uggested that deep ocean stagnation could have contributed to enhanced carbon burial; however, the Nd

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105 isotopic results argue for enhanced mixi ng and ventilation during OAE2 as values approached those of Blake Nose and the Pacific. Mechanisms that may have affected both 13Corg and Nd(t) at Demerara Rise include; 1) a change in sea level that ma y have allowed different water masses to overwhelm sills in the oceans causing increase mixing between water masses, as well as extraction of nutrients from coastal shel ves which would have caused increases in primary production, 2) changes to ocean wa ter chemistry caused by the eruption of the Caribbean LIP and increased ocean crust pr oduction, which would cause both increased nutrient loading into the oceans and, thus, in creased productivity, and the introduction of radiogenic Nd(t) values into the oceans that could have influenced waters at Demerara Rise, and 3) changes to upwelling along the co ast of the South American continent that brought nutrients to the surf ace waters which aided pr imary production as well as invigorating intermediate to deep ocean circ ulation. None of these mechanisms resolve all of the problems surrounding OAEs; however, the Nd results clearly illustrate that enhanced deep ocean circulation either played a role in the cause or responded to the anoxic events. The second half of the study was a systema tic evaluation of an extraction procedure to remove Fe-Mn oxide coatings from marine sediments for Nd isotopi c analysis. This is the first study to determine the validity of the Nd results from the extraction procedure by comparing them to the isotopic ratios obtained from contemporaneous fossil fish teeth. Results are as follows: 1. The extraction procedure is nearly 90% successful at extracting deep water Nd signals from oxide coatings from both the Southern Ocean and the North Atlantic on

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106 Cenozoic timescales, as well as from sample s from Late Cretaceous sediments from Demerara Rise in the North Atlantic. Although there was excellent agreement between the teeth and coatings at almost every si te, the oxide coatings from Site 608 were consistently distinct and more radiogenic than the teeth. All other tests (Sr isotopes, REE patterns, and elemental ratios ) suggest that any contamina tion at this site should be terrigenous and therefore less radiogenic. Additional tests wi ll be required to identify the source of the more radiogenic values, wh ich may be procedural or analytical. 2. Sr isotopes, REE, and major element ratios were all measured on the extracted oxide samples in order to deve lop a test of validity indepe ndent of fossil fish teeth. Neither REE patterns nor major element rati os can be used as stand-alone tests for validity. There was no conclusive trend in e ither of these tests th at would indicate a difference between extracted oxide coating Nd values that agreed with teeth and those that did not. REE patterns from all meas ured samples yielded patterns with MREE enrichment that is typical fo r Fe-Mn oxide coatings, while th e concentrations of the REE appear to be dependent on the sedimentation rate at a given location. Major element ratios varied considerably and there genera lly was no correlation to whether or not the oxide samples yielded Nd(t) values that agreed with contemporaneous fish teeth values. Sr isotopes are a very conser vative method for eliminating Nd(t) values that did not agree with the teeth values. In all cases samples that yielded Nd values distinct from the fish tooth values produced 87Sr/86Sr values did not fall on the seawater Sr curve; yet many of the samples that yielded agreem ent between the oxide and teeth Nd values also plotted off of the seawater Sr curve. By eliminating all samples th at fell off the curve about one third of the viable samples would also be discarded.

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107 3. A sequential extraction pr ocedure performed on 8 samp les from sites in both the Southern Ocean and the North Atlantic yielded results that were consistent with results obtained from the single extraction samples. Nd values and REE patterns from the oxide coatings were unaffected by the residual sedi ments, however in a few cases the carbonate fraction was contaminated. Sr isotopes from extracted coatings were susceptible to contamination from the residual sediments, producing Sr isotopic measurements that were altered towards more radiogenic values as demonstrated by the single extraction samples. Interestingly, the results from the sequential extraction procedure for samples from Site 608 yielded different results than the single extraction. There was no evidence of a source of more radiogenic material, whic h might suggest that the results obtained from the single extraction analys is could be the result of an analytical problem that needs to be evaluated. Results from this extraction study suggest that this procedure can be used as a method for extracting Nd values from Fe-Mn oxide coatings on marine sediments. A few fossil fish teeth samples should be measured from each site, however, to provide a check on the validity of this system at a specific site. Because the coatings yielded such consistent results compared to the fish teet h the extensive cleaning procedure on the teeth prior to analysis may be irrelevant, as it is designed to remove potential contamination due to the oxide coatings.

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119 Shipboard Scientific Party, 1999. Site 1090. In Gersonde, R., Hodell, D.A., Blum, P., et al., Proc. ODP, Init. Repts., 177 [Online]. Available from World Wide Web: < http://www-odp.tamu.edu/publications /177_IR/CHAP_01/Output/chap_01.htm >. [Accessed 2006-04-26] Sinton C.W. and Duncan R.A. (1997) Potent ial links between ocean plateau volcanism and global ocean anoxia at the Cenomanian-Turonian boundary. Economic Geology 92 234-246. Snow L.J., Duncan R.A., Bralower T.J. (2005) Trace element abundances in the Rock Canyon Anticline, Pueblo, Colorado, mari ne sedimentary section and their relationship to Caribbean plateau co nstruction and oxygen anoxic event 2. Paleoceanography 20 Spiess V. (1990) Cenozoic magnetostratigra phy of Leg 113 drill sites, Maud Rise, Weddell Sea, Antarctica, Proceedings of the Ocean Drilling Program, Scientific Results 113 261-315. Staudigel H., Doyle P., Zindler A. (1985) Sr and Nd isotope systematics in fish teeth. Earth and Planetary Science Letters 76 45-56. Stille P. and Fischer H. (1990) Secular vari ation in the isotopic composition of Nd in Tethys seawater. Geochim. Cosmochim. Acta 54 3139-3145. Tachikawa K., Jeandel C., RoyBarman M. (1999) A new approach to the Nd residence time in the ocean. Earth and Planetary Science Letters 170 433-446. Tachikawa K., Athias V., Jeandel C. (2003) Neodymium budget in the modern ocean and paleo-oceanographic implications. Jour. Geophys. Res. 108 3254, doi:10.1029/1999JC000285. Taylor S.R., and McLellen S.M. (1985) The Continental Crust: Its Composition and Evolution. Blackwell, Oxford 312 Thomas D. J., Brawlower T. J., Jones C. E. (2003) Neodymium isot opic reconstructions of the late Paleocene-early Eocene therrmohaline circulation. Earth and Planetary Science Letters 209 309-322. Thomas, D.J., Evidence of deep water producti on in the North Pacific Ocean during the early Cenozoic warm interval, Nature 430 65-68 van de Flierdt T., Frank M., Halliday A. N., Hein J. R., Hattendorf B., Gunther D., Kubik P. W. (2004) Deep and bottom water export from the Southern Ocean to the Pacific over the past 38 million years. Paleoceanography 19(1) Vance D. and Burton K. W. (1999) Neodymiu m isotopes in planktonic foraminifera: A record of the response of continental w eathering and ocean circulation rates to climate change. Earth Planet. Sci. Lett. 173 365-379.

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121 BIOGRAPHICAL SKETCH Susanna Whitman Blair was named after her mothers favorite poet, Walt Whitman. Her primary education, elementa ry through high-school, was completed in Baltimore, Maryland, a place that still feels like home to her. During a summer camp, she attended in high-school, she first became in terested in geology and knew that when it was time to go to college she at the very least wanted a school that had a good geology department. She found this at Colgate Univer sity in Hamilton, NY, and began her studies there in the fall of 1999. During this time she did research on the vol canic history of the Galapagos Islands and was fortunate enough to tr avel there to do some field work. This exposure to scientific research was the e xperience she needed to know that graduate studies were what she wanted to do next. She completed her degree in the spring of 2003 with a Bachelor of Arts with a focus in geology, knowing that she would be attending the University of Florida in the fall to begin work on her masters degree. At UF her research focused on Nd isotopes as a proxy for ocean circulation. Susanna plans on graduating in the summer of 2006 and shortl y will be working for an environmental consulting firm in Jacksonville.


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Title: ND Isotopes: Investigation of Cretaceous Ocean Anoxic Event 2 and a Systematic Study of Fe-Mn Oxide Coatings
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Copyright Date: 2008

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Material Information

Title: ND Isotopes: Investigation of Cretaceous Ocean Anoxic Event 2 and a Systematic Study of Fe-Mn Oxide Coatings
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

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Holding Location: University of Florida
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ND ISOTOPES:
INVESTIGATION OF CRETACEOUS OCEAN ANOXIC EVENT 2
AND A SYSTEMATIC STUDY OF FE-MN OXIDE COATINGS
















By

SUSANNA WHITMAN BLAIR


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2006



























Copyright 2006
by
Susanna Whitman Blair



























This document is dedicated to Dr. Mary K. Blair and Dr. Blair Plimpton.















ACKNOWLEDGMENTS

I would first like to sincerely thank Dr. Ellen Martin for her continued help and

guidance on this project. Though there were a number of challenges and setbacks, she

was always persistent and positive about the progress. She is not only a wonderful

advisor and mentor but a dear friend and confidant. I will undoubtedly miss her. Thanks

go also to my committee members Dr. Paul Mueller and Dr. Philip Neuhoff for their

advice and review of this thesis.

I am also very grateful for the financial support that was provided by the NSF SGR

grant awarded to Dr. Ellen Martin.

Special acknowledgements go to Dr. George Kamenov for his patience and

continuous help. This project would not have been completed without his guidance,

suggestions, laboratory help, and assistance with analysis equipment. He is a true asset to

this department and I was very lucky to have worked with him. Thanks go also to Dr.

Ann Heatherington for her assistance with the TIMS. Thanks also go to Ken MacLeod

for his help with the OAE portion of this project.

An appreciative thank you goes to Dr. Howard Scher for his guidance and help in

the laboratory at a very early stage. He was definitely the force behind the start of this

project and a number of the early analysis. I would also like to thank Derrrick Newkirk

and the many others who have helped me in the laboratory.

Finally, I would like to thank my family and friends. Thanks go to Mary Blair for

her unfaltering love and support. She is my dearest friend. Thanks go to Blair Plimpton









for being the first geologist in the family. Thanks go to David Sutton for his love and

never- ending encouragement. Thanks go to my many wonderful friends in the

Department of Geological Science at UF, especially to Jillian Hinds, Gillian Rosen,

Warren Grice, Derrick Newkirk, Jane Gustavson, and Kelly McGowan for their

friendship and laughter. Thanks go to Dr. Karen Harpp for her encouragement to

continue on to graduate school. And last but not least thanks go to my many wonderful

friends from Colgate University and from Baltimore, especially Miranda Clark for

reading the following.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S ................................................................................................. iv

L IST O F T A B L E S ........................ .... .... ........................ .. .. .. .... .............. viii

LIST OF FIGURES ......... ......................... ...... ........ ............ ix

ABSTRACT ........ .............. ............. ...... .......... .......... xi

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 GENERAL BACKGROUND ........................................................................6

2.1 Isotope System atics ............................................................6
2 .1.1 N eodym ium ....................................................... 6
2.1.2 Strontium ...............................................................8
2 .1 .3 C arb o n ....................................................... 9
2.2 General Ocean Circulation ................. .................................10
2.3 A archives of N d isotopes ........................................................... .................. .. 11
2.4 D description of Sam ple Sites................................... ................... 16
2 .4 .1 D SD P Site 608 ........................................................ 16
2 .4 .2 O D P S ite 6 4 7 ........................................................................................ 17
2 .4 .3 O D P S ite 6 8 9 ........................................................................................ 18
2 .4 .4 O D P site 6 9 0 ......................................................................................... 18
2 .4 .5 O D P S ite 8 8 6 ......................................................................... 19
2 .4 .6 O D P S ite 9 8 2 ........................................................................................ 19
2 .4 .7 O D P S ite 10 5 0 ...................................................................................... 2 0
2.4.8 O D P Site 1090 ............................................ ....... .............................20
2.4.9 ODP Sites 1258, 1259, 1260 .......................................... 20

3 M E T H O D S ........................................................................................................... 2 3

3.1 Sample Preparation......................................... 23
3.1.1 Fossil Fish Teeth Preparation .............................................. ............... 23
3.1.2 Fe-M n Oxide Coating Preparation ........................................ ............. 23
3.2 Sr and N d Colum n Chem istry.............................................. ......................... 24
3.3 N d A analysis ....................................... ............ .........................................25
3.4 Major Element and REE Analyses from Fe-Mn oxide coatings ..........................28









3.5 Sequential Extraction Procedure......................... ..... .. ..................29
3.6 Analysis of Nd and Sr isotopes, and Rare Earth Elements from Sequential
E x tra c tio n s ............................................................................................................. 3 1
3.7 Sr A nalysis................................................... 32

4 BACKGROUND FOR THE CRETACEOUS STUDY........................ ..........34

4.1 General Climate Change and Tectonic Orientations ........................................34
4.2 Cretaceous O cean Circulation ........................................ ......................... 35
4 .3 O cean A noxic E v ents ........................................ ............................................36

5 RESULTS FROM THE CRETACEOUS OAE STUDY .....................................43

6 DISCUSSION OF CRETACEOUS OAE STUDY ......................... .....................50

7 BACKGROUND ON EXTRACTION EXPERIMENTS .......................................60

8 RESULTS OF THE FE-MN OXIDE COATING EXTRACTION PROCEDURE
A N D V A L ID IT Y TE ST S ........................................................... ..........................62

8.1 Variations on the Extraction Procedure..... .......... ..................................... 62
8.2 R results from Southern O cean Sites ........................................... .....................65
8.3 Results from N orth Atlantic Sites................................ ................................. 69
8.4 Results from Cretaceous Sam ples ............................................. ............... 72
8.5 T ests of V validity .......................................................................... ......................73
8 .5 .1 R E E P lots.....................................................74
8.5.2 Strontium Isotopes .......................... ..... ............... 78
8.5.3 M ajor E lem ent R atios.............................................. ............... ... 80
8.5.4 Sequential Extraction Procedure Results ......... .................................... 84

9 DISCUSSION OF EXTRACTION RESULTS FROM THE SOUTHERN OCEAN;
NORTH ATLANTIC; AND CRETACEOUS AGE SAMPLES ............................91

9.1 Possible Lithologic Effects on the Extraction Procedure ...................................91
9.2 REE Patterns of Fe-Mn oxide coatings ..... ...............................93
9 .3 Sr Isotop es .........................................................................9 5
9.4 M major Elem ents ................................................... ............ .... ..... 97
9 .5 S equ ential E xtraction ......................................... .............................................9 8
9.6 An Alternate Explanation ............................................................................ 102

10 C O N C L U SIO N S ................... ................................ ...... ........ ...... ........... 104

L IST O F R E FE R E N C E S ........................................................................ ................... 108

BIOGRAPHICAL SKETCH ............................................................. ............... 121
















LIST OF TABLES


Table page
2-1 Nd Isotopic Data for Modem Seawater to Show the Variation in Values of
M aj or W after M asses ............... ................. ..................... ...... .... 7

5-1 Site 12 58 m cd and 13C ...................................................................... ......44

5-2 Sr and Nd Values from Cretaceous Samples from ODP Sites 886, 1050, 1258,
1259, 1260 ........................................................................ ...........48

6-1 REE Values from Fossil Fish Teeth Samples Before, During and After OAE2......52

8-1 Nd Isotopic Values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from
Southern Ocean ODP Sites 689, 690, and 1090......... ...................................... 68

8-2 Nd Isotopic Values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from
North Atlantic DSDP and ODP Sites 608, 647, and 982 ......................................72

8-3 Nd Istopes from Fossil Fish Teeth and Fe-Mn Oxide Coatings from Sites 1258
and 1050 ............................................................................73

8-4 REE Values from Fe-M n Oxide Coatings..................................... ............... 77

8-5 87Sr/86Sr Values from Extracted Material and Foraminifera from Samples from
OD P Sites 689, 690, 982, and 1090 .............................................. ............... 80

8-6 Major Element Rations from Site 608, 647, 690, 1090, and 1258.........................82

8-7 143/144Nd values for Fossil Fish Teeth, Carbonate, Fe-Mn Oxide Coatings, and
Residual Fractions from the Sequential Extraction Samples .................................86

8-8 87Sr/86Sr Values for Seawater, Carbonate, Fe-Mn Oxide Coatings, and
Residual Fractions from the Sequential Extraction Samples .................................86

8-9 REE Values from Sites 608, 647, 689, 690, and 982 from Three Sediment
Fractions ................ .......... .......................... ...........................90

9-2 Percent Nd Contributed to the Bulk Sediment from the Carbonate, Fe-Mn
Oxide, and Residual Fraction Separated during the Sequential Extraction
Procedure ............... ........... .......................... ...........................99















LIST OF FIGURES


Figure pge
2-1 Variation of the 7Sr/86Sr ratio of seawater through the Cenozoic............................9

2-2 G general O cean Circulation m odel ................................................. ....... ........ 11

2-3 SNd from sites in the Atlantic sector of the Southern Ocean spanning 20 kyr to
present, plotted with 6180 values from the GRIP ice core and sea ice variations
from the W western N orth Atlantic. ................................ ................................. 15

2-4 M oder plate reconstruction.................................... ..................................... 16

2-5 Stratigraphic section of Cretaceous sequence for Site 1258 on Demerara Rise
showing the three major lithostratigraphic intervals recovered: ........................21

3-1 The difference between the SNd(O) values of 11 samples measured on the TIMS
and the NU -M C-ICP-M S. ................................. ....................................... 27

4-1 Tectonic plate reconstruction at 90Ma showing the open connection between the
A tlantic and Pacific O ceans ............................................................................... 40

4-2 The seawater Sr isotope curve with 3 OAEs that coincide with perturbations in
th e S r isoto p ic v alu es........... ..... ......................................................... .... .... .. ....4 1

4-3 Relative ocean crust and plateau production over time. .......................................41

4-4 Eustatic sea level curve of the last 200 M a. ........................................ ................42

5-1 613C and TOC % from ODP Site 1258 from 410-490 mcd. ..................................43

5-2 SNd(t) and 613C values from Site 1258 from 370 to 490 mcd. ..............................45

5-3 High resolution 613Corg with the SNd(t) values spanning OAE2 (420-428 mcd)
from ODP Site 1258.................... .. ..................... .......... 46

5-4 SNd(t) values from Site 886 in the Pacific Ocean, Sites 1259, 1258, and 1260 from
Demerara Rise, and Site 1050 from Blake Nose spanning 65-103 Ma ..................47

6-1 7Sr/86Sr seawater curve from 85-100 Ma along with the Sr isotopic values from
fossil fish debris collected from Site 1258. ...................................... ............. 51









5-3 REE plots of modern seawater compared to samples from before, during, and
after O A E 2. ..............................................................................52

8-1 The difference of SNd between fossil fish and Fe-Mn oxide coatings from
samples of < 63 |tm, 63-125 |tm and >125 |tm size fractions. S. .........................63

8-2 Difference of ENd from obtained from fossil fish teeth and samples treated for 4,
2, and 1 hour extraction periods. ........................................................................65

8-3 SNd(o) values from fossil fish teeth and Fe-Mn oxide coatings from the Southern
O cean Sites ............................................. ............................ 66

8-4 SNd(o) values from fossil fish teeth and Fe-Mn oxide coatings from DSDP Site
608 and ODP Site 647 from 5.5 to 9 and from 30 to 31 Ma..................................70

8-5 SNd(o) values from fossil fish teeth and Fe-Mn oxide coatings from ODP Site 982
from 9 to 15 M a ............................. ......... ...... ................... ......... 71

8-6 SNd(t) values from fossil fish teeth and Fe-Mn oxide coatings from ODP Sites
1258 and 1090 from 77 to 102 M a. ........................................ ....................... 73

8-7 REE plot of four samples from ODP Site 690 .....................................................74

8-8 REE plot of the average values from extracted coatings from the North Atlantic
Sites 608, 647, and 982, the Cretaceous (Sites 1258 and 1050), and the Southern
O cean Sites 1090, 690, and 689... ........................ ..............................................76

8-9 Seawater Sr curve over the past 50 Ma plotted with 87Sr/86Sr values from
extracted Fe-M n oxide coatings. ........................................ ......................... 79

8-10 Ti/(Fe+Mn) ratios of samples vs. the difference between SNd values of the fossil
fish teeth and the coatings from Sites 608, 647, 689, 690, 982, 1090, and the
Cretaceous samples from Sites 1050 and 1258 ........................................... ........... 82

8-11 SNd(o) and 87Sr/86Sr values from 8 sequential extraction samples ............................85

8-12 REE patterns from 8 sequential extractions. ...................................................88

8-13 REE patterns for 3 sediment fractions for sequential extractions. .......................90

9-1 Weight percent opal, carbonate, and terrigenous material from Site 1090 from
19.2 to 25.1 Ma plotted against the difference between SNd values from fossil
fish teeth and Fe-M n oxide coatings. ............................................ ............... 92

9.2 Average sedimentation rate versus Nd concentration for Sites 608,647, 982, 689,
690, 1090, and 1258. .......................... ........... ...... ...... ...... ...... 95
















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

ND ISOTOPES:
INVESTIGATION OF CRETACEOUS OCEAN ANOXIC EVENT 2 AND
A SYSTEMATIC STUDY OF FE-MN OXIDE COATINGS
By

Susanna Whitman Blair

August 2006

Chair: Paul Mueller
Major Department: Geological Sciences

Nd isotopes in seawater are quasi-conservative water mass tracers and, therefore, can be

used to reconstruct deep sea circulation through time, allowing scientists to further examine the

link between ocean circulation and climate. This two-part study first explores circulation patterns

in the North Atlantic during Late Cretaceous Ocean Anoxic Events (OAEs) using fossil fish teeth

as an archive for Nd isotopes. Second, iron-manganese (Fe-Mn) oxide coatings on marine

sediments are systematically tested as a potential new archive on Cenozoic timescales.

A high resolution Nd isotopic record was constructed for Site 1258 on Demerara Rise

spanning OAE2 and the Mid-Cenomanian Event (MCE). Low resolution Nd isotopic records

were also compiled from fossil fish teeth collected from ODP Sites 1259 and 1260 also on

Demerara Rise, as well as Site 1050 (Blake Nose), and Site 886 (Central North Pacific). Data

indicate that Nd isotopes are unaffected by diagenetic alteration. Average SNd values of -15

before and after the OAEs at Site 1258 suggest that Demerara Rise was highly influenced by

weathering off the South American continent. During OAE2 a very large, rapid increase of 8 SNd

units coincides with the increase in total organic carbon and the -6%/oo positive excursion in










613Corg. Competing causal theories for OAE2 attribute this anoxic event and the major shift in the

global carbon budget to enhanced surface productivity or stagnation of the deep ocean. The

rapid, positive increase in SNd at Site 1258 approaches values observed at Blake Nose (subtropical

North Atlantic) and in the Pacific around this time (SNd = -4 to -6), indicate enhanced, rather than

reduced, deep water circulation. This enhanced circulation may have been associated with

increased rates of upwelling, contributing to surface productivity and increased carbon burial.

Fossil fish teeth are effective archives for Nd isotopes, yet they are not always present in

sediment samples and are laborious to collect. Fe-Mn oxide coatings are present throughout time

and space, can be accurately dated, and have proven to be reliable archives on Pleistocene time

scales. Other studies have not had a method to test the accuracy of the oxide coating values. In

this study SNd results from these coatings were compared to fossil fish teeth values for samples as

old as the Cretaceous. For -90% of the samples from the Miocene to Eocene in the Southern

Ocean (Sites 689, 690, and 1090) and North Atlantic (Sites 608, 647, and 982), as well as

Cretaceous samples from Site 1258 the coatings and fish teeth yielded the same SNd values.

A number of independent tests evaluated the selectivity and efficiency of the extraction

procedure, including Sr isotopic analyses, REE patterns, and major element ratios. Sr isotopes

were identified as a very conservative test. A sequential extraction procedure was also tested to

determine the isotopic signature and REE patterns of various sediment fractions. It was

concluded that terrigenous material in the sediments may affect the Sr isotopes, but not the SNd

values. Although these results indicate that Fe-Mn oxide coatings are a robust archive of deep

sea Nd isotopes, it is necessary to test a few samples from each site against fossil fish teeh SNd

values. Preliminary results indicated that some of the Nd isotopic signal may also be coming

from phosphates within the sediment. It can also be concluded that the rigorous cleaning

procedure of fossil fish teeth prior to analysis is not necessary.














CHAPTER 1
INTRODUCTION

Throughout earth's history a number of climatic events have been linked to

dramatic changes in ocean circulation. Examples include the correlation between the

onset of the Antarctic Circumpolar Current, the thermal isolation of Antarctica, and the

development of large ice sheets on Antarctica (Kennet, 1977; Scher and Martin, 2006).

The correlation between the closure of the Central American Seaway (CAS) and the

onset of modern thermohaline circulation, as well as Northern Hemisphere glaciation

represents another example. By identifying changes to ocean circulation in the past

scientists hope to better understand forcing mechanisms, rates of change, and possible

effects of climate change. Global warming is quickly becoming one of the most

important issues of our time. The melting of polar ice caps and permafrost, and the

intense weather conditions across the globe have many concerned. By identifying major

climatic changes in the past and understanding their forcing mechanisms we may be

better prepared for future climate changes.

A conservative tracer for ocean circulation is required to evaluate to the role ocean

circulation plays in the development of global climate on geologic timescales.

Neodymium is one of the few possible tracers for this property. Neodymium has been

used in a number of studies to evaluate changes in deep water circulation over a range of

time scales (e.g. Ling et al., 1997; O'Nions et al., 1998; Winter et al., 1997; Frank

anNions, 1998; Frank et al., 1999; Vance and Burton, 1999; Frank et al., 2003; Thomas et

al., 2003; Martin and Scher, 2004; Piotrowski et al., 2005; Scher and Martin, 2006).









Different water masses can have distinct Nd isotopic values (Piepgras and Wasserburg,

1982 and 1987; Piepgras and Jacobsen, 1988; Bertram and Elderfield, 1993; Jeandel,

1993; Shimizu et al., 1994; Jeandel et al., 1998) because the residence time of Nd in the

world's oceans is shorter than the mixing time of the ocean itself (Broecker and Peng,

1982; Elderfield and Greaves, 1982; Piepgras and Wasserburg, 1985; Jeandel et al., 1995;

Tachikawa et al., 1999) and because the Nd isotopic signature is dominated by the local

geology of the source regions. Unlike other potential tracers, such as 613C or Cd/Ca, Nd

isotopes are not fractionated by biological processes or temperature. Tracking deep water

Nd isotopes through time and space can lead to greater understanding of past deep ocean

circulation patterns. In order to utilize this tool, an effective archive has to be identified

that preserves the Nd isotope values over time. Some of the archives that have been used

in paleoceanographic studies include ferromanganese (Fe-Mn) crusts and nodules, fossil

fish teeth, and authigenic Fe-Mn oxide coatings (e.g. Albarede and Goldstein, 1992;

Frank and O'Nions, 1998 and 1999; Martin and Haley, 2000; Frank et al., 2003; Thomas

et al., 2003; Martin and Scher, 2004; Piotrowski et al., 2004; Scher and Martin, 2006).

This thesis presents two unique studies; one applies Nd isotopes from fossil fish

teeth to study the relationship between ocean circulation and the development of Ocean

Anoxic Events (OAEs) in the Cretaceous, and the second evaluates the potential of Fe-

Mn oxide coatings on marine sediments as a possible archive for Nd isotopes on

Cenozoic timescales.

The Cretaceous was a time of drastic changes in the world's oceans. One extreme

event during this time was Ocean Anoxic Event 2 (OAE2), which is associated with large

scale changes to the ocean's carbon budget (e.g. Schlanger and Jenkyns, 1976; Jenkyns,









1980, Arthur et al., 1988; Kuypers et al., 2002). This net burial of organic carbon around

the Cenomanian-Turonian boundary occurred during the peak of the Cretaceous

greenhouse climate interval. Widespread evidence for this event is present in all the

world's oceans in the form of laminated, organic-rich silt and claystones virtually devoid

of benthic fossils, indicating anoxic bottom waters over much of the seafloor. OAE2 is a

global event and coincides with shifts in ocean chemistry, extinction of planktonic

nannofossils (e.g. Leckie et al., 2002), the emplacement of the Caribbean large igneous

province (LIP) (e.g. Kerr, 1998), and a highstand of sea level (e.g. Jenkyns, 1991); yet the

ultimate cause of anoxia during this interval is still debated. The debate centers around

whether the anoxic conditions that lead to the OAE2 were created by: 1) increased decay

of organic carbon in response to enhanced surface productivity (largely a surface

phenomenon), or 2) reduced ventilation and stagnation (largely a deep water

phenomenon). Nd isotopes, which have been shown to effectively track ocean

circulation, offer a unique opportunity to evaluate whether or not OAE2 was associated

with changes in deep ocean circulation.

Nd isotopes from fossil fish teeth and debris were analyzed and compared to carbon

isotopic data from OAE2 on the Demarara Rise (ODP Leg 207, Sites 1258, 1259, and

1260) in order to distinguish between proposed causal mechanisms. Nd isotopic data

from Site 886 in the central north Pacific Ocean and Site 1050 from the subtropical north

Atlantic (Blake Nose, Leg 171B) also helped constrain possible interpretations. Results

from this study illustrate that there is a very dramatic response to OAE2 in the Nd

isotopic record.









Although fossil fish teeth have proven effective for the generation of high

resolution Nd isotope records on Cenozoic time scales (Martin and Haley, 2000; Martin

and Scher, 2003; Thomas et al., 2003; Thomas, 2004) and the temporal resolution of Nd

records from fossil fish teeth represents an enormous improvement relative to Fe-Mn

crusts, the resolution is still not as high as traditional paleoceanographic proxies because

the yield of teeth is highly variable. Moreover the method used to extract Nd from fossil

fish teeth is very labor intensive. This project explores an alternative archive for creating

these records. The dispersed, authigenic, Fe-Mn oxide coatings, common on marine

sediments, have high concentrations of Nd and have been used to generate high

resolution Nd isotope records on glacial-interglacial time scales (Rutberg et al., 2000;

Bayon et al., 2002; Piotrowski et al., 2004). This project evaluates the preservation of

initial Nd isotopes from Fe-Mn oxide coatings over Cenozoic time scales and seeks to

identify a simple test of the integrity of the preserved signal.A reductive extraction

procedure developed by Rutberg et al. (2000) and Bayon et al. (2002) to remove Fe-Mn

oxide coatings was modified and applied to selected sediment samples of Miocene to

Eocene age from Ocean Drilling Program (ODP) Sites 689, 690, and 1090 in the

Southern Ocean and from DSDP (Deep Sea Drilling Program) and ODP Sites 608, 647,

and 982 in the North Atlantic. To test the validity of the isotopic values obtained, the

coating values have been compared with Nd isotopic values of contemporaneous fossil

fish teeth. It is assumed throughout the study that the value obtained from the fossil fish

teeth accurately reflects the Nd isotopic composition of the seawater at the time of

deposition (Staudigel et al., 1985; Elderfiled and Pagette, 1986; Martin and Haley, 2000;

Martin and Scher, 2004). This method of verifying the integrity of the signal preserved









in Fe-Mn oxide coatings is unique to this study. The sediment size fraction, extraction

time, and extraction agents have been altered from the original Bayon procedure (Bayon

et al., 2002) to obtain Nd isotopic values that match those of the fish teeth. The main

concern with this extraction technique is possible contamination from the detrital

material, which would undoubtedly alter the isotopic value. Less labor-intensive

methods of verifying the integrity of the signal extracted from the oxide coatings have

been tested. These tests were specifically designed to detect detrital contamination. The

tests include studies of major element ratios, rare earth element (REE) patterns, and Sr

isotopes. During the study a sequential extraction procedure was also applied to several

samples to determine the Nd isotopic values of several distinct components: the fish

teeth, carbonate, Fe-Mn oxide, and residual fractions of the sediment. The development

of a reliable procedure for effectively extracting Fe-Mn oxide coatings from marine

sediments would allow for a more continuous sampling of the ocean sediments and the

development of a more complete reconstruction of ocean circulation through time.














CHAPTER 2
GENERAL BACKGROUND

2.1 Isotope Systematics

2.1.1 Neodymium

Neodymium is a lanthanide series element that has seven isotopes. 143Nd is a

radiogenic daughter product of 147Sm produced by alpha decay with a half-life of

approximately 1.06x10-11 years. The 143Nd/144Nd ratio is measured and commonly

reported as ENd. This notation allows small, but significant, variations in the isotopic ratio

to be reported in whole numbers relative to a bulk Earth value (DePaolo and Wasserburg,

1976) and is determine by the equation below.

ENd(O) [(143Nd/14Nd)sampe /(143Nd/144Nd)CHUR -1] x 104

Where CHUR (Chondritic Uniform Reservoir) is equivalent to the bulk Earth

143Nd/144Nd ratio or -0.512638 (DePaolo and Wasserburg, 1976). Continental material

has ENd values of 0 to -50 while mid-ocean ridge basalts (MORB) have values of 0 to +

12 (Piepgras and Wasserburg, 1980).

Neodymium is a direct weathering product from the continents and generally

reflects the relative ages and type of the weathered bedrock. The residence time of Nd in

the world's modern oceans is -1000 years (Elderfield and Greaves, 1982; Piepgras and

Wasserburg, 1985; Jeandel et al., 1995; Tachikawa et al., 1999 and 2003), which is

shorter than the total mixing time of the ocean (-1500 years; Broecker and Peng, 1982).

The various ages and types of the weathered material in deep water source regions and









the relatively short mixing time of Nd in the oceans indicate that Nd isotopes can be used

to track deep water masses.

Although Nd isotopes in seawater covary with other conservative tracers, such as

salinity and silica (Rutberg et al., 2000; Goldstein and Hemming, 2003), Nd is not a

perfect conservative tracer for water masses because the signal of ocean water masses can

be altered by weathering inputs within a basin. Frank et al. (2003) termed Nd isotopes

"quasi-conservative" water mass tracers due to this possible modification. One example

of this effect is that Pacific waters have an ENd value of -4 derived from relatively young

Pacific Rim volcanic rocks despite the fact that most of the water masses flowing into the

basin have ENd values < -8. However, variations in ocean circulation can still be detected

above this weathering signal (Piepgras and Jacobsen, 1988) (table 2-1). In comparison

the North Atlantic, which is surrounded by old Pre-Cambrian cratons, has ENd values of

-13 to -14. Finally, the Indian Ocean has ENd values of -8, which reflects the

weathering input from surrounding landmasses, as well as a mixture of Atlantic and

Pacific values (Piepgras and Wasserburg, 1979).

Table 2-1. Nd isotopic data for modem seawater to show the variation in values of major
water masses
Water mass Modern SNd
AAIW (Antarctic Intermediate Water) -7 to -8
AABW (Antarctic Bottom Water) -9 1
PDW (Pacific Deep Water) -4 2
NAIW (North Atlantic Intermediate Water) -13 3
NADW (North Atlantic Deep Water) -13.5 3
1.Jeandel, 1993; 2. Piepgras and Jacobsen, 1988; 3. Piepgras and Wasserberg, 1987

Neodymium is primarily sourced from continental sources including atmospheric dust,

volcanic ash, resuspended detrital sediments, dissolved riverine input and river-borne

particulates (Goldstein and Jacobsen, 1988; Bertram and Elderfield, 1993; Albarede et









al., 1997; Tachikawa et al., 1999 and 2003). Nd emitted at hydrothermal sources is

thought to be scavenged almost immediately and therefore does not have an effect on

waters beyond the immediate source area (Michard, 1983; German et al., 1990). Nd ions

are relatively insoluble and very particle reactive, thus the concentration of Nd in

seawater is fairly low, -4 pg/g in the deep water. Nd is quickly scavenged by detritus,

fecal pellets and oxide coatings in the water column and deposited on the ocean floor.

2.1.2 Strontium

Strontium isotopes have been used in this study as a chronostratigraphic tool as

well as an independent test of the validity of the Nd isotopic value of the extracted Fe-Mn

oxide fraction. The Sr isotopic value of the ocean is a function of a number of inputs;

crustal weathering by riverine systems, which have radiogenic 87Sr/86Sr values (-0.7119),

mantle derived material from hydrothermal venting with non-radiogenic values of

-0.7035 (Palmer and Edmond, 1989), and pore water diffusion which introduces Sr with

the isotopic ratio of old marine carbonates (Hess et al., 1986; Hodell et al., 1990).

Strontium has a residence time in the oceans on the order of several million years

(Hodell et al., 1994), which creates a homogeneous ocean with respect to 7Sr/86Sr at any

one time in earth's history. The major sink for Sr is carbonate precipitation, because the

Sr2+ ion can easily replace Ca2+. Extensive work has been done to document the changes

in Sr over the past 50 Ma (figure 2-1). Strontium isotopes illustrate a general increasing

trend throughout the Cenozoic making them a fairly effective tool for chemostratigraphy.










0.70921

0.709
0.709


0.7088

0.7086

c 0.7084
-- -- -- --- ---
0.7082


0.708


0.7078 ----------

0.7076
0 10 20 30 40 50
Age (Ma)

Figure 2-1. Variation of the 87Sr/86Sr ratio of seawater through the Cenozoic. Data from
Hodell and Woodruff, 1994; Farrel, 1995; Mead and Hodell, 1995; Martin et
al., 1999.

2.1.3 Carbon

Carbon isotopes extracted from ocean sediments are used to track carbon transfers

into and within oceanic reservoirs. Carbon moves through these reservoirs as organic

carbon, which consists of both living and dead matter, and inorganic carbon, which is

primarily dissolved ions, but can also include atmospheric CO2. Marine foraminifera

have preserved inorganic carbon throughout the geologic record and are commonly used

as an archive for carbon isotopes. Carbon isotopes are fractionated during photosynthesis

because living organisms preferentially incorporate 12C instead of 13C into their tissue.

This fractionation shifts the 613C value of organic matter toward more negative, 12C

enriched values, relative to that of inorganic carbon (Goodney et al., 1980), leaving the

oceans enriched in 13C. During times of increased primary productivity in the oceans the









613Corg of foraminifera and bulk organic matter shifts toward more positive values. In this

study carbon isotopic ratios in bulk organic matter are interpreted to represent the global

signal of net organic burial and provide an independent record of the position of OAE2.

Carbon isotopes can also be used as a tracer of water mass age. In young deep

waters that have recently been at the surface, such as modem North Atlantic Deep Water

(NADW), 613C is more positive, reflecting the recent ventilation of surface waters

influenced by extensive photosynthesis. As this water circulates and becomes older 12C

is progressively returned to the water through organic decay and the 613C becomes more

negative. Carbon is considered a non-conservative water mass tracer because it can be

altered by changes in productivity. It provides information about how long the deep water

has been away from the surface and the extent of surface productivity, but it does not

record information about the source region of the deep water.

2.2 General Ocean Circulation

The modern ocean circulation model is relatively well constrained and is controlled

by the sinking of cold, saline water in the high latitudes. Highly simplified, the cycle

begins as NADW sinks in the North Atlantic, due to its cold temperature and high

salinity, both of which make this water relatively dense. This water mass makes its way

to the Southern Atlantic where it mixes with Antarctic Bottom Water (AABW), which is

formed around Antarctica, because of the cold temperatures and high salinities associated

with sea ice formation. These water masses combine and continue east in a circumpolar

current, flow into the Indian Ocean and into the Pacific, and eventually return through the

Drake Passage and the Indonesian Seaway as intermediate and surface waters. This

process is referred to as the global conveyor (Broecker and Peng, 1982) (Figure 2-2).









Cooling and sinking of warm NADW keeps Europe relatively warm for its latitude. The

rate of conveyor cycling is approximately 103 years (Broecker and Peng, 1982).















IsrM M19 LEMM 5MINE RTW CIRCUMPOLAR CU

Figure 2-2- General Ocean Circulation model, adapted from Broecker and Peng, 1982.
(www.metoffice.gov.uk)

This ocean circulation pattern has evolved through geologic time. Some of the

factors that control the deep ocean circulation pattern include openings and closings of

oceanic gateways, as well as changes in the thermal gradient and conditions in source

regions. The Late Cretaceous circulation, specifically, was very different from today's;

at that time the North Atlantic had recently opened, creating isolated basins between sills

and fractures in the ocean floor (Bonatti et al., 1994; Jones et al., 1995; Handoh et al.,

1999).

2.3 Archives of Nd isotopes

To determine the Nd value of seawater in the past a physical storehouse or archive

has to be identified that incorporates Nd from the seawater into its structure and

maintains its integrity through burial and diagenesis. In order to reconstruct ENd changes

this archive must be found throughout space and time, and must be datable. Identified









archives include biogenic carbonate, ferromanganese (Fe-Mn) oxide crusts and nodules,

phosphates (particularly fossil fish teeth), and Fe-Mn oxide coatings.

Biogenic carbonates have been used as an archive for many other chemical proxies

(ex. strontium, carbon, and oxygen isotopes); however, the concentration of Nd in

carbonates is very low, on the order of a few ppm, because Nd3+ is the wrong size and

charge for the carbonate structure (Palmer and Elderfield, 1985). Early studies that

attempted to extract Nd from planktonic foraminifera found that 90% of the Nd was in

the Fe-Mn coating with only 10% in the carbonate (Palmer and Elderfield, 1985). Nd

values obtained from un-cleaned foraminifera yielded 143Nd/144Nd values similar to those

of Fe-Mn crusts from a similar location and time period (Palmer and Elderfield, 1985).

Other studies have suggested that after intensive redox cleaning the Nd isotopic value of

planktonic foraminifera records the surface water value (Vance and Burton, 1999). It is,

however, unclear if any cleaning can remove all of the coating and produce isotopic

values purely from the carbonate (Pomies, 2000). Although foraminifera are abundant

throughout the world's oceans it is unclear whether they can be used as effective

recorders of either surface or deep-ocean water compositions.

Fe-Mn oxide crusts and nodules have proven to be effective archives for Nd ue to

high concentrations of Nd, -50 pm (Piepgras and Wasserburg, 1979). There have been a

number of successful studies illustrating that these crusts record deep water Nd values

through time (e.g. Albarede and Goldstein, 1992; Burton and Ling, 1997; Frank and

O'Nions, 1998, Frank et al., 2002). However, there are a few drawbacks to using crusts

and nodules. These deposits have exceedingly slow accumulation rates (on the order of

1-lOmm/Myr; Segl et al., 1984; Puteanus and Halbach, 1988) and their sparse









distribution does not always allow for global sampling (Abouchami et al., 1997; Burton

et al., 1997 and 1999; Ling et al., 1997; O'Nions et al., 1998; Frank et al., 1999; von

Blanckenburg and O'Nions, 1999; Frank et al., 2002). The slow growth rate also makes

dating this archive very difficult. 10Be/9Be and Co have been used to date these crusts

(Frank, 1999); however, this work requires numerous assumptions and Os isotope

chemostratigraphy recently highlighted the errors of some of these age models (Klemm et

al., 2005). Since the growth rate is exceedingly slow the Nd isotopic values of these

crusts can record long term trends of ocean water circulation and have provided

important end member values for many water masses, but they do not record rapid shifts

in circulation associated with many climate events. (Table 2-1).

Phosphates, especially apatites in the form of conodonts and fossil fish teeth, have

proven to be effective archives for Nd isotopes, (Elderfield and Pagett, 1987; Keto and

Jacobsen, 1987 and 1988; Martin and Macdougall, 1995; Martin and Haley, 2000;

Thomas et al., 2003; Martin and Scher 2004; Thomas, 2004; Scher and Martin, 2006).

The hydroxyfluorapatite structure of fossil fish teeth contains 100-1000 ppm Nd, which is

incorporated into the teeth soon after they are deposited on the ocean floor and still in

contact with deep ocean water (Wright et al., 1984; Shaw and Wasserburg, 1985;

Staudigel et al., 1985; Martin et al., 1995, Martin and Haley, 2000; Martin and Scher,

2004). Evidence to support this idea include: 1) fish teeth and Fe-Mn crusts from the

same water mass preserve the same isotopic value (Martin and Haley, 2000), 2) REE

patterns from fossil fish teeth are the same as those for seawater (Elderfield and Pagett,

1986; Reynard et al., 1999), 3) teeth that were found in variable lithologies and pore

fluids, but deposited in the same bottom water have the same isotopic value (Martin and









Haley, 2000), 4) the concentration of Nd in teeth does not increase or decrease with depth

or age of sediments (Bernat, 1975; Elderfield and Pagett 1986; Staudigel et al., 1985;

Grandjean et al., 1987), and 5) teeth that have been deposited in areas of slow

sedimentation and therefore exposed to seawater longer, commonly have higher Nd

concentrations (Elderfield and Pagett, 1986; Staudigel et al., 1986; Martin and Scher,

2004).

Fossil fish teeth, like Fe-Mn crusts, do effectively record the Nd isotopic signal of

bottom water; yet, unlike crusts, teeth can be easily dated with the surrounding sediment

using paleomagnetism, biostratigraphy, chemostratigraphy, and orbital stunning. Because

of this, relatively high-resolution records can and have been produced. Most recently,

fossil fish teeth have been used to create a Nd isotopic record of the Southern Ocean in an

effort to constrain the timing of the opening of the Drake Passage, allowing for a

deepwater connection from the Pacific into the Atlantic (Scher and Martin, 2004

and2006). While fossil fish teeth have been used to produce records with higher

resolution than the records produced from Fe-Mn crusts, there are quite a few drawbacks

to their use as an Nd archive. The process of picking them from sediments and cleaning

them is very time intensive and, more importantly, fossil fish teeth are not widely

distributed temporally and spatially throughout the world's oceans, leaving large gaps in

some records.

Another recently explored archive for Nd isotopes is authigenic Fe-Mn oxide

coatings (Rutberg et al., 2000 and Bayon et al., 2002; Piotrowski et al., 2004). Although

early work with uncleaned planktonic foraminifera determined that these coatings









recorded ocean water Nd isotopic values (Palmer and Elderfield, 1985), this archive has

only recently been further investigated.


-"5

V


Er


I I I I

Cahnduar Ags k-P)
Figure 2-3. ENd from sites in the Atlantic sector of the Southern Ocean spanning 20 kyr to
present, plotted with 6180 values from the GRIP ice core and sea ice
variations from the Western North Atlantic. Variations in the Nd isotopic
record are interpreted to be changes in the strength of NADW and AABW
production over interglacial and glacial timescales. During glacial periods ENd
values are more radiogenic due to a greater influence of AABW to this site,
oxygen isotope values are more negative representing cooler climate, and
there is more sea ice covering the Western North Atlantic (adapted from
Piotrowski et al., 2004).

These coatings occur as a thin veneer of Fe and Mn oxide on the surface of ocean

sediments worldwide and throughout time. Work by Hein et al. (1997) has shown the

mineralogy of Fe-Mn crust to be both ferruginous vernadite and Mn-feroxyhyte. This

coating is essentially a dispersed accumulation of the same material that is concentrated









in Fe-Mn crusts and nodules. Using Pleistocene and younger sediments from the South

Atlantic, it has been shown that these coatings do, in fact, record variations in the flow of

NADW to the Southern Ocean during interglacial/glacial cycles (Rutberg et al., 2000 and

Bayon et al., 2002; Piotrowski et al., 2004). Piotrowski et al. (2004) demonstrated that

Nd isotopic values obtained from Fe-Mn coatings even preserve a record of changes in

deep water circulation on millennial time scales (Figure 4). It has yet to be determined if

this archive can be used for much older sediments.

2.4 Description of Sample Sites

1 0' -150' -120" -90' -0'" -30"' D 30"' 50 90 120" 150' 1a '



30' MB30'







"0-


-80 -- -s
180a -150" -120" -90' -0'" -30' 0' aD' 90" 120" 150" 180'
Figure 2-4. Modem plate reconstruction from the Ocean Drilling Stratigraphic Nework
(www.odsn.de) with DSDP and ODP site locations used in this study. Sites
1259 and 1260 are located in the same area as Site1258.

2.4.1 DSDP Site 608

DSDP Site 608 (42050.205'N, 23005.252'W, 3541.8 m water depth is located on

the southern sife of the King's Trough tectonic complex, which is about 700km northeast

of the Azores (figure 2-4). Hole 608 was drilled to a depth of 530.9 m into to upper

middle Eocene sediments. Samples used for this study ranged from 119.23 to 208.05

mbsf. The section sampled is primarily white foraminiferal nannofossil ooze, with a









carbonate range of 90-95%. The sedimentation rate for this section is 34 m/m.y. and the

age range if from 3.9 to 8.9 Ma. A smear slide summary from hole 608 core 20 indicates

that calcareous nannofossils comprise 78% of the lithology, along with 20% quartz and

2% foraminifers (Ruddiman et al., 1987).

2.4.2 ODP Site 647

ODP site 647 (5319.876'N, 4515.717'W, 3862 m water depth) is located in the

southern Labrador Sea off the southern tip of the Gloria Drift and was drilled to further

investigate deep ocean circulation between the Arctic and the North Atlantic (figure 2-4).

Penetration at Hole 647A was to a depth of 736 m. Sediments used in this study range in

ages from 7.3 to 30.6 Ma with corresponding depths ranging from 116.5 to 158.4 mbsf.

The samples cover 3 different lithologic units, IIA, IIB, and IIIA. Unit IIA, from 116-119

mbsf is a silty clay underlain by nannofossil clay. This unit contains a significant

proportion of nannofossils and towards the bottom becomes a nannofossil clay with

scattered iron/ manganese nodules. The top section (40cm) is composed of 70% clay and

25% quartz silt at the top and 70% clay and 25% nannofossils in the bottom section, with

minor amounts of mica and pyrite. Unit IIB spans from 119 to 135.4 mbsf and consists

of two subunits. The upper subunit consists is composed of a 65% 75% silty clay with

30% quartz including diatoms and spicules. The lower subunit consists of 90% clay

minerals and minor amounts of quartz silt and mica. There is little to no biogenic

carbonate in this section. The percent carbonate for both units is less than 20%

throughout with a sedimentation rate of 46 m/m.y. Finally Unit IIIA consists of a

nannofossil clay and contains both carbonate and biogenic silica. The biogenic

component is 25%-50% and remaining is clay. The average carbonate % for Unit IIIA is

35% with a sedimentation rate of 16 m/m.y. (Shipboard Scientific Party, 1987)









2.4.3 ODP Site 689

ODP site 689 (6431.009'S, 0305.996'E, 2080 m water depth of 2080 m) was

drilled during Leg 113 on Maud Rise, which is a topographic high in the Weddell Sea

(figure 2-4). The deepest drill depth was 297.3m in hole 689B. The sediment sampled

for this project ranged from 60 to 160 mbsf, which equates to an age range of 18 to 40

Ma. From 60 to 72 mbsf the main sediment type is very white to white diatom

nannofossil ooze. The sediment from 72-160 mbsf is dominated by calcareous

nannofossils with radiolarians decreasing downwards through the section. Carbonate

percentages throughout the sampled section range from 51.2-98.5% with an average of

-88% CaCO3. Clay is highly variable throughout the section, with some areas that have

little to no clay content and others that have 60-90% smectite. Sedimentation rates range

from 7 m/m.y. for 18-23 Ma, 4 m/m.y. for 25-33 Ma, and 4.5 m/m.y. for 33-40 Ma

(Shipboard Scientific Party, 1988)

2.4.4 ODP site 690

ODP site 690 (659.629'S, 112.296'E, 2914 m water depth) was also drilled

during Leg 113 to Maud Rise in the Southern Ocean (figure 2-4). The deepest hole was

690B, which recovered 213.4 m. The sediment used in this project ranged from a depth

of 54 to 114mbsf, with ages of 25 to 45 Ma. Lithology from 54-93 mbsf consists of light

grey diatom-bearing nannofossil ooze. Sediment from 93-114 mbsf is almost exclusively

composed of calcareous biogenic sediment, which is primarily white to very pale brown

foraminifer-bearing nannofossil ooze. Throughout the sampled section there are common

(15-30%) to very abundant (60-90%) chlorite, kaolinite, illite, and smectite sections.

Carbonate ranges from 50-85% throughout the sampled section. The sedimentation rate

for 51-93 mbsf is 5.5 m/m.y (Shipboard Scientific Party, 1988).









2.4.5 ODP Site 886

ODP Site 886 (4441.384'N, 16814.400'W, 5713 m water depth) is located on the

eastern edge of the Chinook Trough (figure 2-4). For hole C, which was sampled for this

study, only recovered 72.4 m sediment, but the oldest sediment is Late Cretaceous in age.

Sediment for this project ranged from 64.4 to 70.1 mbsf with ages ranges from 70.1 to 81

Ma (ages were determined using Os isotopes) (Ravizza, personal communication). The

lithology of this section is primarily light to dark brown clay and is described as the

"classic North Pacific 'red' clay". The clay contains 10-30% accessory minerals of

authigenetic and/or digenetic origin. There are ferro-manganese crusts and nodules

throughout the section (Shipboard Scientific Party, 1993).

2.4.6 ODP Site 982

ODP Site 982 (5731.002'N, 1551.993'W, 1134 m water depth) is located on the

Rockall Plateau, which is about halfway between Iceland and Ireland (figure 2-4). It is a

shallow platform at about 1000 m water depth, yet the hole was drilled in a bathymetric

low on the plateau. Drilling reached a depth of 614.9 mbsf in hole B. Samples were

taken from depths of 361.6 to 509.7 mbsf with ages ranging from 10.8 to 15.2 Ma.

Lithology of this section consists primarily of nannofossil ooze with very minor

variations. There are occasional layers of ash and ooze-chalk, but these were avoided

during sampling. Calcareous nannofossils were the most abundant, while diatoms and

radiolarians were very sparse and there were barren intervals throughout the section.

Calcium carbonate averages about 90% throughout the sampled interval. Sedimentation

rates throughout the section average about 35 m/m.y. (Shipboard Scientific Party, 1996).









2.4.7 ODP Site 1050

ODP Site 1050 (305.9953'N, 7614.0997W, 2296.5 m water depth) located on

Blake Nose, on the eastern margin of the Blake Plateau which is due east of Northern

Florida (figure 2-3). Samples for this study were taken from 490 to 597 mbsf, which

represents ages of 77 to 101 Ma. The samples were taken from Units IV and VI, as

defined by the initial reports. Unit 4 extends to 491 mbsf and ranges from a calcareous

claystone with nannofossils present to a nannofossil chalk with clay. Unit 6 extends from

501 to 606 mbsf and is composed of nannofossil chalk or limestone with variable

amounts of clay and claystone. The sedimentation rate for most of this section is -10

m/m.y. The carbonate ranges from 30 to 90 weight percent throughout these sequences

but is generally higher from 500 to 600 mbsf (Shipboard Scientific Party, 1998).

2.4.8 ODP Site 1090

OPD site 1090 (42o54.814'S, 853.998E, 3702 m water depth) is located on the

southern flank of the Agulhas Ridge (figure 2-4). The sediments used in this study

ranged from 73 to 163 mbsf, with an age range of 16.6 to 12.0 Ma. The lithology is

similar throughout the sampled section and consists of a mud bearing diatom ooze to a

mud- and diatom- bearing nannofossil ooze and chalk. The carbonate weight percent is

highly variable ranging from 0-80 wt%, but averages to about 30%. Opal averages to

-15% and terrigenous material is -55% throughout the sampled section. The

sedimentation rate is about 10 m/m.y. (Shipboard Scientific Party, 1999).

2.4.9 ODP Sites 1258, 1259, 1260

ODP Site 1258 (9026.000'N, 5443.999'W, 3192 m water depth), 1259

(917.999'N, 5411.998'W 2354 m water depth), and 1260 (915.948'N, 5432.633'W,

2549 m water depth) are all located on Demerara Rise, off Suriname, South America









(figure 2-4). Site 1258 is the deepest site on the western slope of the rise. This site was

the most heavily sampled of the three for this project. Samples were collected from 375-

450 mbsf, representing an age range of 80-96 Ma. The lithology of the sampled section

spans Units III-V, as denoted by the initial reports (Figure 2-5). Unit III (325- 385 mbsf)

is a calcareous nannofossil clay, with an average of -65 weight percent carbonate. Unit

IV ranges from 385-445 mbsf and is composed of laminated black shale and limestone.

Color variations between these two sediment types record increasing and decreasing

carbonate content, which ranges from 5-95 wto. Finally Unit V is composed of

phosphatic calcareous clay with organic matter. The sedimentation rate across all these

lithologies is ~3 m/m.y. (Erbacher et al., 2004).


o O C oo -r o co o o Age (Ma)


Late Cret ceous
Carrrpanian :-Mastnrctian 4


I I. I m


Calcareous Laminated Pelagic
siltstone black shale chalk

O Calcareous chalk 4t j Nannofossil chalk | Laminated black shale
E CIayitore P- Siltstone [ Sandstone

Figure 2-5. Stratigraphic section of Cretaceous sequence for Site 1258 on Demerara Rise
(Erbacher et al., 2004) showing the three major lithostratigraphic intervals
recovered: early Cenomanian and older faulted, synrift siltstones and
claystones, Cenomanian-early Campanian laminated "black shales", and
Campanian-Paleogene chalk and clayey chalk.


" s
S s g-
i i i i i




C5









Site 1259 is located on the north facing slope of the rise. Samples were taken from

a depth of 441-470.5 with relative ages of 66-70 Ma. The lithology of this section is

composed of nannofossil chalk with clay and calcareous debris with calcareous siltstone

and glauconitic claystone. The carbonate content in this section constitutes -80 wt% of

the sediments and the sedimentation rate is -4.5 m/m.y. (Erbacher et al., 2004).

Finally, site 1260 is on the northwest facing side of the slope. Sampling from this

site ranged from 356-386 mbsf representing ages of 70 to 75 Ma. The lithology is

nannofossil chalk with foraminifera to calcareous claystone. The carbonate in this

section ranges from 45-80 wt%. The sedimentation rate is 4.3 m/m.y. (Erbacher et al.,

2004).














CHAPTER 3
METHODS

3.1 Sample Preparation

3.1.1 Fossil Fish Teeth Preparation

Sediment used for all analyses was obtained from DSDP or ODP. Fossil fish teeth

were handpicked from the >125 |tm size fraction of 50-60 cc samples. The teeth were

cleaned following the oxidative/reductive technique developed by Boyle (Boyle, 1981;

Boyle and Keigwin, 1985). This procedure removes Fe-Mn oxide coatings on the teeth

that could alter the isotopic ratios. Fossil fish teeth have Nd concentrations that range

from 100 to 1000 ppm and analysis can be performed on samples as small as 8 ng Nd.

From each sediment sample 40 |tg or more of teeth, which is generally 3 or more teeth,

were collected and cleaned. The teeth were dissolved in aqua regia to remove any

organic remaining after the cleaning process. After drying down the teeth were

redissolved in 30 jtl of 1.8 N HC1 before they were processed through two cation

exchange columns to isolate Sr and Nd.

3.1.2 Fe-Mn Oxide Coating Preparation

Upon retrieval from ODP core repositories, sediment was thoroughly cleaned

through 63 |tm sieves with deionized water. The sediment samples consist of 0.25 tol g

of >63 |tm size fraction of dry sediment, which was placed into a 50 ml centrifuge tube.

An initial 20 ml of buffered acetic acid solution was added to each sample and the sample

was agitated on an electric shaker until there was no longer a reaction. (ie. the carbonate

no loner reacted). The sample was then centrifuged and the initial 20 ml of acid was









decanted. Then another 10-20 ml of buffered acetic acid solution was added and this

process was repeated until there was no longer a reaction and all the carbonate had been

removed. Samples were then sieved using distilled water through 63 jtm sieves to

remove any remaining clay particles that may have been inside any of the carbonate tests.

Samples were then centrifuged and the water was decanted. Next, 10-15 ml of 0.02 M

Hydroxylamine Hydrochloride (HH) solution was added to each sample to reduce the

oxide coatings. Each sample was then agitated for 1.5 hours and centrifuged for 0.5

hours. The supernatant was removed and placed in clean 50 ml centrifuge tubes, which

were centrifuged again to remove any residual particulate matter. The HH solution was

then removed and divided into two aliquots one for isotopic analyses and the second for

major element and REE analyses.

3.2 Sr and Nd Column Chemistry

Fish teeth samples and Fe-Mn oxide samples were passed through 2 columns to

effectively separate Sr and Nd from the samples. The first column, or Primary column,

used Mitsubishi cation exchange resin with an HC1 eluent and isolated Sr as well as the

bulk REE. The REE cut was dried down and loaded onto the second column, or the REE

column. This column, which separates Nd from other isobars, was packed with

Mitsubishi cation exchange resin and methylactic acid was used as an eluent. Total

procedural blanks are -10 pg of Nd and 100 pg Sr. A second type of REE column was

used for the extracted coating samples. This procedure used an HC1 elution with quartz

columns packed with Teflon beads, which are coated with bis-ethylhexyl phosphoric acid

to separate Nd and Sm from the other REE.









Four of the Cretaceous fish teeth and fish debris samples used in this study were

spiked and analyzed for Sm to determine the 147Sm/144Nd ratios preserved in the teeth.

The range of 147Sm/144Nd values from teeth and fish debris from ODP sites 1050 and

1258 is 0.125, which correlates to corrections of 0.67-0.87 SNd units for this age and

agrees well with values reported by Scher and Martin (2004), Thomas et al. (2004) and

Puceat et al. (2005). The 147Sm/144Nd was also measured on the extracted coating

samples and yielded the same correction. Samples from these sites were corrected and

plotted as SNd(t). For all other samples in this study SNd(o) values were used. For these

same spiked samples the concentration of Nd in the fish teeth samples ranged from 200-

700 ppm, which is well within the range reported for fish teeth (Martin and Scher, 2004).

These concentrations obtained on the TIMS from spiked samples were compared to the

Nd concentrations obtained on the Element by REE analysis on the fish teeth and the two

techniques produced values that fell well within error of one another.

3.3 Nd Analysis

The Nd from small (<200 [tg) fish teeth samples were analyzed on a Micromass

Sector 54 Thermal Ionization Mass Spectrometer (TIMS) at the University of Florida

(UF). Using dynamic mode Nd was measured as NdO, which increases the efficiency of

the analysis. The samples were loaded on zone refined Re filaments using silica gel as a

loader. All ratios are normalized to 146NdO/144NdO = 0.722254. Ideally NdO was then

analyzed for 200 ratios at .5 V 142NdO, but for very small samples the voltage was set as

low as 0.25 V and as few as 100 ratios were counted in order to obtain a measurement.

Errors for all samples are noted in data tables and graphs. The 143Nd/144Nd value for









repeat analyses of the JNdi-1 standard is 0.512102 0.000014 (20). This uncertainty

corresponds to 0.27 SNd units.

Larger fish teeth samples (>200 |tg) and extracted coating samples were analyzed

on a Nu Plasma Multi-Collector Inductively Coupled Plasma Mass Spectrometer

(MC-ICP-MS) at the University of Florida (UF). 0.5 ml of 2% HC1 was added to each

dry sample, then 10 [tl was removed and placed in a sampling beaker. An additional 0.99

ml of 2% HC1 was added to this aliquot and the concentration of the sample was then

tested on the MC-ICP-MS. Ideally 2-5 V of 143Nd was analyzed, and each sample was

diluted appropriately after the first test measurement. The instrument and typical

operating conditions are described in Belshaw et al. (1998). All ratios were normalized

to 146Nd/144Nd = 0.7129 to correct for fractionation. Baselines were measured by ESA

(electrostatic analyzer) deflection of the beam. Under static mode, using the instrument

software both wet plasma using a micromist nebulizer and dry plasma using a desolvating

nebulizer (DSN) were used as uptake systems. Only fairly large samples (>70 ppb) can

be analyzed with wet plasma. When using the DSN a correction factor of 0.000028 or

0.2 SNd unit was applied to samples to make them equate with results using the wet

plasma method. Some samples were measured using time-resolved analysis (TSA),

which produces very precise results with a very small sample size over a much shorter

period of time (Kamenov, unpublished). This method was developed during the data

collection of this project, and, therefore, was only applied for the later analyses. For this

method on-peak-zeros were measured for 30 seconds just before sample introduction.

Data were acquired in series of 0.2 seconds integration over an average of a 60 second

uptake time.










Both TIMS and MC-ICP-MS methods of Nd isotopic analyses were used for data

collection of both fish teeth and Fe-Mn oxide coatings. To compare the results a

correction factor was applied to all data collected on the MC-ICP-MS. Over a day of

data collection on the MC-ICP-MS the JNdi-1 standard was run 5-10 times and averaged.

The difference between this daily averaged value and the 0.512102 value obtained from

the TIMS was used as a correction factor for all data collected on that day. The 20 error

varied daily, falling between .25 and .6 SNd units. Error bars on data plots reflect the

external run error correctly for each machine and each correction method. Due to

variability internal to the MC-ICP-MS it is difficult to develop an overall long-term

calibration. To test the correction method used in this study 11 samples were analyzed on

both instruments and the corrected results all fell within error of one another (figure 3-1).

0.6

0.46---------------- ----------------------------------------
0.4 --- -


z 0.2


0
i 0 U


: -0 .2
--------------------------------- ---- ----


S-0 .42 - -- --- ----- ----^ 4-^ ^ ^ ^-- -----
-0.4


-0.6
0 2 4 6 8 10 12
Number of Samples

Figure 3-1. The difference between the SNd(O) values of 11 samples measured on the
TIMS and the NU-MC-ICP-MS. The line at 0.0 represents samples that
yielded identical values. The fine lines at 0.5 and -0.5 outline the typical error
envelope based on TIMS analyses.









3.4 Major Element and REE Analyses from Fe-Mn oxide coatings

The portion of the extracted coating not used for the isotopic analysis was used for

major element ratios and REE patterns. After the samples were dried down they were

dissolved in 4 ml of 5% HNO3 and left tightly capped on a hot plate overnight.

Approximately 200 [tl of the 4 ml was diluted with -4 ml of 5% HNO3 (for a final

dilution of -2000 times) for analysis on the Element 2 ICP-MS at UF. Each sample had

an uptake time of 1 minute and a wash time of 2 minutes. All REE were analyzed in

Medium Resolution mode, while 24Mg, 27A1, 49Ti, 55Mn, and 56Fe. 23Na and 39K were

analyzed in High Resolution mode. Four runs and four passes or a total of 16

measurements per isotope were performed. For the major elements the error was + 5%

and the blank is negligible. USGS whole rock standards ENDV, as well as a NOD-A and

NOD-P (manganese nodules standards using Axelsson et al., 2002 for the dissolution

method) and an in-house standard of AGV were used as correction factors for both

majors and REEs. Data were normalized first in the Results Editor by checking and

adjusting the calibration curves and second using a drift corrector. The drift corrector,

commonly one of the above standards, was run every 5-8 samples and samples were

adjusted to compensate for any drift during a given analysis. To do this a correction

factor was found between the drifts at either end of sample set and then this correction

factor was multiplied by the unknown sample value and the position of that sample in the

sequence relative to the other samples. Samples measured for major elements were also

corrected using the NOD-A and NOD-P USGS standards. Using the counts for each

sample reported by the instrument the major element ratios were determined. To correct

these ratios the known standard NOD values were divided by the measured NOD values









and all of the unknown sample values were multiplied by these counts to concentration

conversion. A known standard was not identified for the analysis, all standards and

samples were run as unknowns corrected as described. The reported REE for each

sample was then normalized to the weight of the starting sediment sample and to PAAS

(Post-Archean Australian Shale) (Taylor and McLellen, 1985). The error for REE

elements is + 5% and the blank is negliable.

3.5 Sequential Extraction Procedure

The goal of this procedure was to effectively separate the different fractions of

marine sediments and obtain REEs and Sr and Nd isotopic values and concentrations for

each fraction (Bayon et al., 2002). Samples of 0.75 g 0.5 g were weighed out and the

weight was recorded, then each sample was placed in a 50 ml pre-weighed centrifuge

tube. Using a technique similar to that of the extraction procedure defined above, the

carbonate fraction was first removed by adding 40 ml of acetic acid to the centrifuge

tube. The weight of this liquid was accurately recorded for each sample so that

concentrations could be calculated. The sample was agitated until there was no longer a

reaction with the carbonate. The sample was then centrifuged and two aliquots of 5 ml

each of the acetic acid were removed and set aside. One of these samples was used for

REE and major element concentrations and the other was dried down and used for

column chemistry and isotopic analysis. The remaining acid was discarded.

Four times (4x) distilled water was added to the remaining solid material, the

sample was shaken, centrifuged, and the water decanted. This step was repeated twice to

remove all of the acetic acid. The sample was then dried in an oven overnight to remove

any remaining water and reweighed after it was completely dry. The weight difference

between the initial and final weights was assumed to represent the weight of the









carbonate. Once dry, approximately 10 g of 1M HH solution was added to each sample.

Samples were placed in 750 C water bath for three hours and agitated every 30 minutes

(Bayon et al., 2002). This method of extraction was used, as opposed to the one

described above for removal of the Fe-Mn oxide coating for Nd analyses, because Bayon

et al. (2002) determined that this technique removed the whole of the oxide coating more

effectively, leaving the detrital fraction clean for analysis. Once the three hour extraction

procedure was complete the sample was centrifuged and again two 5 ml samples were

removed, one for elemental concentrations and the other was dried for isotopic analyses.

The remaining solution was discarded and the sample was rinsed twice with 4x distilled

water as described above.

The sample was again placed in the oven to dry. In a preliminary study hydrogen

peroxide was used to remove the organic fraction of each sample. In many cases there

was a violent effervescence that caused the loss of some of the sediment. When REE

were measured on this fraction the concentrations were up to three orders of magnitude

lower than the values from the other sediment fractions. Also there seemed to be no

distinct REE pattern for the organic. The organic removal step was subsequently

eliminated and the data presented in this study does not include a distinct organic

fraction.

After the HH step, rinsing, and drying, the remaining sample was removed from the

oven and weighed in the pre-weighed centrifuge tube to determine the amount of

sediment residue. This residue was then powdered using a mortar and pestle and the

sample was split into two portions, one for REE and one for isotopic analysis. For REE

analysis 0.05 g were removed and placed into a beaker containing a drop of 4x water.









One ml of concentrated HF and 2 ml of concentrated HNO3 were then added to each of

the REE samples to dissolve the particulates and then the beakers were tightly capped.

The samples were heated in an oven at 1000C for 24-48 hours, then uncapped and placed

on a hot plate to evaporate. After the samples were dry, 4 g of 5% HNO3 was added to

each. The day before analysis the samples were left on a hotplate uncapped to dry

overnight, then removed and allowed to cool before analysis. For isotopic analysis 0.1 g

of sample was removed and placed in a beaker. To this 1-2 drops of HNO3 and 3 ml of

HF are added and placed on a hotplate for 2 days. Samples are removed and dried down

on a hotplate. Once dry, 2 ml of 6 N HC1 is added to the sample to turn it into chloride

salts. The sample was left on the hotplate overnight, opened and allowed to dry prior to

column chemistry.

3.6 Analysis of Nd and Sr isotopes, and Rare Earth Elements from Sequential
Extractions

For REE patterns samples were analyzed on the ICP-MS using the method

described above for major elements and REE. The weight of the acetic acid or HH

solution and the dilutions were accounted for in the software when analyzing each

sample. The reported values are REE concentrations normalized to PAAS (Taylor and

McLellen, 1985).

The second aliquots of samples were dried down and used for isotopic analysis.

Preliminary tests showed that preparation of the carbonate fraction for column chemistry

was fairly difficult. The samples formed a gelatinous mass (probably a calcium chloride

substance) that would not fully dissolve in the small amount of 0.75 N HC1 used to load

samples onto the columns. Once the samples were loaded a carbonate cap commonly

formed at the top of the resin inhibiting the flow of the eluents. To avoid this problem









the sample was run through the primary columns twice. For the first pass the sample was

dissolved in 1 ml of 1.7 N HC1 and added to the column in 250 [tl increments. After the

sample was loaded 5 ml of 1.7 N HC1 is added to remove most of the Ca. This cut was

discarded and 4.5 ml of 4.5 N HC1 was added to remove the remaining sample including

Sr and REEs. This cut was then dried down and run back through primary columns using

the normal procedure as explained above. The Sr and REE cuts were both collected. The

REE cut was passed through the same columns that were used to elute Nd from the

extracted coatings.

Analysis of the HH aliquot followed the procedure described above for the other

samples treated with HH. The first column eluted Sr and the REEs. Traditional Sr and

REE cation columns were used with AG50W-X12, 200-400 mesh resin with a 3.5N HC1

acid eluent. Both the Sr and REE cuts from the first column were dried down, and the

REE cuts were passed through REE columns, to elute Nd, using the procedure defined

above for the extracted coatings. Sr isotopes were analyzed using the TIMS and Nd

isotopes were analyzed using the TRA procedure on the Nu MC-ICP-MS.

3.7 Sr Analysis

Sr was isolated by two different methods, depending on whether the archive of Sr

was fish teeth, Fe-Mn oxide coatings, or foraminifera. The Sr from fish teeth and Fe-Mn

oxide coating samples was collected from the primary columns as described above,

during the elution to separate Sr and REE. Sr isotopes were also extracted from

foraminifera for dating purposes. Foraminifera were handpicked from >125 |tm size

fraction of 50-60 cc samples. The concentration of Sr in forams is -1000 ppm and the

smallest sample that can be analyzed is -50 |tg Sr. Forams from each sample were









individually broken open and cleaned by sonication with water and methanol.

Foraminifera were then dissolved with HC1 and dried down. Sr was eluted using Sr Spec

resin and 4x H20 following the technique of Pin and Bassin (1992).

Sr cuts from both types of samples were dried down and analyzed on a Micromass

Sector 54 TIMS at UF. Samples were loaded onto Tungsten filaments using Ta205 and

analyzed for 200 ratios at an intensity of 1.5V 88Sr. Fractionation was corrected to

86Sr/"Sr at 0.1194. The 87Sr/86Sr value for repeat analyses of the NBS-987 standard is

0.712025 + 0.000023 (2c). The procedural blank for Sr is -100 pg.














CHAPTER 4
BACKGROUND FOR THE CRETACEOUS STUDY

4.1 General Climate Change and Tectonic Orientations

Extreme climatic, tectonic, and sea level changes made the Cretaceous a very

dynamic and unique time in earth's history, and all may have had a direct effect on ocean

circulation. The Cenomanian was a relatively cool period, but gradually warmed into the

greenhouse conditions of the Cretaceous Thermal Maximum (CTM) during the Turonian.

This was the warmest interval of the last 150 Ma and the peak of the last greenhouse

interval (Frakes, 1994). This interval was characterized by: 1) drastic increases in

poleward heat transport (e.g. Barron et al., 1993; Berner, 1994; Barron et al., 1995;

Frakes, 1994); and 2) CO2 levels that were four times modern values (Poulsen et al.,

1999). Models suggest that poleward heat transport also increased from 15-30% to

explain the reduced equator to pole gradient during the Turonian (Poulsen et al., 1999).

The intense changes in climate, especially the thermal maximum, cannot be directly

related to changes in ocean circulation, but there is undoubtedly some correlation in terms

of changes in circulation patterns and heat transport (e.g., Brass, 1982; Arthur, 1987;

Calvert and Pederson, 1990; MacLeod and Huber, 1996; Frank et al., 1999; Erbacher et

al., 2001; Wilson and Norris, 2001; Leckie et al., 2002; Poulsen et al., 2003; Erbacher et

al., 2005; MacLeod et al., 2005).

Tectonically the Cretaceous was marked primarily by the opening of the North

Atlantic Ocean beginning in the Albian. The opening caused large-scale alterations in

wind patterns and ocean circulation, and brought about changes to global surface









temperatures. Since circulation was fairly restricted the thermal gradients were low

which hindered heat transport. It has been shown through model simulations that the

opening of the North Atlantic, and the gateway between the North and South Atlantic

oceans, could have been a factor in the development of the thermal maximum, as well as

reorganization of ocean circulation and changes to regional climate systems (Poulsen et

al., 2003). During the Turonian midlatitude Westerlies developed along with a 1-150

warming in the polar regions (Bice and Marotzke, 2001). Simultaneously, the opening of

this seaway reduced the regional equator-to-pole temperature gradient by as much as 150

C. This caused cooling at the equator, and possible production of warm saline bottom

water (Poulsen et al., 1999).

4.2 Cretaceous Ocean Circulation

Both changes to plate configuration and changes in global surface temperatures

seemed to effect ocean circulation to some degree, however it is very difficult to

constrain this circulation. Using general circulation models there is evidence that the

opening of the gateway between the North and South Atlantic in the Late Albian, had a

large effect on circulation (e.g. Barron and Peterson, 1989). Prior to this opening there

were extremely warm and saline conditions in both the North and South Atlantic Oceans.

After the opening there is evidence that Antarctic Bottom Waters fed into the Atlantic, as

well as the Pacific and Indian Oceans, driving thermohaline circulation in these basins

(Haupt and Seidov, 2001; Poulsen et al., 2001). Contrary to this conclusion, the presence

of warm saline bottom waters originating at low latitudes has been identified by

comparing 6180 values of planktonic and benthic foraminifera (e.g., MacLeod and Huber,

1996; Barrera and Savin, 1999).









By the Maastrichtian there is also evidence of intermediate and deep water forming

in the high-latitude Southern Ocean and the northern Atlantic which flowed throughout

the ocean basins inferred from changes in 613C from benthic foraminifera (e.g., Frank et

al., 1999; D'Hondt and Arthur, 2002). The limited number of deep sea drill sites that

penetrated to this age and concerns about preservation of carbon and oxygen isotopes

limit what can be determined from these methods. Modeling simulations produce results

that are also contrary to the above conclusions suggesting that there was no deep water

connection between the North and South Atlantic oceans until after the Cenomanian

(Handoh et al., 2003). Needless to say, there are very few constraints on ocean

circulation throughout the Cretaceous.

The Mid-Cretaceous opening of the North and South Atlantic Oceans created a

complicated ocean bathymetry. There is evidence of secluded basins (e.g. Demarara,

Sierra Leone, and Guinea) and large sills that could have interrupted deep sea circulation

(Jones et al., 1995). There were also large offset fracture zones and transverse ridges,

which may have restricted flow (Bonatti et al., 1994; Handoh et al., 1999).

4.3 Ocean Anoxic Events

In addition to the large perturbations in temperature and CO2 and critical plate

reconfigurations, the Cretaceous is marked by dramatic perturbations to the global carbon

budget recorded as ocean anoxic events (OAEs). Theses events are distinguished by

ocean-wide and regional changes from normal pelagic sediments to organic-rich black

shales, which were deposited in oxygen deficient waters. They are recognizable by large

increases in total organic carbon content and a large positive 613C excursion in both

organic and inorganic carbon (e.g., Arthur et al., 1990; Bralower et al., 1994). Other









evidence of large-scale changes to ocean chemistry is illustrated by extinctions of some

nannoplankton species, which are attributed to these anoxic events (e.g. Wonders et al.,

1980; Kuhnt et al., 1986; Jarvis et al., 1988; Erbacher and Thurow, 1997). Six distinct

OAEs have been recognized throughout the Late Cretaceous (OAEla-d, OAE2, and

OAE3), two of which can be identified on a global scale, OAEla and OAE2. These

events represent relatively brief periods of time (105-106 years) (e.g. Sageman et al.,

2006) and must have been caused by large scale changes to the ocean environment, yet

the ultimate cause is still highly debated.

OAE2, or the Bonarelli Event, which falls at the Cenomanian Turonian boundary

about 93.5 Ma falls right at the height of the Cretaceous greenhouse and represents the

largest perturbation to the global carbon cycle in the last 250 Ma. It is characterized by

laminated organic-rich silt and claystone with no evidence of benthic fossils. Although

this event has been studied in numerous global localities, the cause of anoxia during this

OAE, as well as all the others is still unknown. The prevailing theories simply stated are

that the anoxia can be attributed to either: 1) a surface down phenomenon, such as a sharp

increase in surface productivity, or 2) a bottom up phenomenon, denoted by deep water

stagnation that could lead to enhanced preservation.

The surface down argument states that the warm humid conditions of the

Cretaceous led to enhanced physical weathering of the continents and an accompanying

increased delivery of nutrients to the ocean, resulting in enhanced surface productivity

and organic carbon burial (e.g., Pederson and Calvert, 1990; Calvert and Pederson, 1992;

Erbacher and Thurow, 1997; Wonders, 1980; Kuhnt et al., 1986; Jarvis et al., 1988;

Weissert 1989). Other models called on enhanced upwelling (Kolonic et al., 2005) or









volcanic production of nutrients in a surface plume (Sinton and Duncan, 1997; Snow et

al., 2005), but the premise is the same; excess surface productivity generated an organic

rain rate than exceeded the capacity of the deep ocean to oxidize the material.

The opposing mechanism for OAE formation calls upon enhanced preservation due

to changes in deep water properties, notably warmer bottom water temperatures, lower

oxygen concentrations, and/or slower deep circulation leading to stagnation. This model

is based on the assumption that high sea level and changes to thermohaline circulation

caused a decrease in the subsurface oxygen concentration and subsequent expansion of

the oxygen minimum zone (OMZ) (e.g. Bralower and Thierstein, 1984; Herbin et al.,

1986), which resulted in the increased burial of organic carbon (e.g., de Greciansky,

1984; Arthur, 1990). Changes to circulation could have been caused by warmer surface

water temperatures at the poles, which decreased the formation of cold bottom water and

increased the amount of warm, high salinity bottom waters that formed at lower latitudes

(Sinton and Duncan, 1997). Alternatively, ocean circulation models suggest that deep

water continued to form in the high latitudes as the water there was still cooler than at the

lower latitudes although it was warmer than modern high latitudes (Bice et al., 2001)

Benthic foraminifera 6180 values support the idea of warmer bottom water

temperatures at this time, -20C compared to -120C during the late Albian (Huber et al.,

2002) and 2C today. This warm water would contain less dissolved oxygen, and might

indicate more stagnant deep water circulation (Savin, 1977; Erbacher, 2001). Sageman

and Meyers (2002) illustrated that peaks in 613C values can precede or follow the peaks

for total organic carbon (TOC) for OAE2. This suggests the anoxia does not simply

result from oxygen depletion due to high organic carbon rain rates. Herrle et al. (2003)









examined the forcing mechanism of black shale formation during OAE1 and found

variations between oxygen isotopes, and calcareous nannoplankton, palynomorph, and

benthic foraminifera assemblages that reflect changes to climatic conditions. The study

concluded that these variations were caused by feedback mechanisms within a monsoonal

climate system, which involve warm/humid and cool/dry cycles. They argue that the

black shale formation and deep water anoxia occurred during humid conditions when

high precipitation and low evaporation resulted in decreased deep water formation and

stagnation.

Another popular theory for the cause of anoxia focuses on changes in ocean and

atmospheric chemistry caused by the eruption of large igneous provinces (LIPS), namely

the Caribbean province and/or an increase in hydrothermal activity associated with

increased ocean crust production, both of which coincide with OAE2 (Arthur et al., 1997;

Weissert, 1989; Larson, 1991; Sinton and Duncan, 1997; Kerr, 1998; Jones et al., 2001;

Brumsack, 2005; Snow et al., 2005). Weissert (1989) argues that increased subsurface

volcanism put excess CO2 into the atmosphere, which in turn accelerated continental

weathering increasing the supply of nutrients to the oceans. Another argument suggests

that the subsea eruption was so large that the buoyant hydrothermal plume brought

limiting nutrients in the form of dissolved metals to the surface of the ocean, resulting in

drastically increased surface productivity (Sinton and Duncan, 1997; Snow et al., 2005).

These LIPS eruptions are believed to have been 3 orders of magnitude larger than the

largest mid-ocean ridge event (Sinton and Duncan, 1997) and the increase in 02

consumption by the oxidation of sulfides and metals could have overwhelmed the poorly

oxygenated water below the mixed layer leading to brief periods of seawater anoxia and









the extinction of some bottom dwelling organisms. Plate reconstructions for this time

highlight an open gateway in the current Caribbean region, connecting the Atlantic and

Pacific (Lawver et al., 1994; figure 4-1). This configuration would have assured that

events in the Pacific influenced at least the northern Atlantic (Sinton and Duncan, 1997).
















90 Nb PLATESAJTIG
Turonian (Late Cretaceous) August 2002


Figure 4-1. Tectonic plate reconstruction at 90Ma showing the open connection between
the Atlantic and Pacific Oceans (Lawver et al., 1994)

Interestingly, a number of the OAEs throughout the Mesozoic coincide with large

perturbations to the Sr isotopic curve (figure 4-2). The OAEs that occurred during the

Jurassic, the Early Aptian, and the Cenomanian-Turonian (OAE2) all have sharp

nonradiogenic excursions in the 87Sr/"Sr value (Jones and Jenkyns, 2001). The most

probable cause for these excursions is the increase in hydrothermal activity associated

with the eruption of LIPS and crust production (figure 4-3). Given that OAE events

punctuate a long interval of increased crustal production, Jones and Jenkyns (2001)

suggest that the increased nutrients and CO2 from these out-gassing events simply

preconditioned the oceans for anoxia, but there had to be another simultaneous variable,

such as sea level change, that pushed the ocean into complete anoxia.



















U





v.mmt


Figure 4-2. The seawater Sr isotope curve with 3 OAEs that coincide with perturbations
in the Sr isotopic values (from Jones and Jenkyns, 2001).


E1 L: 1 1 I l& I M1 IP
Ago IM


Figure 4-3. Relative ocean crust and plateau production over time. The line represents
the position of OAE2 (adapted from Jones and Jenkyns, 2001). Production
rates from 120 to 80 Ma are higher than the preceding or subsequent intervals.

A dramatic sea level rise (Figure 4-4) also coincides with OAE2 and OAE3 and

increased ocean crust production (Haq et al., 1988; Jenkyns, 1991). Erbacher and

Thurow (1997) proposed that this increase in sea level drowned carbonate platforms,









thereby leaching nutrients into the oceans, which in turn caused an increase in primary

productivity. Given that OAEs are isolated, relatively short events, Jones and Jenkyns

(2001) proposed that global warming associated with hydrothermal activity and crust

production may have preconditioned the ocean, while sea level rise provided the final

trigger for the event.


~ II

I 21i

II!)L

i


S 1 l IE TINBhI E l I. -r :IpI i IN I J N H


|I !j! M J LJ I enCMt J1t c- OIWI l* Inlu
2M .. 10 W g
Ago 041

Figure 4-4. Eustatic sea level curve of the last 200 Ma. The line represents the position
of OAE2 and correlates fairly well to a sea level high stand (adapted from
Jones and Jenkyns, 2001).

Among the many theories for enhanced anoxia during the Late Cretaceous, the

most popular theories rely on 1) increased productivity or 2) increased preservation as a

function of a change in circulation, and it has been difficult to distinguish between the

two. Nd isotopes have been shown to effectively record changes in ocean circulation

independent of changes in productivity. By obtaining a record of Nd values over an

anoxic interval, it may be possible to test whether changes in deep ocean circulation were

related to periods of anoxia. If there is no change in Nd values it could be imply that

OAEs were caused chiefly by an increase in surface production.
















CHAPTER 5
RESULTS FROM THE CRETACEOUS OAE STUDY

The 613Corg values measured at site 1258 on Demerara Rise (figure 2-4) record the

large positive excursion typical of OAEs during both OAE2 and the Mid-Cenomanian

event (figure 5-1; table 5-1). This work will primarily focus on the OAE2, which spans

from 422.26 to 423.81 mcd, but the Mid-Cenomanian Event (MCE), another anoxic

event, is also clearly distinguishable at 448.18 mcd. Both events record excursions of -6

%o (MacLeod, unpublished data), which is the same shift documented by Erbacher et al.

(2006). The total organic carbon (TOC) jumps from -13% to nearly 30% during OAE2

(figure 5-1).

-20 30
A TOC%


-22 13C org 25



-24 ---- 20
C --
0
> o

S -26 ---- 15



-28 10



-30 5
410 420 430 440 450 460 470 480 490
mcd
Figure 5-1. 613C and TOC % from ODP Site 1258 from 410-490 mcd. The green box
from 422-424 mcd represents OAE2 and the aqua box is the MCE spanning
from 448 to 453 mcd.










Table 5-1. Site 1258 mcd and 613C
mcd 613C vs VPDB
414.78 -27.09
414.83 -26.92
415.11 -24.33
416.77 -27.19
418.24 -27.20
420.29 -27.10
421.51 -27.36
421.81 -27.12
422.09 -26.31
422.26 -21.99
422.62 -23.51
422.96 -22.32 OAE2
423.22 -22.53
423.81 -22.25
425.71 -27.22
426.44 -28.48
427.32 -28.50
427.48 -28.09
428.30 -28.12
428.36 -28.27
429.60 -28.24
445.43 -28.75
448.18 -21.89 MCE
450.22 -27.39
452.53 -28.97
456.04 -28.36
462.68 -28.92
467.33 -28.68
481.87 -29.02
Unpublished data from McLeod.
To determine whether there was a change in ocean circulation associated with

OAE2 and the MCE in the North Atlantic SNd(t) was measured for Site 1258 over the

interval encompassing both carbon isotope shift. Neodymium isotopes were sampled

from 375 to 480 mcd at fairly low resolution, averaging about every 30 kyr. The SNd(t)

values prior to MCE and between the MCE and OAE2 were fairly nonradiogenic with

values as low as -16 and as high as -13 SNd units (figure 5-2; table 5-2). The largest

anomaly prior to OAE2 is the large peak that coincides with the MCE at 448.18 mcd











where the SNd(t) value spikes to -10.6. After OAE2 SNd(t) values drop back to


nonradiogenic values of-13.5 to -17.8.


-20


-22


-24
o
C)

-26


-28


-30


-8

-10

-12

-14

-16

-18


380 400 420 440 460 480


Figure 5-2. SNd(t) and 613C values from Site 1258 from 370 to 490 mcd. The green box
represents OAE2 and the aqua box represents the MCE.

During OAE2 SNd(t) values increase dramatically by nearly 8 SNd units peaking at -


8.2. This transition occurred fairly rapidly and is tightly correlated to high resolution


613Corg results for the same core (Erbacher et al.,2005) (figure 5-3). The rate of increase


at the start of the event is very similar between the two proxies and the peak of each falls


within 130 cm; SNd peaks at the onset of the event at 425.29 mcd and 613Corg peaks at


425.16 mcd. Based on 613Corg Erbacher (2005) defines the anoxic interval between 422







46


to 426 mcd. The SNd excursion falls almost precisely within these limits (421.8 to 426

mcd) and the small discrepancy that exists may be a function of sampling frequency.

-6 -18
[ Nd (t) 13C
org
-8 -20


-10 ------ -22


-12 --- -- -24 o


-14 -26


-16 -28

-16 ------------------------ -----------------------------

-18 -30
420 421 422 423 424 425 426 427 428
mcd

Figure 5-3. High resolution 613Corg from Erbacher et al., 2005 with the SNd(t) values
spanning OAE2 (420-428 mcd) from ODP Site 1258.

To determine the distribution of Nd isotopes during the Mid-Cretaceous fish tooth

or fish debris samples were also analyzed from Site 886 in the Pacific Ocean and Site

1050 at Blake Nose (figure 2-4). Low resolution sampling from these sites illustrates that

values from 70 to 81 Ma at Site 886 were more radiogenic than any other site sampled in

this study, ranging from -4 to -5.5 (figure 5-4; table 5-2). Samples from 95 to 102 Ma at

Blake Nose (Site 1050) also yielded relatively radiogenic SNd(t) values of -5, but ranged

down to -9.5 at 77 Ma.

Sites 1259 and 1260 with present water depths of 2354 mbsl and 2549 mbsl

respectively represent shallower locations than Site 1258 (present water depth of 3192







47



mbsl). Samples were analyzed from these sites to determine whether the very negative


SNd values observed at Site 1258 were unique. From -66 to 71 Ma Site 1259 yielded


values that ranged from -15 to -16.5 SNd units. Site 1260 samples yielded relatively


consistent values around -16 from 70 to 75 Ma. At 70 Ma data points from 1260 and


1259 are within error of one another at a value of -15.85 SNd units.


-14


-16


-18
65


Figure 5-


EB-

- --------

o--




^ /-A ^_


\^ -- ~^ --- --- --


.4


--886
1259
1260
1258
1050
SSoudry 2004
SPuceat 2005


70 75 80 85 90 95 100
Ma

Nd(t) values from Site 886 in the Pacific Ocean, Sites 1259, 1258, and 1260
from Demerara Rise, and Site 1050 from Blake Nose spanning 65-103 Ma.
The green box represents OAE2 and the aqua box shows the position of the
MCE. Additional data includes SNd values from the Negev in Israel (Soudry et
al., 2004) and Tethyan values from France (Pucaet et al., 2005).







48



Table 5-2. Sr and Nd values from Cretaceous Samples from ODP Sites 886, 1050, 1258,
1259, 1260
Sample name mcd Age (Ma)1 8Sr'86Sr2 4"44Nd3 SNd(o)4 6Nd(t)5 147Sml44Nd


Pacific
886-C 8-1 60 64.40
886C 8-1 112.5 64.90
886-C 8-2 122.5 66.50
886C 8-3 122.5 68.00
886C 8-4 122.5 69.50
886-C 8-5 113 70.93
886C 8-6 52 71.82
AtlanticlBlake Nose
105020-1 33 490.63
1050 27-2 103 558.25
1050 29-2 102 577.45
1050 31-2 103 596.65
AtlanticlDemeraraRise


1258A 38-1 105A
1258A 42R -1 8
1258A 42R-1 65
1258A 42R-3 60
1258B 45R-1 95
1258B 45R-1 95
1258B 45R-1 96
1258B 45R-3 36


375.20
414.83
415.40
418.24
419.28
419.28
419.29
420.54


1258B 45R-3 51 420.69
1258A42R-5 12 421.29
1258A 42-6 2 421.51
1258A 42-6 32 421.81
1258A 42-6 60 422.09
1258A 42R-6 65 422.14
1258A 42R-6 95 422.44
1258A 42R-6 115 422.64
1258A 42R-7 7 422.96
1258A 42R-7 25 423.14
1258A 42R-7 70 423.59
1258A 42R-7 92 423.81
1258C 17X-1 85 425.29
1258C 17X-1 105 425.49
1258C 17X-1 125 425.69
1258C 17X-2 10 425.93
1258C 17X-2 30 426.13
1258C 17X-2 70 426.53
1258B 47R-1 23 430.40
1258B 48R-1 111 436.45
1258B 49R-1 44 439.20
1258B 49R-3 30 441.73
1258A 45R-2 57 445.43
1258A 46R-1 0 448.18
1258A 46R-2 68 450.22
1258A 46R-4 33 452.53
1258A 47R-1 12 456.04



Table 5-2. Continued


70.1
71.5
71.5
75.8
77.8
80
81


77.00
98.30
99.73
101.30

80.00
92.62
92.67
92.90
93.04
93.04
93.05
93.10
93.18
93.21
93.24
93.28
93.29
93.32
93.35
93.37
93.40
93.42
93.46
93.48
93.52
93.53
93.55
93.57
93.60
93.70
93.90
94.50
94.97
95.21
95.40
95.50
95.60
96.00
96.59


0.70795 2.3E-05

0.70796 2.3E-05


0.70812 2.3E-05


0.70758 2.3E-05
0.70753 2.3E-05

0.70755 2.3E-05


0.70759 2.3E-05


0.70757
0.70757
0.70759

0.70760
0.70760
0.70774


2.3E-05
2.3E-05
2.3E-05

2.3E-05
2.3E-05
2.3E-05


0.70760 2.3E-05






0.70764 2.3E-05


0.512389
0.512356
0.512392
0.512415
0.512395
0.512382

0.512179
0.512349
0.512334
0.512337

0.511804
0.511824
0.511872
0.511899
0.511724
0.511748
0.511849
0.511864
0.511783
0.511841
0.511945
0.511846
0.511940
0.512028
0.511938
0.511921
0.511967
0.511978
0.512175
0.512074
0.512145
0.512120
0.511841
0.511847
0.511805
0.511766
0.511917
0.511764
0.511822
0.511853
0.511822
0.512049
0.511859
0.511812
0.511873


-4.86
-5.51
-4.80
-4.35
-4.75
-4.99

-8.95
-5.64
-5.93
-5.87

-16.27
-15.88
-14.95
-14.42
-17.83
-17.36
-15.39
-15.10
-16.67
-15.55
-13.52
-15.45
-13.62
-11.90
-13.66
-13.99
-13.09
-12.87
-9.03
-11.01
-9.62
-10.10
-15.55
-15.43
-16.25
-17.01
-14.06
-17.05
-15.92
-15.32
-15.92
-11.49
-15.20
-16.11
-14.93


-4.19
-4.84
-4.13
-3.68
-4.08
-4.32

-8.44
-4.77
-5.06
-5.00

-15.44
-15.01
-14.08
-13.55
-16.96
-16.49
-14.52
-14.23
-15.80
-14.68
-12.65
-14.58
-12.75
-11.03
-12.79
-13.12
-12.22
-12.00
-8.16
-10.14
-8.75
-9.23
-14.68
-14.56
-15.38
-16.14
-13.19
-16.18
-15.05
-14.45
-15.05
-10.62
-14.33
-15.24
-14.06


0.1250


0.1256





















0.1262

0.1218











1258C 27R-2 0
1258C 32R-CC
1259
1259B 13R-1 114
1259B 13R-7 40
1259B 14R-2 90
1259B 15R-1 76
1259B 15R-3 58
1259B 15R-6 70
1259B 16R-1 56
1260
1260A 39R-1 78
1260A 40R-1 109
1260A 40R-3 104
1260A 42R-2 77


480.29
505.95

441.91
442.60
452.06
458.90
459.03
459.64
470.98

357.12
369.05
372.00
389.89


98.93 0.70755 2.3E-05
101.00 0.70759 2.3E-05


66.00
67.00
68.00
69.00
70.00
71.00
72.00

70.10
72.30
72.90
75.00


0.70772 2.3E-05
0.70770 2.3E-05
0.70771 2.3E-05
0.70766 2.3E-05


0.511935 -13.71 -12.84 0.25


0.511837 -15.63 -14.96 0.32
0.511833 -15.70 -15.03 0.32
0.511758 -17.17 -16.50 0.32
0.511800 -16.35 -15.68 0.32
0.511794 -16.46 -15.79 0.32
0.511844 -15.49 -14.82 0.32
0.511836 -15.64 -14.97 0.32

0.511788 -16.58 -15.91 0.25
0.511776 -16.81 -16.14 0.25
0.511801 -16.33 -15.66 0.25
0.511783 -16.68 -16.01 0.25


1 Ages for Site 886 from Ravizza, unpublished data.; for Site 1050 from Shipboard Scientific Party,
1998; and for Sites 1258, 1259, 1260 from Erbacher, 2004.
2 Measured Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (20) and normalized to
86Sr/88Sr= .1194
3 143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and are
then normalized to Jndi-1 = 0.512103 (TIMS average)
4. SNd(o) 14[(Nd/144Nd)sample/( Nd/ Nd)cHUR-1] X 104
5. SNd(t) [(143Nd/144Nd)sample(t)/( 14N / Nd)HR(t)-l] X 104 using 14Sm 144Nd














CHAPTER 6
DISCUSSION OF CRETACEOUS OAE STUDY

The SNd values for the Cretaceous study were derived from fossil fish teeth and fish

debris. An important consideration for material of this age is whether these values

represent contemporaneous bottom waters, as they do for younger samples (e.g. Staudigel

et al., 1985; Martin and Scher, 2004), or if the values have been influenced by diagenetic

alteration. There are several lines of evidence to suggest that the shift seen in the SNd

values at Site 1258 does, in fact, represent a change in ocean water mass. Firstly, the

lithology across the OAE2 and the MCE intervals is consistent. For 15 Ma throughout

the Cenomanian and Turonian thinly laminated, organic- rich black shales were

deposited, with no change in lithology. The primary lithologic boundary occurs instead

in the Late Campanian; however, background values are the same before and after this

change. Thus, there is no lithologic change associated with the large shift in Nd isotopes,

and no Nd isotopic change associated with the lithologic boundary.

Secondly, the large positive excursion in the Nd isotopes could be created by

diagenetic alteration from young volcanic material. To test this theory Sr isotopes were

analyzed from the fish teeth and debris, with the expectation that alteration in the

presence of volcanic ash would produce a corresponding shift in the 87Sr/86Sr value

toward less radiogenic values. Strontium isotopes measured in fossil fish teeth from Site

1258 are much more radiogenic than the 87Sr/86Sr seawater curve. Figure 6-1 illustrates

that the Sr isotopes preserved in the fish debris are shifted toward continental values

rather than young volcanics.










0.7078
sea water EOAE2-
fish teeth
0.7077 -


0.7076 -
Alteration toward |
continental material
0.7075 -


0.7074


0.7073
Alteration toward volcanic
85 90 95 100
Ma
Figure 6-1. 87Sr/86Sr seawater curve from 85-100 Ma (Jones and Jenkyns, 2001) along
with the Sr isotopic values from fossil fish debris collected from Site 1258.

REE patterns measured on fish teeth and debris provide further support for the

lack of diagenetic alteration. REE were measured from samples before, during, and after

OAE2 to determine if there was any change across this interval. If the anomaly were

caused by diagenesis (suggesting that the excursion during the event was the product of

young volcanic input), the REE patterns from before and after the excursion might be

expected to be different from the pattern during the event. In particular, samples affected

by diagenesis in the sedimentary environment would be expected to have flatter REE

patterns typical of shale or terrestrial inputs, when normalized to PAAS. However, all of

the samples have MREE enrichment relative to shale, suggestive of REE fractionation

into apatite (figure 6-3) (e.g. Reynard et al., 1998) and do not seem to be influenced by

volcanics, which would be recorded as an enriched HREE pattern. All the samples also

have a similar Ce anomaly indicating that they were deposited under similar redox

conditions (Grandjean et al., 1987; Lecuyer et al., 2004).







52


1000



100 -------



1 0 - -- -- - -





0
Z
0.1 -- -------AE-I
0.1AE
0 pre-OAE
IU post-OAE
--,-- se water

0.01
La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu

Figure 5-3. REE plots of modern seawater (De Baar, 1985) compared to samples from
before, during, and after OAE 2. All profiles are normalized to PAAS shale
(Taylor and McLellen, 1985). REE pattern for modem seawater from 3000 m
(De Baar et al., 1985).

Table 6-1. REE values from Fossil Fish Teeth Samples from Before, During and After
OAE2
Sample La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu
Before 31.627 25.021 38.072 43.610 46.467 53.721 70.377 48.386 36.923 21.381 19.013
Before 19.783 14.621 19.929 22.743 24.579 26.793 30.578 23.436 20.399 16.058 15.377
Before 21.763 11.017 16.478 18.864 18.523 22.857 25.400 20.858 21.670 17.769 17.697
During 67.776 47.387 68.525 80.871 85.371 103.068 115.327 97.000 92.685 66.885 61.319
During 57.743 44.318 67.019 79.922 98.529 134.449 131.601 120.295 111.479 69.611 57.463
After1 26.329 15.998 20.565 22.116 22.190 26.310 32.652 25.814 31.092 33.689 31.451
After 15.304 10.725 15.453 17.590 18.638 21.386 23.660 20.456 20.849 17.741 17.354
After 10.477 8.667 11.607 13.316 14.463 17.076 19.479 15.609 14.354 11.517 10.835
Notes: 1Sample values multiplied by 10
Error is 5%

Finally, diagenetic alteration of the Nd isotopes might be expected to coincide with

lithologic boundaries. The Late Cretaceous section measured for this study has a very

consistent lithology of black shale, which continues from 92.6 to 98.5 Ma and crosses the

Cenomanian-Turonian boundary and OAE2. The largest change in lithology in the

interval of interest occurs at 415 mcd at the hiatus/condensed interval that separates the









black shale from chalk (figure 2-3). There are undoubtedly changes in diagenetic

conditions across this boundary, yet the SNd values are unaffected (figure 4-2)

The SNd(t) values reported at Demerara Rise, from Sites 1258, 1259, and 1260,

before and after OAE are extremely nonradiogenic (-14 to -17). These values are lower

than any other values reported over this time period, suggesting that there was a separate

and distinct water mass bathing this site. Published SNd values for the Late Cretaceous

include values of -2.5 to -5.5 for the central Pacific (Thomas, 2004; Frank et al., 2005)

and values of -7 to -12 for the Tethys (Stille and Fisher, 1990; Soudry et al., 2004; Puceat

et al., 2005). Values from Puceat (2005) and Soudry (2004) are plotted on figure 5-4

and represent a distinct water mass from the one bathing Demerara Rise before and after

the anoxic events. However during the events the excursions at Site 1258 are similar to,

although slightly less radiogenic than, these Tethyan water masses. The background

values reported in this study are also lower than the modern North Atlantic, which has the

most nonradiogenic value for a major modern water mass, with values of about -13 (e.g.

Piepgras and Wasserberg, 1987; Lacan and Jeandel, 2005), and lower than any other

reported SNd value for a major water mass in the Cenozoic (Burton et al., 1997; Ling et

al., 1997; O'Nions et al., 1998; Burton et al., 1999; Frank, 2002; Thomas et al., 2003;

Scher and Martin, 2004; Soudry et al., 2004; Thomas, 2004; van der Flierdt et al., 2004;

Frank et al., 2005; Scher and Martin, 2006).

During the Late Cretaceous the North Atlantic was a young ocean with large sills

and ridges that could have restricted deep circulation (Bonatti et al., 1994; Jones et al.,

1995; Handoh et al., 1999). In particular, there is evidence that there was no deep

connection between the North and South Atlantic at this time (Kennett, 1982; Frank and









Arthur, 1999). The nonradiogenic values from Demerara suggest that this may have been

a relatively isolated basin that was affected by proximal weathering from the South

American continent. Local weathering of the Trans-Amazonian Proterozoic Shield or the

Archean Guiana Highland would have introduced nonradiogenic Nd into the bottom

waters in this region (White and Dupre, 1985). This idea of an isolated basin around

Demerara is further supported by the ENd values at Blake Nose that are much more

radiogenic over this period, suggesting they may have been influenced by the open flow

between the North Atlantic and the Pacific (figure 5-4).

The most intriguing aspects of the ENd data from Demerara Rise are the large ENd

positive excursion of 8 units and the close, if not exact, correlation to the 613Corg

excursion during OAE2, as well as the MCE. OAE2 spans about 4 m of sediment at Site

1258 and is believed to represent 563-601 k.y. based on an orbitally tuned record

(Sageman et al., 2005). Given that the ENd excursion is not the result of diagenetic

processes, the most likely cause is a change in deep water circulation at this site during

the anoxic event. This conclusion argues against the theory that OAE2 is caused by an

increase in primary production (e.g., Pederson and Calvert, 1990; Calvert and Pederson,

1992; Erbacher and Thurow, 1997 Wonders, 1980, Kuhnt 1986, and Jarvis, 1988,

Weissert 1989), as productivity alone would not alter the ENd value. In addition, the Nd

isotopic evidence that Demerara Rise is located in an isolated basin before and after

OAE2 argues that OAE2 is not the product of increase in preservation caused by deep

water stagnation (Savin, 1977; Erbacher, 2001). Instead the ENd changes at this site

indicate a rapid onset of mixing or changes to flow patterns concurrent with changes to

the carbon isotopes. Any theory for the formation of OAE2 must take into account the









shift to radiogenic ENd values over the event and the correlation to the positive shift in

613C values, which implies an increase in productivity and/or preservation. There are few

hypotheses presented in the literature that would explain both of these proxies.

One possible explanation of the data is that the sea level transgression across the

Cenomanian- Turonian boundary (Jones and Jenkyns, 2001) may have led to a

connection between deep waters at Demerara Rise and Blake Nose. Mixing between the

Blake Nose endmember (-5) and the Demerara endmember (-16) could produce the

observed excursion value of up to -8 ENd. In terms of 613C, the sea level rise would have

drowned continental shelves thereby releasing nutrients into the ocean and leading to

increased productivity, which in turn caused the anoxia (Haq et al., 1988; Jenkyns, 1980;

Jenkyns, 1991). Thus, a rise in sea level could explain both the enhanced deep water

circulation and increased surface productivity. Jenkyns (1980) found evidence of rapid

sea level rise in both the Western Interior Seaway (WIS) and in Northern Europe

associated with both OAE2 and OAE3. The transgressive events appeared to have

relatively short durations similar to those of the OAEs; however, the ages were poorly

constrained. Although the highstands in the WIS and Northern Europe seem to peak

during OAE2, the global sea level record peaks at the end of the event (Jenkyns, 1980).

An additional problem with this theory is that every sea level rise is not associated with

an OAE and some of the OAEs (e.g. OAElc) are not associated with a sea level

transgression (Jones and Jenkyns, 2001). In this scenario, the ocean at the time of the

Cretaceous OAEs must have been preconditioned by some other mechanism so that sea

level rise could have such a dramatic effect.









Another proposed mechanism for OAEs is the drastic increase in ocean crust

production or Caribbean LIP formation (Sinton and Duncan, 1997; Jenkyns and Jones,

2001; Leckie et al., 2002; Snow et al., 2005). This eruption would have: 1) increased

CO2, which in turn would lead to an increase in primary production and continental

weathering, and 2) increased nutrients associated with hydrothermal venting or enhanced

continental weathering, thereby leading to increased production (Vogt, 1989; Erba, 1994;

Kerr, 1998; Jones et al., 2001; Leckie et al., 2002; Snow et al., 2005). This increase in

productivity would account for the increased 613Corg values and the increased organic rain

would lead to anoxia. In terms of Nd, the SNd value of oceanic basalt is -+10, thus the

shift in Nd isotopes observed at Demerara Rise could reflect the input from basalt

weathering or hydothermal inputs. There are two assumptions associated with this

theory. Firstly, there would have to be an open gateway for mixing between the deep or

intermediate water directly affected by the eruption and the water at Demerara Rise.

Elemental abundances measured by Orth in the WIS, the Atlantic, and Pacific show large

peaks during OAE2 that are indicative of increased seafloor spreading and hydrothermal

processes. These anomalies are larger in the west and get smaller toward the east

traveling from the Pacific into the Atlantic (1993). This west to east trend possibly

indicates a west to east circulation pattern, thus connecting the eruption site (equatorial

eastern Pacific) with Demerara Rise. The second assumption is that the anoxic

conditions would have prevented the quantitative removal of Nd from hydrothermal vents

sites. In modern oceans Nd is effectively removed at hydrothermal vent sites by Fe-Mn

hydroxides (Michard et al., 1983; German et al., 1990), and is not circulated into the









ocean; however, the situation may have been very different under anoxic deep water

conditions.

The problem with the LIP and increased sea floor production hypothesis is that it

has been established that the basin surrounding Demerara rise was effectively isolated

from other deep water masses (e.g. the one at Blake Nose), thus the eruption had to have

a major effect on the surface water in order for it to affect deep to intermediate waters at

Demerara. Otherwise some other process would have had to be coincident with the

eruption of the LIPS and increase in ocean crust production, such as sea level rise or a

change in upwelling. A greater problem is that there were two pulses of volcanism from

the Caribbean LIP, as recorded in the WIS (Snow et al., 2005). Due to limited correlation

between the WIS and Demerara Rise it is difficult to determine whether the two peaks

seen in the Nd record, at 423.5 and 425.5 mcd, could be an effect of the two volcanic

pulses. The pulses of volcanic activity identified by Erbacher (2004) do not correlate to

peaks in the Nd record. There is also no evidence for a volcanic event associated with the

mid-Cenomanian event for which there are similar shifts in 613C and ENd.

The final hypothesis that could explain the positive excursions in both the 613C and

the SNd values across OAE2 is a change in the upwelling pattern at Demerara Rise.

Upwelling would effectively bring nutrient rich waters from depth causing an increase in

productivity directly leading to a positive excursion in 613Corg and the deposition of black

shales (e.g. Handoh, 2003). Upwelling could also cause increased mixing as the

upwelled water is replaced by intermediate or deep water from a different location, in this

case possibly the more radiogenic waters that bathed Blake Nose and/or the Pacific.

Changes in trace metal abundances in black shales from OAE2 exhibit signatures that are









indicative of coastal upwelling (Brumsack, 2005). It has also been suggested that

volcanic processes may have generated a buoyant plume that initiated upwelling (Vogt,

1989).

Work by Kolonic et al. (2005) supports the theory that wind-driven upwelling is a

mechanism for driving nutrient-rich waters to the surface to increase productivity. His

recent work off the northwest coast of Africa found black shale formations interbedded

with thin layers of carbonate sediment, suggestive of oxic conditions, and attributes these

lithologic changes to the alternating position of the Intertropical Convergence Zone

(ITCZ). Movement of the ITCZ can cause periods of arid conditions when it is located at

a more southerly position, followed by extremely humid conditions, when the

convergence migrates to the north. This atmospheric driven oceanographic change is

supported by modeling experiments across the Cenomanian- Turonian boundary (Flogel,

2002). A modeling experiment of a proposed Tethyan circumglobal current also predicts

seasonal monsoonal events (Bush and Philander, 1997). The modern analogue to this

movement of the ITCZ is seen on the west coast of the African continent. During the

northern hemisphere summer there are strong northerlies, which move the ITCZ north

causing moist air to move inland over the continent. During the northern hemisphere

winter the northerlies are weak, the ITCZ is in its more southern position, and dry air

flows off the continent from the north leading to a more arid climate. When the ITCZ is

in a more southerly position the weaker trades allow for upwelling along the coast. If this

same idea is used on the South American continent there would be little to no upwelling

on the east coast when the ITCZ is in a more northerly position and enhanced upwelling

when it is in a more southerly position. Today, the movement of the ITCZ is a seasonal









change, so it is difficult to use this mechanism to explain a 106 year event. Kolonic

(2005) invokes the idea of an orbital control on the location of the

ITCZ otzrI a ozpovy 100,000 ysEap sXXsvpzptxtz c t yvaL, YszCT QupTrsp zTsC c ouM6

PE vss6 To 7Tpozns TICZlY.

(Duptsp ItvzsCTotyaUCtov It psOutps6 to Xovocpatv Ts XauCos o TrtoIC yopa

k avotix sEsvT, YEST trs 613C and SNd records are undoubtedly linked. Therefore, the

mechanism for anoxia must combine both productivity in the water column as well as

enhanced intermediate to deep water mixing. Significantly, these data argue against the

theory of stagnation as the cause for anoxia.














CHAPTER 7
BACKGROUND ON EXTRACTION EXPERIMENTS

Rutberg et al. (2000) first demonstrated that Nd extracted from extracted Fe-Mn

oxide coatings was an effective tracer for ocean circulation on Pleistocene timescales.

Their Nd isotopic record from a core in Cape Basin confirmed previous ideas that

NADW production decreased during cold marine isotope stages stages 2 and 4 (e.g. Mix

et al., 1985; Oppo and Fairbanks, 1987; Charles et al., 1992). Their procedure designed

to selectively extract the Fe-Mn oxide coatings was modified from Chester and Hughes

(1967) and used buffered acetic acid to remove the carbonate fraction followed by a 0.02

M hydroxylamine hydrochloride (HH) solution to reduce the Fe-Mn oxide fraction.

Using this procedure Piotrowski et al. (2004) developed the record presented above to

track millennial time scale changes in the strength of NADW over the last 20 kyr (figure

2-3).

The procedure used by Rutberg et al. (2000) was further tested by Bayon et al.

(2001) in a study of the Last Glacial Maximum (last 30 kyr) from a different core in the

Cape Basin. This study was designed to isolate the detrital fraction as well as the Fe-Mn

oxide fraction of a marine sediment sample. Both of these fractions were then used to

identify changes in ocean circulation. The continental sources of the detrital fraction

provided information about the provenance of this material and possible water current

directions, while Nd isotopes were extracted from the Fe-Mn oxide fraction. A number

of variations in the technique were developed in order to completely isolate the detrital

and Fe-Mn fractions. These variations included changes to the strength of the HH









solution, heating the sample during extraction, and removing the organic fraction prior to

extraction. In the most effective procedure, an acetic acid wash was used to remove the

carbonate fraction and a 0.5 M HH solution was used to remove the Fe-Mn oxide

fraction, similar to Rutberg et al. (2000); however, they determined that using a HH

solution with a lower molarity (0.04) did not remove the whole of the Fe-Mn oxide

fraction and the Nd isotopic value of the detrital fraction was shifted toward seawater

values. Each variation on the extraction procedure was systematically tested using Sr

isotopes and REE patterns. It was assumed that the Nd isotopes were accurately

recording the value of deep water when the Sr isotopes yielded appropriate seawater

values. REE patterns of the various fractions are distinctly different and were used to

verify whether the Fe-Mn oxide and detrital fraction were effectively separated from one

another. This study was the first to systematically test the acetic acid wash and HH

solution procedure. In conclusion, the detrital fraction could be effectively separated

from the Fe-Mn oxide portion, but it proved very difficult to isolate the oxide portion

with no effect from either the detritus, carbonate or the organic fractions.














CHAPTER 8
RESULTS OF THE FE-MN OXIDE COATING EXTRACTION PROCEDURE AND
VALIDITY TESTS

8.1 Variations on the Extraction Procedure

The main goal of this portion of this project was to determine if it was possible to

obtain Nd isotopic values from Fe-Mn oxide coatings that reflect seawater values on

Cenozoic time scales. Bayon et al. (2000), Rutberg et al. (2000), and Piotrowski et al.

(2004) demonstrated that extraction techniques are effective on younger timescales, but

there is yet to be a systematic study of older sediments. To test the validity of the Nd

isotopic values obtained from the extracted coatings in this study, they were compared to

values from contemporaneous fossil fish teeth, assuming that the Nd isotopic value

obtained from the fish teeth was correct. The extraction procedure by Rutberg et al.

(2000) was the initial procedure used for this study, and it was subsequently modified.

The main concern with any extraction procedure is the removal of material other

than the desired Fe-Mn oxide coating. Contamination from detrital material is likely to

have an effect on the ENd value obtained, altering it toward more or less radiogenic values

depending on the source. Detrital in this case refers to any clay or other terrigenous

material as well as any particulate contamination from volcanic sources or hydrothermal

processes. The first steps taken to minimize detrital contamination were to alter the grain

size used for extraction, the molarity of the HH solution, and the length of the extraction

time.










The first variable tested was the grain size of the sediment. A previous study by

Scher et al. (2003), on samples from ODP Site 1090, determined that extracting coatings

from the <63 |tm size fraction in many cases did not give SNd values that fell within error

of the values obtained from fossil fish teeth (Figure 8-1). The less than 63 |tm fraction is

composed chiefly of clay material, and although the particles may have oxide coatings,

the chances of obtaining seawater values are greater if this possible contaminant can be

eliminated. The 63-125 |tm and >125 |tm size fractions were also tested. A number of

samples from each of those two size fractions were extracted and analyzed. It was

determined that there was no distinguishable difference between samples of 63-125 |tm

and >125 |tm size fraction samples (Figure 8-1). Samples used in the remainder of this

study consist of >63 |jm size fraction of sediment.

















S-631
8 i








>125
-5
Sample Number
Figure 8-1. The difference of SNd between fossil fish and Fe-Mn oxide coatings from
-5 ---------------~



samples of < 63 |tm (circles), 63-125 |tm (squares) and >125 |tm (triangles)
size fractions. Samples with a difference less than 0.5 SNd units are assumed
to agree within error for the TIMS.









The other variable tested was the length of time the HH solution remained on the

sediment. For this test all samples were extracted with a 0.5M HH solution. Work by

Bayon et al. (2001) determined that 1M HH solution removed nearly all the Fe-Mn oxide

coating on marine sediment, leaving the remaining detrital material clean, which was

their targeted material. By using a lower molarity HH solution, enough of the coating

was removed for this study, but there was less chance of contamination from the

remaining detrital material. Although the solution was weaker, an additional test was set

up to determine whether it would have the same effect as the stronger solution if it were

left on the samples for an extended length of time. To test this, sequential sediment

samples were treated for 4, 2, and 1 hour time intervals. As figure 8-2 illustrates, samples

treated for 1-2 hours fell within error of the contemporaneous fossil fish teeth samples

more often than samples treated for 4 hours. Several of the samples that were treated for

4 hours did not give SNd values that were close to the values obtained from the fish teeth.

In these cases the HH solution must have removed nearly all the Fe-Mn oxide coating

and reacted with some of the detrital material, thus altering the isotopic signal towards

more less radiogenic values indicating contamination from a continental source. A

possible source of this contamination might be cations from exchangeable sites on the

clays. As a result, samples used in this study were treated for 1.5- 2 hours with a 0.5 M

HH solution.















0 T



0
iN 2 - - -- --.. .. .


0 -3 -----.. . .
4 -2



4 hours
-5 2 hours
S1 hour
-6
Sample Number
Figure 8-2. Difference of ENd from obtained from fossil fish teeth and samples treated for
4 (diamonds), 2 (squares), and 1 (triangles) hour extraction periods.

8.2 Results from Southern Ocean Sites

Samples of fish teeth and Fe-Mn oxide coatings from 15-40 Ma (Miocene to

Eocene) were analyzed from Sites 689, 690, and 1090 in the Southern Ocean (see figure

2-6 for site locations). The SNd values from fish teeth for Site 689 range from -7.7 to -9.1

and values from Fe-Mn oxide coatings range from -7.7 to -9.7 (table 8-1). Out of 27

samples from Site 689 4 (15%) did not fall within error of the fossil fish teeth (figure 8-

3A); however, all coatings were less radiogenic than the teeth. The ages of samples from

Site 690 range from 26 to 44 Ma (Oligocene to Eocene) with SNd values for teeth ranging

from -8.7 to -10.2 (table 8-1). Values for the coatings range from -8.2 to -10.5 and out of

23 samples 5 (-22%) values from oxide coatings did not fall within error of the fossil fish

teeth (figure 8-3B). All but one of the samples that fell outside of error of the fish teeth

was less radiogenic than the corresponding teeth value. Site 1090 teeth and coating







66


samples range in age from 17-25 Ma (Miocene to Oligocene), ENd values from fossil fish

teeth range from -7 to -8.3 and coating values range from -6.9 to -8.3 (table 8-1). Out of

17 samples all coating samples fell within error of ENd values obtained from fossil fish

teeth (figure 8-3C). Thus, in the Southern Ocean 88% of the ENd values obtained from

Fe-Mn oxide coatings fell within error of the values obtained from the fossil fish teeth.

The greatest discrepancy between the extracted coatings and fish teeth is 1.5 ENd units,

and the average offset is 0.9 ENd units.

689


-10 I I -
-0-- teeth
A Fe-Mn coating A
-10.5
20 24 28 32 36 40
Ma
Figure 8-3 ENd(o) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings (red
triangles) from the Southern Ocean Sites. A-689, B- 690, and C. 1090.
Arrows on the plots for 689 and 690 highlight the Fe-Mn oxide coatings that
did not fall within error of the teeth.







67

690
-7.5
Teeth
A Fe-Mn coatings
-8 -


-8.5


-9


-9.5



-10


-10.5 ---


-11 B

25 30 35 40 45
Ma
1090
-6.5
-teeth
A Fe-Mn coatings

-7




-7.5




-8




-8.5

C

-9
16 18 20 22 24 26
Ma

Figure 8-3 A-C continued.











Table 8-1. Nd isotopic values from Fossil Fish Teeth and Fe-Mn
Southern Ocean ODP Sites 689, 690, and 1090


Sample
689B
6897-618
689 7-6 121
689 8-1 84
689 8-2 83.5
689 8-3 4
689 8-3, 129
689 8-3, 140
689 8-5, 111.5
*689 9-1, 26
689 9-2, 7
*689 9-3, 62.5
*689 9-6, 63
689 10-3, 116.5
68910-526
689 11-2, 46
689 11-5, 106
689 12-2, 7.5
*689 13-1, 127.5
689 13-2 107
68913-482
68913-6,60
689 14-3, 104
689 14-4 82-88
68915-445
689 16-3,46
689 17-7 51-57
68918-2,60
690B
690 7-4,83
690 7-5,87
690 7-6, 34
*690 8-3, 121
690 8-4,67
6908-517
690 8-6, 67
690 9-3, 148
*690 9-5 148
690 10-2, 136
*690 10-3 87
690 10-4, 135
*690 10-5 84
69010-6,35
690 11-1, 18
69011-3, 17
690 11-4, 68
*690 11-5 17


60.590
61.610
63.340
64.840
65.540
66.790
66.900
69.610
72.360
73.670
75.720
80.230
85.865
87.960
93.260
98.360
103.920
111.880
113.170
115.920
118.700
124.240
125.550
134.850
142.860
158.640
160.900

54.205
57.240
58.210
64.280
65.240
66.245
68.240
74.255
77.250
82.230
83.240
85.225
86.215
87.215
89.250
92.250
94.250
95.240


17.91
18.23
18.49
18.69
19.75
20.11
24.79
25.32
25.85
26.11
26.51
27.13
27.91
28.20
28.90
29.51
30.00
32.02
32.30
32.89
33.38
34.71
35.00
36.05
37.24
39.55
40.07

26.03
26.24
26.34
27.44
27.56
27.69
27.94
28.78
29.06
29.72
29.94
30.57
30.95
31.33
32.12
33.27
35.95
36.22


0.51217
0.512239
0.512217
0.512202
0.512157
0.512196
0.512173
0.51219
0.512165
0.512170
0.512171
0.512162
0.512194
0.512186
0.512155
0.512172
0.512183
0.512181
0.512195
0.512170
0.512223
0.51223
0.512204
0.512184
0.51222
0.512165
0.512143

0.512167
0.512163
0.512174
0.512125
0.512142
0.512148
0.512173
0.512103
0.512122
0.51214
0.512106
0.512149
0.512220
0.512154
0.512147
0.512175
0.51219
0.512141


-9.14
-7.78
-8.22
-8.51
-9.38
-8.63
-9.06
-8.74
-9.22
-8.64
-9.10
-9.29
-8.66
-8.82
-9.42
-9.09
-8.88
-8.91 0
-8.64
-9.13
-8.10
-7.95
-8.47
-8.86
-8.16
-9.23
-9.66

-9.19
-9.26
-9.06
-10.01
-9.68
-9.56
-9.08
-10.44
-10.07
-9.72
-10.38
-9.54
-8.15
-9.45
-9.58
-9.03
-8.75
-9.69


0.25
0.34
0.25
0.25
0.70
0.25
0.25
0.25
0.25
0.51
0.25
0.25
0.41
0.45
0.41
0.41
0.41
0.34
0.45
0.45
0.41
0.41
0.45
0.45
0.41
0.45
0.41

0.25
0.25
0.25
0.25
0.34
0.45
0.41
0.41
0.45
0.41
0.45
0.41
0.45
0.41
0.25
0.25
0.41
0.45


Oxide Coatings from


0.512188
0.512213
0.512206
0.512179
0.512198
0.512195
0.512187
0.512187
0.512198
0.512224
0.512219
0.512233
0.512186
0.512221
0.512181
0.512203
0.512201
0.512220
0.512203
0.512202
0.512228
0.512246
0.512227
0.512207
0.512194
0.512192
0.512173

0.512191
0.512189
0.512191
0.512157
0.512156
0.512157
0.512175
0.512131
0.512172
0.512139
0.512149
0.512138
0.512141
0.512151
0.512166
0.512175
0.512185
0.512183


-8.78
-8.29
-8.43
-8.95
-8.58
-8.64
-8.79
-8.79
-8.58
-8.07
-8.17
-7.90
-8.82
-8.14
-8.92
-8.48
-8.52
-8.16
-8.49
-8.51
-7.99
-7.65
-8.02
-8.40
-8.67
-8.70
-9.06

-8.73
-8.77
-8.72
-9.38
-9.41
-9.38
-9.03
-9.88
-9.09
-9.74
-9.53
-9.76
-9.69
-9.49
-9.22
-9.02
-8.84
-8.88


0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.31
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27

0.27
0.27
0.27
0.27
0.27
0.25
0.27
0.27
0.25
0.27
0.25
0.27
0.25
0.27
0.27
0.27
0.27
0.25


Coatings2 Teeth4
mbsf Age (Ma)1 143/144 SNd(o)3 143/144 SNd(o)










Table 8-1. Continued
69011-7,17 98.240 37.11 0.512176 -9.02 0.41 0.512143 -9.65 0.42
690 11-7, 17 rep 98.240 37.11 0.512167 -9.19 0.34 0.512143 -9.65 0.42
690 12-1,146 100.230 37.76 0.51216 -9.33 0.41 0.512151 -9.50 0.27
690 12-3, 146 103.230 38.75 0.512173 -9.07 0.25 0.512183 -8.87 0.27
69012-694 107.210 41.88 0.512107 -10.36 0.45 0.512131 -9.90 0.25
69012-7, 47 108.240 42.83 0.512128 -9.94 0.41 0.512125 -10.01 0.27
69013-3,74 112.210 44.18 0.51211 -10.29 0.41 0.512115 -10.20 0.27
1090
1090D 8-2, 138 73.190 16.31 0.512211 -8.33 0.27 0.512212 -8.31 0.27
1090D 8-3, 48 73.790 16.45 0.512224 -8.08 0.27 0.512220 -8.16 0.27
1090D 8-6, 38 78.190 17.26 0.512242 -7.73 0.27 0.512247 -7.62 0.27
1090E 8-4, 133 80.080 17.49 0.512227 -8.02 0.27 0.512244 -7.69 0.27
1090D 9-2, 5 82.980 17.91 0.512229 -7.98 0.27 0.512231 -7.94 0.27
1090E 9-2, 137 87.980 18.54 0.512246 -7.65 0.27 0.512247 -7.63 0.27
1090E 9-4, 48 90.090 18.75 0.512237 -7.83 0.29 0.512262 -7.34 0.27
1090D 10-3, 5 93.980 19.21 0.512218 -8.20 0.29 0.512247 -7.63 0.27
1090D 10-4,35 95.780 19.39 0.512250 -7.58 0.29 0.512254 -7.49 0.27
1090E 10-4, 36 99.930 19.80 0.512242 -7.72 0.29 0.512239 -7.79 0.27
1090D 11-3, 90 103.930 20.20 0.512265 -7.27 0.29 0.512265 -7.28 0.27
1090E 11-3, 122 108.230 20.61 0.512278 -7.03 0.29 0.512273 -7.12 0.27
1090D 12-2, 130 112.330 21.00 0.512286 -6.86 0.29 0.512278 -7.02 0.27
1090D 13-4, 39 123.680 22.45 0.512215 -8.26 0.29 0.512223 -8.09 0.27
1090E 13-3, 8 125.890 22.66 0.512213 -8.30 0.29 0.512221 -8.13 0.27
1090E 16-5, 116 160.920 24.88 0.512254 -7.50 0.29 0.512239 -7.78 0.27
1090D 17-3, 34 163.120 25.08 0.512258 -7.42 0.29 0.512258 -7.40 0.27
1 Ages for Site 689 from Mead and Hodell, 1995; Spiess, 1990; Shipboard Scientific Party, 1988.
Ages for Site 690, Shipboard Scientific Party, 1988; and for Site 1090 are from Scher, 2006.
2143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and
then normalized to Jndi-1 = 0.512103 (TIMS average).
3 Fossil fish teeth data from Scher, 2005.
4. ENd(o) = [(43Nd/ 44Nd)sample Nd/ 44Nd)CHUR-1] X 104
* indicates samples whose coating and teeth were not within error of one another.

8.3 Results from North Atlantic Sites

Fish teeth samples and extracted coatings from contemporaneous sections were

analyzed from North Atlantic DSDP Site 608 and ODP Sites 647 and 982. Due to the

scarcity of teeth in samples from Site 608 only 2 samples were analyzed. The SNd values

of the teeth from these two samples are -11.07 and -12.30. Coatings for both of these

samples fall outside the error window at -9.66 and -11.28 respectively (table 8-2 and

figure 8-4). Four samples were analyzed from Site 647 and SNd values of the teeth range

from -9.93 to -11.61, while Fe-Mn oxide coating values range from -9.66 to -11.28 (table










8-2). All four of these samples fell within error of the contemporaneous fish teeth (figure

8-4). For all of the samples analyzed from these two sites the coating samples were

consistently more radiogenic than the fish teeth samples.


-9.5
608 coating
608 teeth
-10 A 647 coating
A 647 teeth

-10.5 ..


? ~ ~ ~~~~ ---11-- ^- ,^ ^ ^- ^ ^ ^ -^ ^ -^ ^ -
S- -11


-11.5


1 2 - -' '-' -


-12.5
5.5 6 6.5 7 7.5 8 8.5 9 31.5 31

Ma
Figure 8-4 SNd(o) values from fossil fish teeth and Fe-Mn oxide coatings from DSDP Site
608 (circles) and ODP Site 647 (triangles) from 5.5 to 9 and from 30 to 31
Ma.

Twelve samples were analyzed from ODP Site 982 spanning from 9.2 to 14.4 Ma.

Fossil fish teeth as well as phosphate pieces or fish debris (commonly bones or scales)

were analyzed for three of the samples. The SNd values obtained from the two types of

phosphates are indistinguishable, implying that when fish teeth are absent from a sample,

phosphate fish debris can be used instead (table 8-2). The SNd values from the fish teeth

and debris range from -8.13 to -10.86, and the oxide coating values range from -8.66 to -

10.61, with all of the values falling within error of the teeth (table 9-2). In these samples

the coating values are not consistently more or less radiogenic than the teeth (figure 8-5).







71


Of all the samples analyzed in the North Atlantic (all 3 localities) 88% of the values

obtained from coating samples agreed with the values obtained for the teeth.


982
-7.5
A Fe-Mn coating
-8 teeth


-8.5


-9--- --- -- ----- --- --- --- ---


9 10 11 12 13 14
Ma

Figure 8-5. SNd(o) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings
(red triangles) from ODP Site 982 from 9 to 15 Ma.










Table 8-2. Nd isotopic values from Fossil Fish Teeth and Fe-Mn Oxide Coatings from
North Atlantic DSDP and ODP Sites 608, 647, and 982
Coatings Teeth
Sample mbsf Age (Ma)3 1431144Nd sNd(o)5 1431144Nd ENd(o)
608
*608 17-1, 102.5 152.000 5.77 0.51206 -11.28 0.38 0.512008 -12.30 0.55
*60820-2, 10.5 177.300 7.20 0.512143 -9.659 0.38 0.512070 -11.07 0.27
647
647 13-1, 104 117.010 7.70 0.512079 -10.9 0.38 0.512049 -11.48 0.27
64713-1,133 117.300 7.94 0.512048 -11.5 0.38 0.512043 -11.61 0.31
647 13-2, 34.5 117.815 8.36 0.512063 -11.21 0.38 0.512044 -11.59 0.27
64717-1,62 155.390 30.40 0.512132 -9.864 0.38 0.512129 -9.93 0.27
982
982 34-1 52.5A1 307.150 9.21 0.512105 -10.40 0.45 0.512128 -9.95 0.45
982 34-1 52.5B2 307.155 9.21 0.512105 -10.40 0.45 0.512110 -10.30 0.45
982 36-1 12 326.310 9.77 0.512118 -10.14 0.45 0.512146 -9.60 0.45
982 39-5 22.5A 355.825 10.63 0.512094 -10.61 0.45 0.512081 -10.87 0.45
982 39-5 22.5B 355.825 10.63 0.512094 -10.61 0.45 0.512101 -10.48 0.45
982 41-5 5.5B 375.103 11.20 0.512110 -10.30 0.45 0.512126 -9.99 0.45
982 43-3 103.5A 394.205 12.14 0.512187 -8.80 0.45 0.512206 -8.43 0.45
982 45-2 27.5B 413.175 12.64 0.512194 -8.66 0.45 0.512221 -8.13 0.45
982 47-1 62B 432.260 13.13 0.512130 -9.91 0.45 0.512118 -10.14 0.45
982 51-1 17.5A 470.615 14.13 0.512103 -10.44 0.45 0.512089 -10.71 0.45
982 51-1 1 spiked 470.615 14.13 0.512103 -10.44 0.45 0.512102 -10.46 0.45
982 52-4 2 spiked 480.675 14.40 0.512143 -9.66 0.45 0.512112 -10.26 0.45
1A samples are values from fossil fish teeth
2B samples are values from phosphate pieces, commonly fish debris such as scales or bone.
3 Ages for Site 608 are from Ruddiman et al., 1987; for Site 647 Shipboard Scientific Party, 1987;
and for 982 Shipboard Scientific Party, 1996.
4 143/144Nd values are normalized to the Jndi-1 average on the day the samples were analyzed and
then normalized to Jndi-1 = 0.512103 (TIMS average)
5.Nd(o) = [(43Nd/ 44Nd)saple/ Nd/ 44Nd)CHUR-] X 104
* indicates samples whose coating and teeth values were not within error of one another.

8.4 Results from Cretaceous Samples

As one final test, this extraction procedure was performed on four samples from

Cretaceous sediments (80-102 Ma) from ODP Sites 1050 and 1258. The SNd value for the

fish teeth from the one sample from Site 1258 was -15.44 and the value from the coating

was -16.05. From Site 1050 fish teeth values range from -5.00 to -8.44 and coating

values range from -5.56 to -8.93 (table 8-3). The coating values of all four samples fell

within error of the values obtained from the fish teeth and are not consistently more or


less radiogenic than the teeth values (Figure 8-6).

















-8



J -10


-12


-14
0 teeth
A Fe-Mn coatings
-16
75 80 85 90 95 100 105
Ma
Figure 8-6. SNd(t) values from fossil fish teeth (blue circles) and Fe-Mn oxide coatings
(red triangles) from ODP Sites 1258 and 1090 from 77 to 102 Ma.

Table 8-3. Nd istopes from Fossil Fish Teeth and Fe-Mn Oxide Coatings from ODP Sites
1258 and 1050.
Teeth2 Coatings
Sample mcd Age (Ma)1 1431144Nd Nd(o)3 Nd(t)4 143144Nd sNd(o) SNd(t)
1258 38-1 105 375.20 80.00 0.511804 -16.27 -15.44 0.25 0.511815 -16.05 -15.22 0.45
1050 20-1 33 490.63 77.00 0.512179 -8.95 -8.44 0.25 0.512180 -8.93 -8.42 0.45
1050 29-2 102 577.46 99.73 0.512334 -5.93 -5.06 0.25 0.512353 -5.56 -4.69 0.45
1050 31-2 103 596.65 101.30 0.512337 -5.87 -5.00 0.25 0.512314 -6.32 -5.45 0.45
1 Ages for Site 1258 are from Erbacher, 2004 and for Site 1050 from Shipboard Scientific Party, 1998.
2 143/144Nd values are normalized to Jndi-1 average on the day the samples were analyzed and
then normalized to Jndi-1 = 0.512103 (TIMS average).
3. ENd(o) [(43 Nd/ 44Nd)sample/ 43Nd/ 44Nd)CHUR-1] X 104
4. ENd(t) 143Nd/144Nd)sample(t)14Nd Nd)CHUR(t)-l] X 104 using 14Sm/144Nd

8.5 Tests of Validity

Although a majority -90% of the extracted Fe-Mn oxide coatings do fall within error

of the contemporaneous fossil fish teeth, some do not and the scope of the next portion of

the project was to determine whether there is a test other than analyzing fish teeth that

could be used to identify coating samples with accurate SNd values. If successful, the goal










was that these tests could be used in place of the more time consuming, complicated and

expensive analyses of fossil fish teeth. Tests for the integrity of the coatings include REE

plots, Sr isotopes, and major element ratios, which were all expected to detect possible

contamination.

8.5.1 REE Plots

REE plots for different geological materials are very distinct; continental material,

basalts, fish teeth, and Fe-Mn oxide coatings all produce unique REE profiles. The goal

was to determine whether the REE patterns for extracted coating samples that did not

match the SNd value of the fossil fish teeth were distinct from those that did agree with the

teeth data.

10
10 '------- ----- ----------- ---- --'---'---'








01
E
-- -- ----| ^ <- <>-- -- < ---- -- - -- - -

N

0.1
0
z



S---o si de of error
S-*-within error
0.01
La Ce Pr Nd Sm Eu Gb Tb Ho Yb Lu

Figure 8-7. REE plot of four samples from ODP Site 690, two of the samples have SNd
values that fall within error of contemporaneous fossil fish teeth (green
triangles) and two do not (red circles). Samples are normalized to the initial
sample weight and to PAAS (Taylor and McLellen, 1985).









All of the REE plots from Fe-Mn oxide coatings for this study have a distinctive middle

(M-) REE buldge, characterized by enrichment in the MREE and a depletion in the light

(L-) REE and heavy (H-) REE. This is consistent with analysis of REE from Fe-Mn

oxide coatings from other studies (e.g. Bayon, 2002). To determine if REE patterns are

different for extracted samples that fell within error of the fish teeth and those that did

not, four samples were plotted from Site 690; two whose ENd values fell within error of

the teeth and two that did not (figure 8-7). Both sets of samples have similar REE

patterns, including MREE enrichment, characteristic of Fe-Mn oxide coatings. There is,

however, slight variability in the magnitude of the Ce anomalies.

REE were analyzed from extracted coatings from all locations in this study,

including the samples from the Cretaceous (table 8-4). The samples from each Site were

averaged to get a REE pattern for each location. These results are plotted on figure 8-8.

All the Sites have a MREE bulge and variable negative Ce anomalies. All samples have

been normalized to the original sample weight as well as PAAS and, therefore, they do

reflect relative concentrations. Samples from Site 690 and 689 in the Southern Ocean

have the highest concentration, while the North Atlantic samples have lower

concentrations of REE. In particular, concentrations from Site 608 are about an order of

magnitude lower than all other sites. The 4 samples analyzed from Cretaceous sediments

from Sites 1050 and 1258 have concentrations that fall between the Southern Ocean and

North Atlantic.










-- -647
A 608
- 982
-Cretaceous
-* 1090
- 690
-- 689


La Ce Pr Nd Sm Eu Gb Tb Ho Yb Lu


.REE plot of the average
Atlantic Sites 608 (triangle)
(Sites 1258 and 1050; (bo:
(diamond), 690 (cross) and
(Taylor and McLellen, 1985


values from extracted coatings from the North
), 647 (circle), and 982 (square), the Cretaceous
x with x), and the Southern Ocean Sites 1090
689 (triangle). REE are normalized to PAAS
) and initial sample weights.


0.01




0.001


Figure 8-8










Table 8-4 REE values from Fe-Mn


Sample
North Atlantic
608
608 17-1 102.5
647
647 3-1 104
647 13-2,34.5
982
982 34-1 52.5
982 36-1 9
982 41-5 3-8
982 43-3 103.5
982 45-2 28
982 47-1 162
982 51-1 17.5
982 52-4 27.5
Average NA
Southern Ocean
689
689 10-3 86.5
689 10-5 26
689 13-1 127.5
689 13-2 104
689 13-482
689 13-6 60
689 14-485
689 15-4 45
689 16-346
689 17-6 61
689 17-754
689 18-2 60
Average 689
690
690 8-4 66
690 8-5 14
690 9-3 148
690 9-5 147.5
690 10-584
690 11-5 16.5
690 11-717
690 11-7 17rep
690 12-694
690 12-747
690 13-3 24
Average 690
1090
1090 12-5 112.5
Error is 5%.


La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu


0.017 0.005 0.016 0.017 0.019 0.022 0.024 0.023 0.021 0.016 0.014

0.063 0.105 0.129 0.161 0.267 0.317 0.325 0.303 0.226 0.160 0.145
0.038 0.070 0.080 0.101 0.171 0.200 0.199 0.180 0.132 0.096 0.088


0.216
0.035
0.057
0.180
0.053
0.031
0.334
0.183
0.101


1.162
1.125
0.466
0.404
0.264
0.438
0.964
0.786
0.352
0.401
0.748
0.253
0.571

0.702
1.088
0.101
1.355
0.835
1.529
0.021
0.235
0.400
0.108
0.029
0.582


0.082
0.020
0.030
0.078
0.032
0.015
0.188
0.089
0.060


0.478
0.331
0.138
0.157
0.073
0.086
0.375
0.320
0.079
0.137
0.285
0.082
0.195

0.217
0.372
0.039
0.770
0.625
0.908
0.008
0.050
0.406
0.066
0.021
0.316


0.250
0.064
0.094
0.205
0.084
0.048
0.401
0.190
0.132


1.257
1.374
0.471
0.493
0.364
0.375
1.074
0.940
0.239
0.283
0.863
0.142
0.613

1.035
1.272
0.147
1.721
1.108
1.812
0.023
0.326
0.643
0.175
0.036
0.754


0.330
0.083
0.127
0.273
0.111
0.057
0.511
0.239
0.170


1.657
1.853
0.487
0.624
0.491
0.374
1.400
1.246
0.216
0.269
1.156
0.120
0.768

1.111
1.604
0.165
2.224
1.380
2.488
0.026
0.365
0.880
0.195
0.040
0.953


0.411
0.131
0.195
0.354
0.172
0.088
0.628
0.293
0.231


2.059
2.324
0.584
0.793
0.648
0.424
1.700
1.553
0.218
0.284
1.415
0.107
0.940

1.450
1.971
0.217
2.743
1.814
3.038
0.031
0.469
1.243
0.272
0.049
1.209


0.471
0.140
0.216
0.413
0.184
0.099
0.703
0.322
0.260


2.202
2.580
0.651
0.886
0.733
0.491
1.953
1.756
0.249
0.334
1.614
0.127
1.056

1.483
2.080
0.230
2.984
1.930
3.494
0.034
0.505
1.394
0.307
0.053
1.318


0.555
0.154
0.236
0.481
0.204
0.104
0.818
0.394
0.295


2.692
3.022
0.652
1.015
0.847
0.446
2.260
2.016
0.228
0.290
1.869
0.105
1.197

1.672
2.422
0.258
3.346
2.165
3.950
0.041
0.497
1.483
0.256
0.062
1.468


0.508
0.120
0.192
0.435
0.165
0.075
0.712
0.347
0.256


2.557
2.777
0.708
0.998
0.774
0.554
2.175
1.905
0.277
0.358
1.730
0.127
1.158

1.640
2.364
0.241
3.060
2.173
3.426
0.036
0.496
1.392
0.262
0.057
1.377


0.446
0.100
0.156
0.397
0.150
0.078
0.622
0.348
0.225


2.415
2.376
0.697
0.910
0.659
0.612
1.979
1.668
0.332
0.451
1.536
0.195
1.072

1.382
2.097
0.209
2.538
1.833
2.825
0.034
0.403
1.112
0.191
0.052
1.153


0.324
0.080
0.118
0.315
0.134
0.075
0.487
0.301
0.178


2.174
1.673
0.713
0.810
0.480
0.661
1.597
1.237
0.413
0.556
1.118
0.289
0.909

1.240
1.857
0.171
1.906
1.758
1.783
0.025
0.268
0.845
0.127
0.035
0.911


0.268
0.028
0.078
0.270
0.084
0.023
0.409
0.252
0.135


2.345
1.696
0.647
0.766
0.455
0.600
1.607
1.240
0.367
0.526
1.117
0.273
0.902

1.091
1.923
0.156
1.909
1.834
1.825
0.023
0.222
0.804
0.099
0.031
0.901


0.205 0.128 0.267 0.251 0.312 0.318 0.388 0.359 0.306 0.346 0.300


Oxide Coatings.









8.5.2 Strontium Isotopes

Strontium has a long residence time in the ocean, thus the Sr isotopic value of the

ocean is homogeneous at any one time in earth's history. The assumption is that if the

coatings incorporate the ocean water chemistry of the overlying water mass the coating

should incorporate the Sr isotopic value as well as the Nd isotopic value of the water

mass at that time. Other studies that utilized Fe-Mn oxide coatings as archives for Nd,

such as Piotrowski et al. (2004), used Sr isotopes as a tool for evaluating the integrity of

the measured SNd value.

Sr isotopes were measured on a number of the extracted coatings in this study

(table 8-5). These values were compared to 7Sr/86Sr values obtained from foraminifera

from the same sediment sample, which are assumed to represent the seawater value.

Because seawater sSr/86Sr changes with age, the samples have been plotted on the

seawater Sr isotope curve (figure 8-9). They have been divided into two groups;

extracted coatings whose SNd values fell within error of the SNd value of the teeth and

those that did not. All of the samples either fell on the Sr curve or were more radiogenic

than the curve.

There is some correlation between sample locations and Sr isotopic values. All of

the samples from the North Atlantic lie on the curve, while the Southern Ocean samples

are mixed. The North Atlantic samples are also younger than the Southern Ocean

samples, -10-13 Ma and younger versus 19.5 Ma and older. There is, however, no

correlation between the ages of the Southern Ocean samples that fell on and off the curve.

Interestingly a replicate sample (37.0 Ma) yielded two very different Sr isotopic values,












one fell on the Sr curve and one did not even though the Nd isotopic values for the both


coatings were valid.


- - -- -

..
- - - -

-




- - --
1.V
+


error +
error -
leachate within error of teeth
leachate outside of error of teeth


0.7092



0.709



0.7088



0.7086

C)
C 0.7084

0.7082
0.7082


Figure 8-9. Seawater Sr curve over the past 50 Ma (Woodruff and Hodell, 1994; Mead
and Hodell, 1995; Farrell et al., 1995; Martin et al., 1999) plotted with
87Sr/86Sr values from extracted Fe-Mn oxide coatings. Green triangles are
from extracted coatings whose SNd value fell within error of the values
measured from fossil fish teeth and the red boxes are from extracted coatings
whose values fell outside of error of those obtained from the teeth. The
87Sr/86Sr error bars are smaller than the symbols.


. v
^ --- "*.--'f ------------ -- -
A
".' ..


0.708



0.7078



0.7076







80


Table 8-5. 7Sr/86Sr values from Extracted Material and Foraminifera from Samples from
ODP Sites 689, 690, 982, and 1090
Coatings Foraminifera
Sample Age (Ma) 87/86Sr 2 87/86Sr 3


ENd within error of t
689 8-3 129
689 8-3, 4
689 10-526
689 13-2 107.5
689 13-482
689 14-485
689 15-445
689 17-754
690 8-4, 66.5
6908-5 17
690 9-3, 148
690 11-1, 17.5
690 11-7, 17
690 11-7, 17 rep
690 12-694
690 12-7, 47
982 34-1 52.5
982 36-1 12
982 39-5 22.5
982 41-5 5.5
982 45-2 27.5
1090 12-3, 70
ENd outside of error
689 13-1, 124.5
690 9-5 147.5
69010-584
690 11-5 16.5
1 Ages for 689 from


eeth
20.11
19.75
28.20
31.00
32.89
35.00
36.05
39.79
27.56
27.69
28.78
32.12
37.11
37.11
41.88
42.83
10.80
10.05
11.38
11.44
13.32
21.51
of teeth
32.02
29.06
30.95
36.22


0.708371
0.708450
0.708133
0.707940
0.707895
0.707794
0.707772
0.707773
0.708537
0.708259
0.708263
0.708235
0.707824
0.707688
0.707971
0.707914
0.708864
0.708847
0.708813
0.708802
0.708780
0.708323

0.708011
0.708160
0.708103
0.708194


0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023

0.000023
0.000023
0.000023
0.000023


Mead and Hodell, 1995; Spiess, 1990;


0.708425
0.708470
0.708045
0.707960
0.707855
0.707740
0.707760
0.707725
0.708075
0.708033
0.708009
0.707886
0.707735
0.707735
0.707770
0.707831
0.708855
0.708875
0.708840
0.708835
0.708785
0.708354


0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023
0.000023


0.707920 0.000023
0.708005 0.000023
0.707899 0.000023
0.707724 0.000023
Shipboard Scientific


Party, 1988. Ages for 690 from Shipboard Scientific Party, 1988. Ages for 982
from Shipboard Scientific Party, 1996. Ages for 1090 from Scher, 2006
2 Measured 8Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (2o).
and normalized to 86Sr/8Sr = 0.1194.
3 Sr values from 689, 690, and 1090 from Scher et al., 2005.

8.5.3 Major Element Ratios

When SNd values of the coating do not match with fossil fish teeth values, the

assumption is that the fish teeth value is correct and the value obtained from the extracted

Fe-Mn oxide coating has been contaminated by detrital Nd. The source of this Nd is

most likely clay or terrigenous material that has a non-seawater SNd value. To further test









this theory major element ratios were measured on a number of the extracted samples.

Al, Na, K, and Ti, some of the common elements in clays, were ratioed against Fe plus

Mn, the main elements in coatings. Iron and Mn were added together to account for the

high variability seen in the concentrations between the two elements at various locations.

The assumption was that for samples with distinct extracted coating and fish teeth SNd

values the elemental ratios might reflect an increase in the elements contributed from the

clays. Elemental ratios were analyzed for 44 samples from Southern Ocean, North

Atlantic, and the Cretaceous Sites. For 7 of these samples the SNd values of the teeth and

coatings did not match (table 8-6). Ti/(Fe+Mn) ratios range from 0.001 to 0.036 and

there is no discernable correlation between ratios for extracted coatings whose values fell

within error of the teeth and those that did not; in fact the highest values correlate to

samples with matching coating and fish teeth values, while samples with distinct coating

and fish teeth Nd isotopic values record some of the lowest Ti/(Fe+Mn) values (figure 8-

10). This lack of correlation is also seen in the other major element ratios; Mg/(Fe+Mn),

Al/(Fe+Mn) and K/(Fe+Mn).











1.5


0.5 ^-4------------------------------------







-05 647 within

S64789 within
690 within
-1 -X ---------- ---------






-1 ---- ---- --- 982 within
1090 within
SCret. within
-1.5 ----- ---X608 outside
689 outside
690 outside
-2







689 and 690 the red symbols represent those samples whose iNd values for the
Ti/(Fe+Mn)



and the Cretaceous samples from Sites 1050 and 1258. For Sites 608, 647,



teeth and the coatings did not match, while blue symbols throughout represent
samples whose SNd values for the teeth and the coatings did match.










Table 8-6. Maior Element Rations from Site 608, 647, 690, 1090, and 1258


Samples AI/Fe+Mn Mg/Fe+Mn Ti/Fe+Mn Na/Fe+Mn K/Fe+Mn


647 13-1 104
647 13-235
689 8-1 84
689 8-3 4
689 8-3 140
689 10-526
689 13-2 108
689 13-482
689 13-660
689 14-485
68915-445
689 16-346
68917-754
68918-260
690 8-4 66
6908-517
690 9-3 148
69011-717
690 11-7 17 rep
690 12-747
69013-374
982 34-1 53
982 36-1 12
982 39-5 23
982 43-3 104
982 45-2 28
982 47-1 162
982 41-5 5.5
982 51-1 17.5
982 52-4 27.5
1090 13-1 25
109031-434
1050 20-1 33
1050 29-2 102
1050 31-2 103
1258 38-1 105
*608 17-1 103
*689 9-1 26
*689 9-6 63
*689 13-1 128
*690 9-5 148
*690 10-3 87
*690 10-5 84
*690 11-5 17


1.167
1.154
1.117
1.345
0.730
0.089
1.858
2.443
0.512
10.020
6.964
0.210
1.208
0.035
0.063
0.064
0.051
0.178
0.067
1.556
0.534
0.260
0.380
0.918
0.324
0.425
0.525
0.680
0.252
0.511
1.419
1.206
1.601
0.036
0.013
0.472
0.089
1.806
3.630
0.790
0.016
0.030
0.082
0.009


0.497
0.558
0.189
0.133
0.270
0.046
0.468
0.789
2.884
0.694
1.578
2.634
1.120
2.393
0.062
0.057
0.050
0.554
0.100
0.599
2.312
0.128
0.162
0.456
0.063
0.128
0.252
0.155
0.036
0.163
0.356
0.689
0.483
0.041
0.013
0.365
0.422
0.176
0.109
3.939
0.032
0.053
0.059
0.045


0.002
0.001
0.003
0.001
0.001
0.002
0.122
0.064
0.002
0.238
0.004
0.002
0.013
0.001
0.000
0.001
0.000
0.009
0.012
0.036
0.016
0.019
0.004
0.009
0.004
0.002
0.006
0.002
0.016
0.024
0.001
0.001
0.006
0.000
0.000
0.002
0.001
0.002
0.002
0.006
0.001
0.002
0.001
0.001


2.376
7.158
1.765
2.883
4.035
12.971
1381.950
835.928
5.186
3783.426
1104.572
3.583
678.624
3.407
0.142
15.192
0.128
0.684
0.774
5.113
5.614
14.846
1.277
6.711
2.229
1.670
1.730
2.100
5.079
31.595
3.120
4.233
61.866
0.200
0.078
7.421
5.467
2.954
6.087
5.389
2.921
10.806
20.321
2.600


0.851
0.829
0.319
0.510
0.197
0.026
1.113
1.283
0.310
7.001
1.031
0.095
0.573
0.164
0.016
0.021
0.026
0.070
0.058
0.665
0.259
0.121
0.068
0.282
0.113
0.067
0.151
0.136
0.091
0.519
0.404
0.488
1.372
0.013
0.023
0.162
0.081
0.597
0.729
0.412
0.016
0.019
0.024
0.009


SNd teeth-
SNd coating
-0.58
-0.37
-0.21
0.79
0.27
0.67
0.15
0.62
-0.06
0.44
0.45
-0.51
0.53
0.60
0.28
0.18
0.55
-0.64
-0.47
-0.07
0.09
0.45
0.55
0.14
0.37
0.53
-0.23
0.31
-0.27
-0.60
0.28
0.14
-0.02
-0.37
0.45
-0.22
-1.02
0.64
1.39
0.76
0.98
0.84
-1.54
0.82


* indicates that teeth and coatings values do not fall within error of one another.









8.5.4 Sequential Extraction Procedure Results

As a final test for the extracted coatings a sequential extraction and dissolution

procedure was performed. The method for extraction (Bayon et al., 2002) was slightly

different than the extraction method for the single extracted samples. The purpose of this

sequential extraction experiment was to determine the Sr and Nd isotopic values, the Nd

concentrations, and the REE patterns for the various fractions of a given sample including

the carbonate, Fe-Mn oxide coating, and residual fractions.

Using this extraction technique the gNd value of the Fe-Mn oxide coatings

consistently fell within error of the value for the fossil fish teeth (figure 8-11) even for the

samples from Site 608, which previously yielded coatings with values that were too

radiogenic. The SNd value from the carbonate fraction falls within error of the teeth and

coatings for 5 out of the 8 samples, and is not consistently more or less radiogenic for

those samples that fall outside of error. The gNd value from the residual fraction does not

fall within error of the fish teeth for 6 out of the 8 samples, and they are consistently less

radiogenic (table 8-7).

Sr isotopes were also measured from the three separate sediment fractions from the

sequential extractions (table 8-8). The carbonate fraction values fall within error of the

seawater value for six out of the seven samples. For sample 647, 13-4 the carbonate

value is less radiogenic than seawater by 0.000455 (figure 8-11B). The Fe-Mn oxide

coating values either fall within error or are more radiogenic than the seawater value.

The residual fractions for five of six samples are more radiogenic than seawater values.

For 982 47-1 all four fractions yield the same 87Sr/86Sr value.














. .. .. -- ... .. .. ... .. .. .. -- - - -- - --- -r-- .. ... 9
-90






-12

-- ------ --- --- --- --- --- ---13

S* teeth
.----..- ..... --- -- ----- ...... A carbonate -14
: Fe-Mn oxide
Residual
I I 15
---..................---- -- |--- -- | .... -12





0.722 ------------ seawater
A carbonate
a Fe-Mn oxide
0.72 -------------------------------- residual

0.718 -- --------- --- --------- -- ----- --- -- --

S0.716 --

0.714 ---- -------------------

0.712 ----- -------------

0.71 ----- --- ----- -----

0.708 ---- --- --- --- ----- --- --- --- -- --------- -

608 647 689 689 690 690 982 982
21-5 13-4 13-2 15-4 10-5 9-5 34-1 47-1


Figure 8-11. SNd(o) and 87Sr/86Sr values from 8 sequential extraction samples A) SNd(o)
values from 8 sequential extraction samples. Sample 690, 9-5 does not have
an SNd(o) value for the carbonate. B) 8Sr/86Sr values from 8 sequential
extraction samples, errors are smaller than the data points. Each sample
represents 4-5 cm from the core sample indicated. Sample 690, 9-5 does not
have an 87Sr/86Sr value for the carbonate fraction and samples 608, 21-5; 689,
13-2; 689, 154; and 690, 9-5 do not have values for the residual fraction.
Seawater values from Hodell and Woodruff, 1994; Farrell et al., 1995; Mead
and Hodell, 1995; Martin et al., 1999.










Table 8-7. 143/144Nd values for Fossil Fish Teeth, Carbonate, Fe-Mn Oxide Coatings,
and Residual Fractions from the Sequential Extraction Samples
Teeth1 Carbonate Fe-Mn Oxide Residual
14,1/144 M 2N 14,1/144 M 14,/144 14,1144
SNd SNd(o)2 1414 Nd SNd(o) 1 Nd SNd(o) Nd SNd(o)
60821-5 0.512585 -10.28 0.32 0.512090 -10.69 0.45 0.512097 -10.55 0.32 0.512070 -11.08 0.32
647 13-4 0.512583 -10.79 0.32 0.512055 -11.37 0.45 0.512117 -10.16 0.32 0.511921 -13.99 0.32
689 13-2 0.512594 -8.49 0.27 0.512176 -9.01 0.45 0.512199 -8.56 0.32 0.511936 -13.69 0.32
689 15-4 0.512595 -8.40 0.27 0.512214 -8.27 0.45 0.512190 -8.74 0.32 0.512162 -9.29 0.32
690 10-5 0.512588 -9.69 0.27 0.512015 -12.15 0.45 0.512122 -10.07 0.32 0.511948 -13.46 0.32
690 9-5 0.512591 -9.09 0.27 0.512144 -9.64 0.32 0.512031 -11.84 0.32
982 34-1 0.512585 -10.30 0.45 0.512128 -9.95 0.45 0.512108 -10.34 0.32 0.512016 -12.13 0.32
98247-1 0.512586 -10.14 0.45 0.512090 -10.69 0.45 0.512122 -10.07 0.32 0.512111 -10.28 0.32
1Measured 143Nd144Nd of the Jndi-1 standard = .512102 0.000014 (20).
2. ENd(o) [(143Nd/144Nd)sample/(14Nd144Nd)HUR-1] X 104
Table 8-8. 87Sr/86Sr Values for Seawater, Carbonate, Fe-Mn Oxide Coatings, and
Residual Fractions from the Sequential Extraction Samples
Seawater Carbonate' Fe-Mn Oxide Residual
87Sr/86 Sr 87Sr/86 Sr 87Sr/86 Sr 87Sr/86 Sr
608 21-5 0.708920 4.6E-05 0.708954 0.000023 0.708915 0.000023
64713-4 0.708855 4.6E-05 0.708400 0.000023 0.708686 0.000023 0.722691 0.000023
68913-2 0.707905 4.6E-05 0.707874 0.000023 0.708323 0.000023
68915-4 0.707760 4.6E-05 0.707737 0.000029 0.707876 0.000023
69010-5 0.707970 4.6E-05 0.707938 0.000023 0.708404 0.000023 0.718267 0.000023
690 9-5 0.708035 4.6E-05 0.708360 0.000023
982 34-1 0.708790 4.6E-05 0.708919 0.000023 0.708922 0.000023 0.718259 0.000023
982 47-1 0.708875 4.6E-05 0.708809 0.000023 0.708906 0.000023 0.708822 0.000023
1 Measured 87Sr/86Sr of the NBS-987 standard = 0.7120250 0.000023 (20).

REE patterns from the three sediment fractions were also analyzed from each of

the extracted samples (table 8-9). Below are the plots for these REE patterns grouped by

site (figure 8-12, A-D). In all cases the concentration of the residual fraction is an order

of magnitude or more greater than the oxide coating fraction and the carbonate fraction

(figures 8-13A-C). The residual fraction from all samples except for 647, 13-4 and 982,

34-1 have patterns similar to those of the coatings, having a MREE bulge. In contrast,

sample 647, 13-4 is LREE enriched and sample 982, 34-1 has a very flat pattern similar

to that of shale. Interestingly, both 689 samples and 690, 19-6 have a large Eu anomaly.

The anomaly is also seen in the carbonate fraction of these samples. The REE patterns

for all of the oxide coatings have the distinctive MREE bulge indicative of Fe-Mn oxide

coatings and, except for sample 647, 13-4, all of the coating samples exhibit a Ce

depletion. The carbonate fraction in all cases has the lowest concentrations (figure 8-13








87



A-C). The carbonate fraction patterns for samples from 689, 690, and 982 all have


patterns that are similar to the seawater REE pattern, while the carbonate patterns from


both Sites 608 and 647 have a slight MREE bulge.


10 k-


-*-- 608 21-3 res
A- 608 21-3 ox
S i AV 608 21-3 carb
S647 13-4 res
647 13-4 ox
647 13-4 carb
seawater


0.001


La Ce Pr Nd Sm Eu Gd


Tb Ho Yb Lu


- 689 13-2 res
I L- 689 13-2 ox
AV i689 13-2 carb
S689 15-4 res
kA 689 15-4 ox
689 15-4 carb
Seawater


La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu


,)

0. 1
Q.
E
S0.1
0a
a)
N
o
c
0.01





0.001







88


10









) 0.1


o 690 9-5 res
0
JkA A ,690 9-5 ox
0.01 690 9-5 carb
-4-690 10-5 res
690 10-5 ox








A 982 34-1 ox
982 34-1 carb
S982 69010-5 carb
seawater seawater






-0.001------ --






0.001
La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu














Figure 8-12 REE patterns from 8 sequential extractions. (A) Sites 608 and 647, (B) 689,
982 34-1 res
-- 982 34-1 ox
982 34-1 carb












(C) 690, and (D) 982 for 3 different sediment fractions; the residue (res), the
982 47-1 ox : D











Fe-Mn 982 47-1oxide coating (ox) and the carbonate (carb). Also included is the REE
pattern for modern seawater from 3000m (De Baar et al., 1985).
0.1 -- :

00 : : : : d- :


S ,- ,
0 .0 1 ,, ,, ,




0.001 --------------------
La Ce Pr Nd Sm Eu Gd Tb Ho Yb Lu
Figure 8-12 REE patterns from 8 sequential extractions. (A) Sites 608 and 647, (B) 689,
(C) 690, and (D) 982 for 3 different sediment fractions; the residue (res), the
Fe-Mn oxide coating (ox) and the carbonate (carb). Also included is the REE
pattern for modern seawater from 3000m (De Baar et al., 1985).