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Natural Gamma Activities in Glacimarine Sediments: Correlations with Terrestrial Source Data

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1 NATURAL GAMMA ACTIVITIES IN GLACIMARINE SEDIMENTS: CORRELATIONS WITH TERRESTRIAL SOURCE DATA By ALICE HILDICK 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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2 Copyright 2006 by Alice Hildick

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3 To those who endured it with me

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4 ACKNOWLEDGMENTS First, I would like to thank Dr. John Jaeger for his patience and he lp throughout the entire project. I would also like to thank those on the R/V Alpha He lix science crew who did the sampling for this study, and to Gillian Rosen for her countless hours of cons ult. I would like to thank Dr. Mike Perfit and Warren Gr ice for their help with petrogr aphic analysis, and Dr. Guerry McClellan for help with XRD analysis. A sp ecial thank you goes to my family, friends, and those at Geohazards, Inc. for their support throughout this process. Lastly I want to give a sincere thank you to Scott Purcif ull and Nicole Yonke, without whom this project never would have been finished.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES................................................................................................................ .........8 ABSTRACT....................................................................................................................... ............11 CHAPTER 1 INTRODUCTION..................................................................................................................13 2 BACKGROUND....................................................................................................................24 Regional Geology............................................................................................................... ....24 Icy Bay........................................................................................................................ ............25 Resurrection Bay............................................................................................................... .....25 Regional Glaciation............................................................................................................ ....25 Sedimentation.................................................................................................................. .......26 Transport an d Deposition.......................................................................................................27 Yakataga Formation............................................................................................................. ...28 Valdez Group................................................................................................................... .......29 Mineralogy..................................................................................................................... .........29 Radioisotopes.................................................................................................................. ........30 3 METHODS........................................................................................................................ .....36 Sampling....................................................................................................................... ..........36 Radioisotope Evaluation........................................................................................................ .37 Grain Size Separation.......................................................................................................... ...39 Mineralogy..................................................................................................................... .........40 Microscopic Evaluation...................................................................................................40 X-Ray Diffraction............................................................................................................40 4 RESULTS........................................................................................................................ .......46 Radioisotopic Analysis......................................................................................................... ..46 Mineralogy and Physical Properties.......................................................................................47 Core 249PC.....................................................................................................................47 Core 223BC.....................................................................................................................47 Grain Size..................................................................................................................... ..........48

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6 5 DISCUSSION..................................................................................................................... ....65 Grain Size..................................................................................................................... ..........65 Composition.................................................................................................................... ........66 Elemental Concentrations.......................................................................................................67 238U.............................................................................................................................. ....68 232Th............................................................................................................................. ....68 40K.............................................................................................................................. ......69 Clay Mineralogy................................................................................................................ .....71 Th/K Ratios.................................................................................................................... .........72 Possible Alteration/Biasing of Signal.....................................................................................72 Correlation with Aeroradiometric Data..................................................................................74 Correlation with Geochemical Data.......................................................................................75 6 CONCLUSION..................................................................................................................... ..79 LIST OF REFERENCES............................................................................................................. ..82 BIOGRAPHICAL SKETCH.........................................................................................................90

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7 LIST OF TABLES Table page 2-1 Half lives and average abundan ces of relevant radioisotopes...........................................35 3-1 Precision data for associated each ra dionuclide measured. The largest mean deviation about the mean measured was chosen to obtain greatest accuracy....................41 3-2 Elemental concentration data normalized to clay percent. The measured (original) concentrations are also listed for comparison. Only bulk sample measurements are presented...................................................................................................................... ......44 4-1 Radionuclide concentration data and asso ciated error of each bulk sample within each interval.................................................................................................................. .....49 4-2 Specific concentrations of elements within each core.......................................................53 4-3 Percent of clay-, siltand sand-sized fract ions from the two cores. The averages for each core are included at the bottom..................................................................................64

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8 LIST OF FIGURES Figure page 1-1 Satellite image of Alaska coastal margin showing extent of glaciation and sample environments (modified from MODIS Rapi d Response Project at NASA/GSFC, Gulf of Alaska Science Plan 2004)............................................................................................17 1-2 Location and geological map of area su rrounding core 223BC. Sediments within core 223BC are sourced by the Guyot Gl acier (courtesy of John Jaeger).........................18 1-3 Location and geological map of area surr ounding core 249PC. The core contains sediment sourced from Bear Glacier (modified from Bradley and Donley 1995, USGS).......................................................................................................................... ......19 1-4 Published uranium geochemical data in southern Alaska fr om lake and river sediment samples (modified from Weaver 1983)..............................................................20 1-5 Published thorium geochemical data of southern Alaska rive r and lake sediment samples. (modified from Weaver 1983)............................................................................21 1-6 Published potassium geochemical data from southern Alaska lake and river sediment samples (modified from Weaver 1983).............................................................................22 1-7 Aeroradiometric data of study area Source area surrounding core 249PC shows elevated K and Th, while the environment near core 223BC shows elevated U and K. Drainage basins are outlined. (modified from Saltus et al. 1999).....................................23 2-1 Structural formations on the southern Al aska margin (modified from Plafker et al. 1994).......................................................................................................................... ........32 2-2 Generalized sketch of the cross section near core 223BC.................................................33 2-3 Generalized sketch of the cr oss section surrounding core 249PC.....................................33 2-4 Mean annual precipitation for the stat e of Alaska. Note th at the area surrounding Resurrection Bay (core 249PC) has a range of 1501-5000 mm/yr while the area surrounding Icy Bay (core 223BC) shows levels from 3001-13000 mm/yr. (reprinted with permission from Spacial Climate Anal ysis Service, Oregon State University 2000).......................................................................................................................... ........34 3-1 Decay series of the 238U radioisotope releva nt to this study..............................................42 3-2 Decay series for the 232Th isotope......................................................................................43 4-1 Concentration of uranium with depth in core 249PC........................................................50 4-2 Concentration of thorium with depth in core 249PC.........................................................50

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9 4-3 Radioisotopic concentration of pot assium with depth in core 249PC...............................51 4-4 Concentration of uranium with depth in core 223BC........................................................51 4-5 Concentration of thorium with depth in core 223BC.........................................................52 4-6 Concentration of potassium with depth in core 223BC.....................................................52 4-7 Concentration of uranium with respect to percent clay for all intervals. After ~60% clay-sized material, there is a general increase of uranium concentration with increasing clay-sized material............................................................................................54 4-8 Concentration of thorium with respect to percent clay for all intervals............................54 4-9 Concentration of potassium with respect to percent clay for all intervals.........................55 4-10 Mineralogy of sand fraction with in core 249PC interval 0 cm....................................55 4-11 Mineralogy of sand fraction with in core 249PC interval 11 cm..................................56 4-12 Mineralogy of sand fraction fo r core 249PC interval 21 cm.......................................56 4-13 Mineralogy of sand fraction fr om core 223BC interval 15 cm....................................57 4-14 Mineralogy of sand fraction fr om core 223BC interval 20 cm....................................57 4-15 Typical image of core 249PC interval 0 cm showi ng mostly rock fragments (designated RF) with associated quartz. Field of view approximately 0.8 mm.................58 4-16 Image of biogenic material (designate d BM) among rock fragments in core 249PC interval 11 cm. Field of view approximately 0.8 mm.................................................58 4-17 Oxidized coating on grain from core 249P C interval 11 cm. This interval was the only one exhibiting coated grains. Fi eld of view approximately 1.25 mm........................59 4-18 Images of biotite (designated B) and accessory minerals from core 249PC interval 21 cm. Field of view approximately 1.25 mm.............................................................59 4-19 Typical picture of core 249PC interval 21 cm showing large rock fragments and quartz (designated Q). Field of view approximately 1.25 mm.........................................60 4-20 Image from core 223BC interval 15 cm. Rock fragments domina te but there is an increase in quartz and accessory minerals. Sand particles in this core are also more angular in shape. Field of view approximately 1.5 mm....................................................60 4-21 Typical image from core 223BC interv al 15 showing elevated abundances of plagioclase and amphibole, as well as in creased quartz (relative to core 249PC) among the dominant rock fragments. Field of view approximately 1.0 mm....................61

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10 4-22 Image of core 223BC interval 15 cm s ilt fraction. Field of view approximately 1.5 mm......................................................................................................................... ......61 4-23 Image of biotite among rock fragments a nd quartz grains from core 223BC interval 20 cm. Field of view approximately 0.8 mm..............................................................62 4-24 Image of core 223BC interval 20 cm silt fr action. The silt fragments are larger in general size as compared to the 15 cm interval of this co re. Field of view approximately 1.5 mm.......................................................................................................62 4-25 XRD data for both cores with associated mineralogy. Core 249PC is offset (raised) to better illustrate variations between cores.......................................................................63 5-1 Th/K ratio from core 249PC..............................................................................................77 5-2 Th/K ratio for core 223BC.................................................................................................77 5-3 Overlay of Th/K ratio for both cores.................................................................................78 5-4 Th/K ratio with percent clay for co res 223BC and 249PC showing little variation between them................................................................................................................... ..78

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11 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 NATURAL GAMMA ACTIVITIES IN GLACIMARINE SEDIMENTS: CORRELATIONS WITH TERRESTRIAL SOURCE DATA By Alice Hildick December 2006 Chair: John M. Jaeger Major Department: Geology The provenance analysis of fine-grained sedime nts is particularly important in continental margin environments where fine particles dominat e the stratigraphic record. One area receiving voluminous quantities of fine-grained material is the tectonically active southern Alaska margin, where sediment derived by glacial erosion is accumulating at some of the highest rates globally. Although the magnitude and rate of sediment deli very is known, little work has been done to determine the terrestrial sources and surficial pro cesses responsible for spatial heterogeneities in accumulation patterns. Natural gamma activities (238U, 232Th, and 40K) and mineralogy of two cores were examined at differing locations within the Gulf of Alaska (GOA) in an attempt to distinguish them using only these techniques. Cores were ch osen based on their differing lithologies, one core being comprised of material derived entire ly from the Valdez Group of the Chugach terrane, the other being comprised entirely of material from the Yakataga Formation (a ~5km thick marine and glacimarine clastic deposit of unknow n origin). Natural gamma activities were measured on a Canberra UltraLow Background Pl anar-Style germanium detector, mineralogy was determined by both XRD and petrographic analys es. In addition to bulk sample analysis, samples were separated into sand-, siltand clay -sized fractions to examine the association of

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12 grain size and radioistopic activity. Elemental concentrations of 238U, 232Th and 40K were compared to published geochemical river and stream sediment data. Measurements in this study fall well within ranges of parent sour ce material, revealing their accuracy as a provenance tool. Radioi sotopic activity measurements from each size fraction reveal an association of 238U, 232Th, and 40K with the fine-sized fr action, particularly of 40K with clay-sized fraction. The similarity between both natural gamma activities and mineralogy between cores suggest that sediments of both cores have the same source material. The Valdez Group is a well-estab lished member of the Chugach terrane, implying that the glacially-derived sediments of the Yakataga Form ation are also derived for the Chugach terrane.

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13 CHAPTER 1 INTRODUCTION Sediment source (provenance) identification is important in geological and environmental management fields for basin analysis. It is an important tool in tectonic reconstructions and in understanding weathering and tran sport processes, which help shape the topography observed today. Sediment provenance is used to constrain the sedimentary processes from erosion to final deposition, with the goal being to reconstruct parent-rock asse mblages of sediments and the climatic and physiographic conditions under which these sediments formed (Augustsson, Fanning, Munker, Bahlburg, and Jacobsen 2003; Weltje and Eynatten 2004). The provenance analysis of fine-grained sediments is particular ly important in continental margin environments, where these fractions dominate the stratigr aphic record. One ar ea receiving voluminous quantities (~250 x 106 tons/y; Jaeger, Nittrouer, Scott, and Milliman 1998) of fine-grained material is the Gulf of Alaska (GOA) margin, where sediment derived by glacial erosion is rapidly accumulating (Figure 1-1). Although the ma gnitude and rate of sediment delivery is known, there has been little provenance work done to determine the terrestrial sources and surficial processes responsible for the spat ial heterogeneities in accumulation patterns. Geochemical characteristics of sedimentary rocks are known to provide important clues to their provenance and depositional environmen ts. During the last few decades, geochemical study of sedimentary rocks has grown, particular ly in the area of provenance and source composition investigations (McLennan, Taylor and Kroner 1983; Fedo, Eriksson, and Krogstad 1996; Kampunzu, Cailteux, Moine, and Loris 200 5). Many provenance studies focus on sand fractions or bulk sediment samples, with heavy mineral analysis and rare earth element (REE) patterns being the dominant fingerprinting te chniques applied (Basu 2002; Kampunza et al. 2005; Kairyte, Stevens, and Egidijus 2005; Ny akairu and Koeberl 2001). Single grain

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14 techniques are used, but are only effective if their results can be firmly connected to the bulk mass transfer (Andersen 2004; Kairyte et al. 2005). Other criteria employed to identify sources include detrital thermochronology (using zircons or apatite), bulk composition analysis, and analysis of magnetic properties (Boggs 2001; Hounslow and Morton 2004; Liu, Zhu, and Li 2003; Watkins and Maher 2003). Sediments from many depositional environments, however, do not contain enough sand to make statistically significant petrographic determinations. Geochemical approaches to sedimentary provenan ce analysis are therefore especially useful where coarse sediment is scarce (McDan iel, McLennan, and Hanson 1997; Andrews and Principato 2002; Kairyte et al. 2005). Whereas REE and other trace elemental anal yses are a preferred method of studying the provenance of fine-grained sediments (Basu 2002; Weltje and Eynatten 2004), they are timeconsuming and expensive, and thus are not ideal for higher spatial resoluti on studies of sediment cores. For decades, the oil industry has used se veral wire-line logging tools (e.g., spectral gamma ray, photoelectric index) to provide high-resolu tion, continuous proxies of elemental abundances and mineralogy (Doveton 1994). Recently, Carter and Gammon (2004) used continuous gammaray spectroscopy on cores from ODP site 1119 on the Canterbury Margin of New Zealand to show climatically contro lled variability in the delivery of fine-grained 40K-rich glacial rock flour from the Southern Alps. Geochemical provenance studies have been succe ssful in using isotopic data to determine provenance and paleoclimate (Lang Farmer, Ayuso, and Plafker 1993; Schnyder, Deconick, and Boudin 2005) and fine-g rained sediments have proved to record accurately global paleoclimate evolution (Fabres, Calafat, Canals, Barcena, and Flores 2000). Southern Alaska has been referred to as an in situ natural laboratory to study the interaction of glacial and oroge nic processes, tectonics, and c ontinental margin sedimentation

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15 (Jaeger et al. 2001). The focus of this research is to use geochemical data at two separate locations (Figs. 1-2 and 1-3) within the GOA region to determin e (1) if grain-size and/or mineralogy plays a role in c ontrolling naturally occurring radioisotopic activities (238U, 232Th, 40K), and (2) the ability of these data to differe ntiate between two unique terranes in order to establish provenance. Detailed fluvial sedime nt geochemical data from stream and river sediment samples is available for comparison (Weaver 1983). (Figs. 1-4 through 1-6) Also available is an aeroradiometric survey map (Sa ltus, Riggle, Clark, and Hill 1999). (Figure 1-7) The hypothesis is that 238U is associated with zircons a nd heavy minerals being carried predominantly in the coarse (>63m) fraction, and 232Th and 40K are concentrated in the finesized fraction due to the presence of clays (illite, chlorite) and mica. If this is true, then bulk rocks within the source area for core 249PC (w hich is composed of more fine-grained, metasedimentary, flysch material of the Valdez Group) should contain lower 238U values and higher 232Th and 40K. The data from core 223BC should contain more coarse material (from the Yakataga Formation) and, therefor e, contain higher le vels of uranium relative to potassium and thorium. Other factors such as clay mineralogy and diagenesis are expected to play a role in radioisotopic activity, but will be minimal relative to grain size. If grain size does in fact play a role in controlling radioisotopic activities, then it could be possible to determine provenance based on this technique. Core location is important due to possible influences from ot her sources, such as changes in clay mineralogy, which might change the geoche mical signature. The two cores selected are each sourced by only one drainage basin. Core 2 23BC was taken 4 km from the ice front in Icy Bay, and core 249PC was taken just outside the mouth of Resurrec tion Bay near the termination of Bear Glacier. Based on core locations and a ssociated drainage basins, material associated

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16 with a source other than the Yakataga Forma tion for core 223BC or the Valdez Group for core 249PC is minimal. (Figure. 1-7)

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17 Figure 1-1. Satellite image of Alaska coasta l margin showing extent of glaciation and sample environments (modified from MODIS Rapid Response Project at NASA/GSFC, Gulf of Alaska Science Plan 2004).

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18 Figure 1-2. Location and geologi cal map of area surrounding core 223BC. Sediments within core 223BC are sourced by the Guyot Gl acier (courtesy of John Jaeger).

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19 Figure 1-3. Location and geologi cal map of area surrounding core 249PC. The core contains sediment sourced from Bear Glacier (modified from Bradley and Donley 1995, USGS). A LASKA Stud y Area

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20 249PC 223BC Figure 1-4. Published uranium geochemical data in southern Alaska from lake and river sediment samples (modifi ed from Weaver 1983).

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21 249PC 223BC Figure 1-5. Published thorium geochemical data of southern Alaska ri ver and lake sediment samples. (modified from Weaver 1983).

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22 249PC 223BC Figure 1-6. Published potassium geochemical data from southern Alaska lake and river sediment samples (modified from Weaver 1983).

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23 Figure 1-7. Aeroradiometric data of study area. Source area surrounding core 249PC shows elevated K and Th, while the environment near core 223BC shows elevated U and K. Drainage basins are outlined. (modified from Saltus et al. 1999).

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24 CHAPTER 2 BACKGROUND Regional Geology Southern Alaska is a geologically complex area of accreted terranes representing relict Paleozoic, Mesozoic, and Cenozoic arc-trench sy stems, oceanic plateaus, and flysch basins (Figure 2-1). The landward side of the Paci fic Plate boundary transf orm is a continental assemblage of five fault-bounded terranes that were accreted to the North American plate in the Mesozoic and Cenozoic. Additiona lly, the Yakutat terrane lies to the west of the FairweatherQueen Charlotte fault and is currently being accreted to southern Al aska (Monger and Berg 1984; Dobson, OLeary, and Veart 1998). Underthr usting and accretion of the Yakutat oceanic crust is apparent in a series of northeastwardto northward-dippi ng thrust faults. These include the Chugach-St. Elias, Contact, and Border Ra nges fault systems (Plafker 1987; Mazzotti and Hyndman 2002). The accretion of southern Alaska is summar ized in steps by Hillhouse and Coe (1994). The core of Alaska was produced by the collision of th e Wrangellia and Peninsular terranes with the Nixon Fork and Yukon-Tanana terranes during th e interval 100 to 55 million years ago (Ma). This produced the crust of south-central Alas ka, the ensuing Kula plate motion then likely provided the means to close the latitude ga p between Wrangellia and the mainland. The counterclockwise rotation of s outhwestern Alaska most likely occurred 68 to 44 Ma as the latitude gap was closing. Volcanic complexes in the southern margin of the Chugach and Prince William terranes were added to Alaska after 55 Ma, carried by the Kula, then Pacific plates, respectively. Lastly, the ongoi ng accretion of the Yakutat mi croplate beginning around 30 Ma, has led to the uplift of the Chugach-St. Elias ranges bordering the GOA. It is currently amongst the most seismically and tectonically active regi ons in the world (Jaeger et al. 2001; Plafker,

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25 Nockelberg, and Lull 1989). Interactions betw een the Pacific plate and overlying Yakutat microplate with the North American plate near th e coastal margin have produced regions of high elevations and steep topogra phy (Mazzotti and Hyndman 2002). Icy Bay Icy Bay has a complex geometry due to the r ecession of the Guyot Glacier, which occupied the bay until approximately 100 years ago. The Guyot, Yahtse, and Tyndall Glaciers have all been receding since 1904 (Jaeger and Nittrouer 1999). The recession has opened up four smaller fjords within the bay that had previously been fill ed with ice, and has left a moraine in the lower reaches of the bay. Sediment deposition within Icy Bay was studied extensively by Jaeger and Nittrouer (1999) who found that sediment from me ltwater streams of Malaspina Glacier draining directly into the lower half of the bay greatly influence sediment input there. The drainage basin sits almost entirely among sediments of the Ya kataga Formation (Figure 1-2). The Guyot Glacier is a tidewater glacier de positing directly into Icy Bay a nd sourcing the site for core 223BC. Resurrection Bay The Resurrection Bay area is characterized as a fjord coastline. Resu rrection Bay is a deep glacially eroded segment of the GOA coastline. Broad alluvial fans were built by several creeks and the Resurrection River. Within a few hundred feet of shore steep slopes plunge hundreds of feet to the ocean bottom. Sediments in this fj ord are derived from Bear Glacier, which overrides topography comprised almost entirely of rocks of the Valdez Group. The 249PC core site is located just outside the mouth of Resurrection Bay. (Figure 1-3) Regional Glaciation Glacial activity has been an in tricate part of forming the t opography throughout Alaska. It is described by Molnia and He in (1982) as the single most important process controlling

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26 sediment distribution in the GOA continental ma rgin environment. The GOA area is bordered by high coastal mountains, which trap abundant mo isture off the north Pacific. The abundance of glacial meltwater and rapid glacial motion lead to some of the highest erosion rates on the planet (105 tons km2 y-1, Hallet, Hunter, and Bogen 1996). Gl aciation in the ar ea is extensive and glaciers currently cover about 74,705 km2 (5%) of Alaska, half of wh ich occurs in the Kenai, Chugach, and St. Elias Mountains rimming the northern GOA (Cal kin, Wiles, and Barclay 2001; Sauber and Molnia 2003). Most glaciers in so uthern Alaska are characterized as surging glaciers. The glaciers are more temperate compared to the Pola r North Atlantic (Jaeger et al. 2001; Dobson et al. 1998). Sedimentation Sedimentary deposits are instrumental in record ing the geologic and climatic evolution of modern environments. The history of uplift and glaciation in southern Al aska is recorded in sedimentary deposits throughout the Gulf region (Pla fker 1987; Martin 1993). High basal debris loads (up to 1.5 m thick, Powell and Molnia 1989) and rapid glacial flow combine to produce large volumes of siliclastic glacimarine sedi ment. Sedimentation rates from the coastal mountains of southern Alaska have been estima ted as the highest globa lly (Hallet et al. 1996; Hunter, Powell, and Lawson 1996; Powell and Molnia 1989). This rapid sedimentation is due to vigorous tectonic uplift, weakened bedrock, and heavy precipitation (Powell 1984; Hallet et al. 1996). Sediment delivery to the Gulf in southern Alaska is dominated by meltwater plumes in fjords and rivers emptying onto the shelf (Curra n et al. 2003; Jaeger and Nittrouer, accepted; Sharma 1979). Many streams originate at the termini of active valley glaciers and carry sediment loads of up to >1g/l (Molnia and Hein 1982). Dominant controls on tidewater sedimentation (relevant to Icy Ba y) are driven by seasonal fluctu ations in meltwater discharge (Jaeger 2002).

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27 Transport and Deposition It is important to consider the history of the sediment to help constrain possible environmental effects. Generalized images of the two sites are presente d. (Figs. 2-2, 2-3) The transport history of the particles analyzed from these two sites are relatively similar, because both are from a temperate fjord environment in the GOA. Both contain sediments characterized as rock flour, which were likely carried in meltwat er from the glacier bed in a relatively dark, cold, vegetation-free environment (Anderson, Long acre, and Kraal 2003). Initial weathering of the source rock (Valdez Group for core 249PC, Yakataga Formation for core 223BC) preceded erosion. Heavy storms and high rates of precipita tion (in the form of rain and snow) increase physical weathering in the Gulf environment, fa cilitating rapid erosion and transport of the sediment. Much of the sediment was incorporat ed into the respective glaciers which continually ground and crushed material as it moved down slope Additional sediment was eroded from the valley walls and incorporated as the glacier move d. Sediment fluxes into temperate fjords such as this are generally controlled by meltwater discharge and calving (Jaeger and Nittrouer 1999). Glacial meltwater containing the rock flour was likely released as an englacial or subglacial jet and rose as a turbulent plume, which mixed with ambient water until it finally settled out (Powell and Molnia 1989; Syvitski 1988). In this environm ent, the coarsest material settles out quickly (often within 1 km of glacier terminus, Cowan, Powell, a nd Smith 1988) while the bulk of the fine sediment moves away from the fjords. Much of the fine-sized fraction is often carried in suspension onto the outer shelf (Sharma 1979). Mean annual precipitation for the area near core 223BC is 100 cm higher than that of the area sourcing core 249PC (Figure 2-4). Rainfall amounts may affect sedimentation and transport processes including residence time, and ha ve been shown to cause large variations in meltwater runoff from glaciers in southern Alas ka (Cowan et al. 1988; Gustavson and Boothroyd

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28 1982). The environment near Resurrection Bay likely has a slightly more complex depositional history relative to Icy Bay. Th e presence of a moraine and pr oglacial lake (Bear Lake) at Resurrection Bay between the Bear Glacier terminus and the Gulf may act as a trap for sediment. Seasonal precipitation and extremely high sedime nt discharge rates in the Gulf area make specific determination of residen ce times difficult, and beyond the scope of this project. The residence times within small drainage basins in the GOA environment are known to be short, as sediment is rapidly transported to the ocean (Jaeger et al. 1998). Once material is deposited into the ocean, reside nce times of particles in the water column for both core sites are also estimated to be shor t based on observations of floc settling rates in other Alaskan tidewater fjords (Jaeger and Ni ttrouer 1999; Hill, Syvitski, Cowan, and Powell 1998). Re-suspension of bottom sediment allowing for increased residence in the water column is negligible because cores are taken in 145 m and 161 m water depth, and the wave orbital velocities necessary to re-suspe nd silt-sized bottom sediment only applies to depths < 40 m throughout the year and < 60 m for most of th e year (Jaeger and N ittrouer, accepted). Yakataga Formation The Guyot Glacier is the source of the major ity of sediments at core 223BC in Icy Bay. (Figure 1-2) Sediment sampled within the norther n part of Icy Bay is derived principally from Upper Tertiary (Miocene to Plei stocene) rocks of the Yakataga Formation. The Yakataga Formation is located in the middle of an area of convergence and uplift on the GOA margin and is composed of interbedded terrestrial, marine, glacimarine, and glacioflu vial deposits that can locally exceed 5 km thickness (Bruns and Schw ab 1983; Hamilton 1994). It represents rapid deposition of sediments consisting predominantly of sandstones, mudstones, siltstones, shale and conglomerates (Mazzotti and Hyndman 2002; Saube r and Molnia 2003). Glaciation recorded by the Yakataga Formation is attributed to orogeni c uplift and increased prec ipitation resulting from

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29 the collision of the Yakutat terrane with the No rth American plate (Tur ner 1992). Clay mineral suites (illite, kaolinite, chlorite and smectite) wi thin it are relatively similar to those of the modern shelf (Molnia and Hein 1982). Accumu lation of recycled sedimentary material comprising the Yakataga Formation is estimated to have begun near mid-Miocene. Valdez Group The other study site is in the Resurrecti on Bay area of the GOA. (Figure 1-3) The sediments here are supplied from the Bear Glacier which sits entirely wi th rocks of the Valdez Group of the Chugach terrane. This group, a seri es of arc-derived slope and trench clastic deposits that comprise the vast majority of the ou ter Kenai Peninsula, is part of a flysch sequence which forms the southern part of the Chug ach terrane (Ward, Moslow, and Finkelstein1987; Nockleberg et al. 1994). The sedimentary rocks that compose it have been derived largely from a Phanerozoic continental margin arc complex ch aracterized by igneous rocks (Plafker, Moore, and Winkler 1994). Latest Cretaceous to early Pa leocene arc-continent collision resulted in offscraping and accretion to the contin ental margin of the flysch, mixe d flysch and basaltic tuff, and basalt which principally comprise the Valdez Group (Lang Farmer et al. 1993; Lull and Plafker 1989). Precambrian crustal material is present, possibly derived from late Proterozoic or older metasedimentary and metaigneous ro cks (Lang Farmer et al. 1993). Mineralogy Most major glacimarine depositional systems are siliclastic (Powe ll and Molnia 1989). The clay mineral content is cont rolled principally by 1) climate a nd relief, 2) type (mineralogy) of weathered source material, 3) chemical co mposition of weathering so lutions, and 4) later diagenesis within the deposit ional environment (Brownlow 1996; Schnyder et al. 2005). The most common clay minerals in soils, sediments, and sedimentary rocks are kaolinite, illite, smectite clays, and chlorite clays (Brownlow 1996). The average clay-sized (<2 m) sediment

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30 in southern Alaska (Molnia and Hein 1982) is predominantly kaolinite + chlorite (61 %), intermediate illite (37 %), and low smectite (2 %), representing an immature sediment characterized by rapid mechanical weathering and little chemical alteration. Analysis of the nonclay mineralogy of the clay-sized fraction by Moln ia and Hein (1982) identified the presence of accessory minerals which include but arent limite d to quartz, feldspar, amphibole, and calcite. Radioisotopes Gamma-ray measurements are non -destructive, efficient met hods of formation evaluation and can be a valuable tool in both the environm ental and engineering fi elds (Nir-El 1997, Ayres and Theilen 2001). A study by Schnyder et al. (2005) notes the use of radioisotopes in a variety of geological applications, incl uding sequence stratigraphy (van Wagoner et al. 1990), reservoir characterization, diagenesis and mineral ch aracterization (Hurst 1990), and source-rock evaluation. Gamma-ray measurements detect variations in natural radioactivity originating from changes in concentrations of the trace elements uranium (U) and thorium (Th), as well as the more common rock-forming element potassium (K). The abundance and halflives of U, Th, and K (Table 2-1) make these three elements the dom inant sources of gamma-rays detected, and thus the most important natural radionuclides for ma ny geological studies (Ruffell and Worden 1999; Ayres and Theilen 2001). Decay of the parent radioisotope 238U gives rise to one of the uranium decay series. The isotopic composition and concentrations of uranium, thorium (and their associated daughter products) and potassium ha ve previously been used as a dating and fingerprinting tool (Blum 1995; Harlavan and Erel 2002; Blum and Erel 1997). Particularly for the purposes of this thesis, it is important to not e that clay mineralogy is controlled primarily by weathered source rock, climate, transport, and deposition, whic h then influence the spectral gamma-ray (SGR) response of the sediments (Schnyder et al 2005).

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31 Uranium and thorium have many host minerals in sedimentary rocks including clays, feldspars, phosphates, and zircons (McLennan et al. 2003; Weltje and Eynatten 2004). Thorium, which is widely distributed in igneous rocks, is c onsidered at least partiall y insoluble and thus is often concentrated in sediments during weathe ring (Schnyder et al. 2005). Both uranium and thorium tend to be highly concentrated in tr ace accessory minerals such as zircon, monazite, apatite, and sphene (Blum a nd Erel 1997). Potassium is a bundant in sediments and is concentrated particularly in alkali feldspar a nd biotite, it is considered soluble in aqueous solutions (White et al. 1999; Ruffell and Worden 1999). The amount of 238U in natural uranium accounts for 99.27 % of total uranium, and 232Th accounts for almost all (assumed 100%) of total thorium. 40K compromises an average of 0.0118% of to tal potassium, which is actually very significant because potassium is one of the ten most surface-abundant elements on earth (Irwin, VanMouwerik, Stevens, Seese, and Bash am 1997; Hutchison and Hutchison 1997).

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32 Figure 2-1. Structural formations on the southern Alaska margin (modified from Plafker et al. 1994).

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33 Figure 2-2. Generalized sketch of the cross section near core 223BC. Figure 2-3. Generalized sk etch of the cross section surrounding core 249PC.

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34 Figure 2-4. Mean annual precipit ation for the state of Alaska. Note that the area surrounding Resurrection Bay (core 249PC) has a range of 1501-5000 mm/yr while the area surrounding Icy Bay (core 223BC) shows levels from 3001-13000 mm/yr. (reprinted with permission from Spacial Climate Anal ysis Service, Oregon State University 2000).

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35 Table 2-1. Half lives and average ab undances of relevant radioisotopes Radioisotope 40K 232Th 238U Half-life (billion years) 1.27714.054.468 Upper continental crust Elemental abundance (ppm) 2800010.72.8 Activity (Bq/kg) 8704335 Activity (nCi/kg) 231.20.9 Activity (kCi/km3 ) 663.32.6 Oceans Elemental concentration (mg/liter) 3991x10-70.0032 Activity (Bq/liter) 124x10-70.04 Activity (nCi/liter) 0.331x10-80.0011 Ocean sediments Elemental abundance (ppm) 1700051 Activity (Bq/kg) 5002012 Activity (nCi/kg) 140.50.3

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36 CHAPTER 3 METHODS Sampling Piston core 249PC and box core 223BC were c hosen for this study based on the differing lithologies of their sediment sources. Also considered was the similar proximity to glacial termini (~4 km), with similar wa ter depths (~150 m). Using glaci er-proximal core sites allows for the assumption that post-de positional physical and chemical alteration is minimal (e.g., slumping, turbidity flows, biol ogical activity). The proximal location of these cores also increases the likelihood that these sediments accu rately represent source material, relative to cores taken further out onto the shelf. Core samples used in this study were collected on the R/V Alpha Helix during June and July 1995. Core location is important because it is necessary to minimize influences from other sources. Core 223 was taken in 145 m depth water approximately 4 km from the ice front in Icy Bay, a fjord located on the eastern side of the southern Alaska GOA margin. Core 249PC was taken close to Resurrection Bay in 161 m water de pth approximately 4 km from the coast, near Bear Glacier. These locations allow for minimal in fluence of material associated with a source other than the Yakataga Formation for core 223 BC or the Valdez Group for core 249PC. (Figs 12, 1-3) Core 249PC was separated into 10 cm intervals (0 cm, 11 cm, and 21 cm) at the University of Florida. During sampling a box co re was subsampled with a 15 cm-diameter, 50 cm-long subcore, creating core 223BC. Core 223 BC had been previously segmented into 1 cm intervals and placed in whirlpak bags. Intervals 11 cm, 15 cm, 20cm, and 31 cm were chosen based on availability and similarity to depths of core 249PC. The core 223BC site experiences higher sedimentation rates (>100 cm y-1; Jaeger and Nittrouer 1999) than those at the

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37 site of core 249PC (~ 1 cm y-1; Jaeger et al. 1998). Sediment depos itional rates at the site of core 249PC in Resurrection Bay have not been as tight ly constrained as those in Icy Bay but can assumed based on observations from surrounding areas (Jaeger et al. 1998). The sediments within core 249PC near Resurrection Bay, ther efore, represent a longer time period than sediment retrieved in the Icy Bay core. Radioisotope Evaluation Radioactivity measurements of 232Th, 238U and 40K were performed on dried and powdered sediment. These samples were counted on a Canberra UltraLow Background Planar-Style germanium detector at the Univ ersity of Florida. The amoun t of sample used varied by availability, but averaged 15 g for core 249PC and 12 g for core 223BC. Count times ranged from 80,240 to 160,993 seconds but averaged 90,245 (about 25 hours), in order to accurately measure activity and minimize error. Raw gamma spectroscopy data was processed by analyzing photopeaks generated using Gamma Genie software. Background levels were determined by running an empty sample jar and subtracting the background value for each region of interest in the sample spectra. Efficiency was determined by counting a sample (NIST standard) with kno wn activity and comparing it with the amount detected on the instrument at the University of Florida. Self-absorption correction factor calculations were made for radioisotopes with gamma decay energies of less than 200 keV, which for this study affects only measurements of 234Th (related to 238U activity) at the 63 keV photopeak. This technique invol ves direct gamma transmission measurements on sample and efficiency calibration standards (see Cutshall, Larsen, and Olsen 1983 for further explanation). Radionuclide activity determinations were made by converting the raw data from counts per minute (cpm) to decays per minute (dpm), then dividing by sample weight. The standard form of conversion from activity (dpm/g) to co ncentration (ppm) is a process requiring the

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38 conversion of activity to atom quantity. Concentr ation determinations for these analyses were done using efficiencies previously established from the Buffalo River and an estuary (with known concentrations) for the radioisotope of inte rest. The cpm value is determined by dividing the net peak area by counting time. The 63 keV photopeak corresponding to 234Th activity was examined to determine 238U activity (Figures 3-1, 3-2). A si milar technique was used to obtain 232Th activity by measuring photopeaks associ ated with activity of the daughter 228Ac (half life = 6.13 d). Though no specific measurement was made, th e daughter is assumed to be in secular equilibrium with 232Th (half life = 1.4x1010 yr), since it has a signifi cantly shorter half life and we assume minimal loss of 228Ra. For a more accurate measurem ent, weighted averages of two peaks associated with 228Ac (a high energy gamma-ray at 911 keV as well as the 338 keV ray) were used. Multiple photopeaks are often averaged for more accurate 228Ac measurements (NirEl 1997). Secular equilibrium is the condition in which th e rate of decay of th e daughter is equal to that of the parent, and most commonly occurs wh en the daughter has a sign ificantly shorter half life than the parent. For 232Th and 238U, the half lives are significantly longer than those of their daughters (Table 2-1), satisfying necessary conditi ons to enable this type of analysis (Faure 1986). 40K was measured directly at the 1461 keV photopeak. Precision was determined by running two random samples on three separate occasions and determining the mean deviation from the mean. Du e to the small data set and associated scatter, it is more appropriate to use this deviation as opposed to a standa rd deviation in order to better represent error. This procedure esta blished errors for the radionuclides (238U 0.7 ppm, 232Th 0.4 ppm, and 40K 0.1 %). The largest deviation for each particular element was selected. (Table 3-1)

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39 Grain Size Separation Grain size separation in prepar ation for radioisotopic analysis was done at the University of Florida using sieve and Sedigr aph analyses (Lewis and McConc hie 1994; Syvitski 1991). Dry sediment samples weighing approximately 10 g (core 249PC) or 2.5 g (core 223BC) were homogenized then put into 120 milliliter (ml) glass jars and soaked in a 0.05 % sodium metaphosphate (Na(PO4)5) solution overnight in order to he lp disaggregate pa rticles. Those showing signs of flocculation were soaked an additional day in 1.0 % Na(PO4)5 solution. Samples were placed in an ultrasonic bath for a minimum of 10 minutes be fore being wet-sieved through a 63 m sieve in order to isolate the sand-sized frac tion which was then dried and weighed. The silt fraction was isolated by addi ng de-ionized water and diluting the clay/silt mixture to improve settling velocity. The mixt ure of approximately 500 ml was then agitated and allowed to settle in a water column based on the application of Stokes Law (in accordance with Lewis and McConchie 1994). After the de signated time, the remaining liquid was siphoned leaving only the silt fraction. The clay frac tion was separated by siphoning followed by either centrifugation or drying in a low-te mperature (< 60 F) oven. Ra ndom samples were selected to run on the Sedigraph as a check to determine if any remaining silt was left in suspension, and was found to be negligible (<1%). Radioisotopic activity is normalized to the ma ss of the counted sample (i.e., dpm/g). The sand-sized (>63 m) fraction was separated and we ighed, then divided by the original mass to get percent sand. The fine-sized fract ion was then mixed with 0.05 % Na(PO4)5 and run on a Sedigraph 5100 analyzer to determine percent si lt and percent clay (error was found to be less than 0.6 % in each interval). Additionally, a ll intervals were normalized according to mass percent clay to eliminate biases associated wi th increased mass due to increased sand content (Table 3-2).

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40 Mineralogy Microscopic Evaluation Mineralogy of the sand-sized fraction was determin ed in part by analysis of smear slides constructed using techniques of the I.O.D.P. and Flemings et al. (2006). Slides were created by sprinkling a small amount of homogenized se diment on a 2.5 cm x 7.5 cm glass slide and dispersing it over the slide with a drop of deionized water. The sample was then dried on a hot plate at a low temperature for approximately 5 mi nutes. A drop of Norland optical adhesive and a 2.5 cm x 2.5 cm cover glass were placed over the sample. The slide was then put under an ultraviolet light to dry and se t. Point count data was done on a Nikon petrographic microscope with an integrated auto matic point counter. Slides were anal yzed at 1000 counts per slide spaced at approximately 1 mm. X-Ray Diffraction Bulk mineral analysis of homogenized sedi ment was prepared for conventional powder mount x-ray diffraction (XRD) in accordance with Lewis and McConchie (1994) and done at the University of Florida. Approximately 2 g of sedi ment was taken from a central interval in each core (11 cm for core 249PC, 15 cm for core 223BC).

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41 Table 3-1. Precision data for associated each radionuclide measured. The largest mean deviation about the mean measured was chosen to obtain greatest accuracy. U (ppm) Th (ppm) K (%) run 1 3.5 5.91.5 run 2 2.8 5.41.6 run 3 2.1 6.61.5 Average 2.8 5.91.5 mean deviation 0.7 0.40.04 run 1 3.2 3.72.1 run 2 3.2 3.22.4 run 3 3.7 2.70.1 Average 3.4 3.22.2 mean deviation 0.2 0.30.1

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42 Figure 3-1. Decay series of the 238U radioisotope releva nt to this study. 234 Th 230 Th 238 U 234 U 234 Pa 218 Po 218 At 222 Rn 226 Ra 214 Bi 214 Po 218 Rn 214 Pb

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43 Figure 3-2. Decay series for the 232Th isotope. 228 Ra 224 Ra 232 Th 228 Th 228 Ac 212 Pb 212 Bi 216 Po 220 Rn 208 Ti 208 Pb 212 Po

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44 Table 3-2. Elemental concentration data normalized to clay percent. The measured (original) concentrations are also listed for comparison. Only bulk sample measurements are presented. Concentrations (normalized to clay) Original Concentrations DEPTH U (ppm)Th (ppm) K (%) U (ppm) Th (ppm) K (%) CORE 249PC 249 PCa 0 cm 6.44.73.54.53.1 2.5 249 PCb 0 cm 5.68.13.24.05.8 2.3 249 PCc 0 cm 6.07.03.44.25.0 2.4 249 PCa 110 cm 5.66.13.44.04.4 2.4 249 PCb 110 cm 6.15.93.34.34.3 2.4 249 PCc 110 cm 6.47.23.44.65.2 2.4 249 PCa 210 cm 7.29.23.94.15.3 2.2 249 PCb 210 cm 8.810.04.05.05.8 2.3 249 PCc 210 cm 7.211.44.04.16.6 2.3 CORE 223BC 223 BC 112 cm 1.63.72.43.74.1 2.0 223 BC 156 cm 4.85.02.63.23.4 1.8 223 BC 201 cm 4.10.80.42.40.6 0.3 223 BC 312 cm 2.73.21.41.72.1 0.9

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45

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46 CHAPTER 4 RESULTS Radioisotopic Analysis Core 249PC exhibited comparable concentra tions throughout the core for each element (Table 4-1, Figs. 4-1 through 4-6). The uranium concentration (ave raged from replicates of each interval) in core 249PC ranged from 4.2 ppm to 4.4 ppm, whereas in core 223BC it ranged from 1.7 ppm to 3.7 ppm. Thorium concentration in core 249PC ranged from 4.6 ppm to 5.9 ppm as opposed to the core 223BC range of 0.6 ppm to 4.1 pp m. The potassium percentage also showed more consistency in core 249PC, ranging from 2.3 % to 2.4 %, whereas core 223BC ranged from 0.3 % to 2.0 %. Although core 223BC did show increased variability in ranges of element concentrations, there remained a consistent ove rall decrease of activity with depth. Uranium showed a relatively linear trend of decreasing co ncentration with increa sed depth. The thorium concentration in core 223BC decreases in gene ral, the exception being interval 20 cm, which exhibited low thorium and potassium. This interval was different from all other intervals in that it exhibited a significantly hi gher uranium (2.4 ppm) concentration relative to extremely low thorium (0.6 ppm) and potassium (0.3 %). Detailed concentration data on separated size fractions is shown in Table 4-2. There is little evidence that elemental thorium concentrations are enhanced within a particular size fraction for either core, it is at times highest in each of the three size fractions. The concentration of uranium is not associated with the sand-sized fr action. It is always high est in either the clayor silt-sized fraction, bu t varies between the two. For potassium there is a distinct correlation of concentration and grain size thr oughout both cores. The clay (<2 m) fraction contains the highest concentration relative to si lt and sand at every interval. Th e potassium percentage is also lowest in the sand fraction at every interval. Each element is plotted against clay percent. (Figs.

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47 4-7 through 4-9) Concentration data once norma lized to clay, which assumes 100 percent claysized material, is shown compared to bulk concentration. (Table 3-2) Mineralogy and Physical Properties Core 249PC Mineralogic data for all thr ee intervals of core 249PC show ed a higher abundance of rock fragments (ranging from 78-86%) when compared to core 223BC (61-68%). (Figs. 4-10 through 4-14) There was also an appr eciable amount of quartz in co re 249PC (9-11%) at all three intervals. Biotite and amphibole were the next most common minerals. Accessory minerals compromising less than 1% of the sample incl ude, but are not limited to, pyroxene, garnet, biogenic material, opaque minerals (hematite, ilmenite), and glass (Figs. 4-15 through 4-24). Core 223BC Due to the limited amount of sand availabl e for core 223BC intervals 11 cm and 31 cm, no smear slides were made. Point count data for core 223BC on intervals 20 cm and 15 16 cm (the only two slides for core 223BC) s how an overall decrease in rock fragments and increase in quartz [relative to 249PC]. (Figs. 4-13, 4-14) Quartz abundances for core 223BC (22 % and 27 %) were at least twice that of those observed in core 249PC. The core 223BC interval containing fewer rock fragments (15 cm) had a corresponding increase in quartz fragments (27%). Biotite occurrence is at 4% for both intervals, while amphibole and accessory minerals show a slight (1% to 2%) in crease in the 15 cm segment. Relative to core 249PC, core 223BC contains mo re quartz and fewer rock fragments, with a more angular shape. Minera logy of the fine-sized fraction is very similar between cores (Figure 4-25). From XRD analysis, the most significan t peak corresponds to quartz at 26.67 (at 2 Cu), and is noted again at secondary peaks (e.g., 50.21). The peaks corresponding to illite, chlorite, and kaolinite are all elevated in core 24 9PC relative to core 223BC. This is expected

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48 due to the higher percentage of clay in core 249PC relative to 223BC. Core 223BC contains one additional mineral (likely a feldspar) wh ich is not present at core 249PC. Grain Size Grain size separation shows an average of ~ 66% clay, ~26% silt, and ~8% sand for core 249PC from 0-30 cm, with specific intervals rangi ng from 57 % to 71 % clay. (Table 4-3) There is an increase in silt with dept h (22% to 31%), and an overall incr ease in sand (8% to 12%). The core 249PC interval 21 cm shows a significant decrease in percent cl ay and increase in percent sand (57% clay, 12% sand). Grain size averages for core 223BC are 62% clay, 33% silt, and 3% sand, with clay ranging from 58 % to 67 %. There is an overall sli ght decrease in percent clay with depth (67% to 61%). Contrastingly, there is an overall sli ght increase of both percent silt (31% to 38%) and percent sand (2% to 6 %) with depth. The exceptions are interval 15 cm which exhibits a slight decrease in percent silt from the interval above it, and interval 312 cm which exhibits distinctly low sand content.

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49 Table 4-1. Radionuclide concentration data and asso ciated error of each bul k sample within each interval. 238U (ppm) error 232Th (ppm) Error 40K (%) error 249PC 0cm 4.2 .74.60.42.4 .1 111cm 4.3 .74.70.42.4 .1 210cm 4.4 .75.90.42.3 .1 223BC1 112cm 3.7 .74.10.42 .1 156cm 3.2 .73.40.41.8 .1 201cm 2.4 .70.60.40.3 .1 312cm 1.7 .72.10.40.9 .1 Note: For core 249PC, the three bulk samples were averaged

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50 Figure 4-1. Concentration of uran ium with depth in core 249PC. Figure 4-2. Concentration of thor ium with depth in core 249PC. 0 5 10 15 20 25 0.01.0 2.03.0 4.05.06.0 7.08.0U (ppm)Depth (cm) 0-10cm 11-20cm 21-30cm 0 5 10 15 20 25 0.01.0 2.03.0 4.05.06.0 7.08.0Th (ppm)Depth (cm) 0-10cm 11-20cm 21-30cm

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51 Figure 4-3. Radioisotopic concentration of potassium with dept h in core 249PC. Figure 4-4. Concentration of uran ium with depth in core 223BC. 0 5 10 15 20 25 0.00.51.01.52.0 2.5 3.0K (%)Depth (cm) 0-10cm 11-20cm 21-30cm 0 5 10 15 20 25 30 35 0.00.5 1.0 1.52.02.53.0 3.5 4.04.55.0U (ppm)Depth (cm) 11-12cm 15-16cm 20-21cm 31-32cm

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52 Figure 4-5. Concentration of thor ium with depth in core 223BC. Figure 4-6. Concentration of potassi um with depth in core 223BC. 0 5 10 15 20 25 30 35 0.00.5 1.0 1.5 2.0 2.53.03.54.04.55.0Th (ppm)Depth (cm) 11-12cm 15-16cm 20-21cm 31-32cm 0 5 10 15 20 25 30 35 0.00.5 1.0 1.52.02.5K (%)Depth (cm) 11-12cm 15-16cm 20-21cm 31-32cm

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53 Table 4-2. Specific concentrations of elements within each core DEPTH 238U (ppm) 232Th (ppm) 40K (%) CORE 249PC 249 PCa 0 cm 4.53.12.5 249 PCb 0 cm 4.05.82.3 249 PCc 0 cm 4.25.02.4 249 PCclay 0 cm 3.94.32.7 249 PCsilt 0 cm 4.46.01.7 249 PCsand 0 cm 3.13.61.8 249 PCa 100 cm 4.04.42.4 249 PCb 100 cm 4.34.32.4 249 PCc 100 cm 4.65.22.4 249 PCclay 100 cm 6.04.02.8 249 PCsilt 100 cm 4.24.32.2 249 PCsand 100 cm 3.55.91.5 249 PCa 200 cm 4.15.32.2 249 PCb 200 cm 5.05.82.3 249 PCc 200 cm 4.16.62.3 249 PCclay 200 cm 5.34.42.7 249 PCsilt 200 cm 3.84.21.4 249 PCsand 200 cm 3.94.01.6 CORE 223BC 223 BC 112 cm 3.74.12.0 223 BCclay 112 cm 0.14.21.2 223 BCsilt 112 cm 2.30.80.8 223 BCsand 112 cm N/AN/AN/A 223 BC 156 cm 3.23.41.8 223 BCclay 156 cm 2.02.61.7 223 BCsilt 156 cm 2.95.11.2 223 BCsand 156 cm 0.23.90.3 223 BC 201 cm 2.40.60.3 223 BCclay 201 cm 2.22.81.7 223 BCsilt 201 cm 3.94.01.2 223 BCsand 201 cm 3.24.90.8 223 BC 312 cm 1.72.10.9 223 BCclay 312 cm 3.23.72.1 223 BCsilt 312 cm 1.93.20.3 223 BCsand 312 cm 0.10.30.1

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54 Figure 4-7. Concentration of uran ium with respect to percent clay for all intervals. After ~60% clay-sized material, there is a general increase of uranium concentration with increasing clay-sized material. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 0%10%20%30%40%50%60%70%80%% clay-sized materialTh (ppm) 249PC 0-10 249PC 11-20 249PC 21-30 223BC 11-12 223BC 15-16 223BC 20-21 223BC 31-32 Figure 4-8. Concentration of thorium with re spect to percent clay for all intervals. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 0%10%20%30%40%50%60%70%80%% clay-sized materialU (ppm) 249PC 0-10 249PC 11-20 249PC 21-30 223BC 11-12 223BC 15-16 223BC 20-21 223BC 31-32

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55 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0%10%20%30%40%50%60%70%80%% clay-sized materialK (%) 249PC 0-10 249PC 11-20 249PC 21-30 223BC 11-12 223BC 15-16 223BC 20-21 223BC 31-32 Figure 4-9. Concentration of potassium with respect to percent clay for all intervals. Figure 4-10. Mineralogy of sand fracti on within core 249PC interval 0 cm. 86% 9% 2% 2% 1% rock frags quartz amphibole biotite accessory

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56 Figure 4-11. Mineralogy of sand fracti on within core 249PC interval 11 cm. Figure 4-12. Mineralogy of sand fr action for core 249PC interval 21 cm. 78% 11% 3% 3% 5% rock frags quartz amphibole biotite accessory 82% 10% 3% 3% 2% rock frags quartz amphibole biotite accessory

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57 Figure 4-13. Mineralogy of sand frac tion from core 223BC interval 15 cm. Figure 4-14. Mineralogy of sand frac tion from core 223BC interval 20 cm. 61% 27% 5% 4% 3% rock frags quartz amphibole biotite accessory 69% 22% 3% 4% 2% rock frags quartz amphibole biotite accessory

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58 Figure 4-15. Typical image of core 249PC interval 0 cm showing mostly rock fragments (designated RF) with associated quartz. Field of view approximately 0.8 mm. Figure 4-16. Image of biogenic material (des ignated BM) among rock fragments in core 249PC interval 11 cm. Field of view approximately 0.8 mm. RF BM RF

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59 Figure 4-17. Oxidized coating on grain from co re 249PC interval 11 cm. This interval was the only one exhibiting coated grains. Field of view approximately 1.25 mm. Figure 4-18. Images of biotite (designated B) and accessory minerals from core 249PC interval 21 cm. Field of view approximately 1.25 mm. B B BM

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60 Figure 4-19. Typical picture of core 249PC interval 21 cm show ing large rock fragments and quartz (designated Q). Field of view approximately 1.25 mm. Figure 4-20. Image from core 223BC interval 15 cm. Rock fragments dominate but there is an increase in quartz and accessory minerals. Sand particles in this core are also more angular in shape. Field of view approximately 1.5 mm. RF RF Q

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61 Figure 4-21. Typical image from core 223BC interval 15 showing elevated abundances of plagioclase and amphibole, as well as in creased quartz (relative to core 249PC) among the dominant rock fragments. Field of view approximately 1.0 mm. Figure 4-22. Image of core 223BC interval 156 cm silt fraction. Field of view approximately 1.5 mm. RF Q

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62 Figure 4-23. Image of biotite among rock fragme nts and quartz grains from core 223BC interval 20 cm. Field of view approximately 0.8 mm. Figure 4-24. Image of core 223BC interval 201 cm silt fraction. The silt fragments are larger in general size as compared to the 15 cm interval of this core. Field of view approximately 1.5 mm. B B B B B B

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63 Figure 4-25. XRD data for both cores with associ ated mineralogy. Core 249PC is offset (raised) to better illustrate variations between cores.

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64 Table 4-3. Percent of clay-, siltand sand-sized fractions from the two cores. The averages for each core are included at the bottom. Total % clay Total % Silt Total % Sand 249PC 0cm 70 228 110cm 71 254 210cm 57 3112 223BC 112cm 67 312 156cm 66 304 201cm 58 366 312cm 61 390.3 Averages Avg. clay % Avg. silt % Avg. sand % 249PC 66 268 223BC 63 343

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65 CHAPTER 5 DISCUSSION Grain Size Core 249PC has a similar percentage of fi ne-sized sediment in the 0 and 11 cm intervals, with a decrease in sa nd due to a slight (1% and 3%) in crease in clay and silt. The 21 30 cm interval exhibits a signifi cant drop in clay and increase in sand from the two intervals above it. This influx of sand can be attributed to the 1964 earthquake, which corresponds to that interval given the sediment accumulation rate (~1 cm y-1, Jaeger et al. 1998). The earthquake epicenter was located in nearby Prince William Sound and accounted for extensive redistribution of sediments by tsunamis (Jaeger et al. 1998). Sand percentage at core 223BC increases st eadily downcore (2%, 4%, and 6%) until the 31 cm interval where it drops to 0.3 %. Due to the extremely high sedimentation rate in the northern Icy Bay location (>0.3 cm d-1, Jaeger 2002) and lack of steady-state deposition, inconsistencies with accumulation and grain size at depth are exp ected. Decreased sand could be attributed to increased precipi tation, which may substantially in crease meltwater discharge and associated velocity, and allow for deposition of the sand-sized fraction further from the glacial termini. The two sites reveal variations in transpor t environments, which may affect grain size distribution. The presence of a moraine a nd Bear Lake between Bear Glacier and the Resurrection Bay core 249PC site may act as a tr ap for grains silt-sized and larger, whereas Guyot Glacier is a tidewater glac ier, which deposits sediment dire ctly into Icy Bay (Figs 2-1, 22). This may also explain the lower relative cl ay percentages in core 223BC compared to core 249PC. Guyot Glacier is connected to the water body and contributes sediment directly into Icy Bay, allowing for extended suspension a nd distribution of the finer particles.

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66 Composition Mineralogy of the two cores is surprisingly similar. Both cores are from a temperate glacial environment in the GOA, which produces predominantly glacimarine rock flour, therefore, a general similarity in particle size and common rock -forming mineralogy (relative to other parts of the world) is e xpected. The almost identical re sults from both petrographic and XRD analyses are not expected based on differi ng source lithology and geological environments (Figs. 1-2, 1-3). The XRD patterns, when view ed together, are distinguished only by more welldefined peaks from the Icy Bay sample, and one or two additional minerals (likely feldspars, McClellan, verbal communication) at the same site (Figure 4-25). Differences in peak intensities are partly due to variations in clay mineralogy as well as increase d overall clay percentage in the 249PC sample. Higher proportions of clay-sized particles produce a less intense, muted appearance in graphs (Moore and Reynolds 1997). The mineralogic analyses (4-10 through 414) show nearly identical sedime nt compositions, even with regard to accessory minerals. The variation is principally in re lative percentages, the exception being the increase in biogenic material under accessory minera ls in core 249PC interval 11 cm. These findings indicating that the source rocks presented in the two core s ites may not be as differe nt as initially thought. No source has currently been determined for the Yakataga Formation. It is possible that the Chugach terrane, which is the source material fo r core 249PC sediments, is also the source for the Yakataga Formation sediments of core 223BC. The point count data for core 249PC shows an overall decrease in rock fragments with depth, and a slight elevation in amphibole, biotite, and accessory minerals for intervals 11 cm and 21 cm. The coarse-size fraction of both co res contains predominantly rock fragments, with the next most common occurrence being quartz (though core 223BC consists of nearly twice the quartz of core 249PC) Both cores also contain bi otite, amphibole, and accessory

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67 minerals in amounts of less than 5 percent. The weathering of diffe ring source rock types surrounding each basin should hypothetically produ ce differing clay-mineral percentages (Hein et al. 2003). Though relative clay-min eral percentages vary between th e cores, it is only a slight variation which can be attributed to differences in sedimentation processes between core sites, or seasonal sediment discharge fluctuations. Elev ated illite content at the Resurrection Bay area relative to the Icy Bay area seen in the XRD analysis was also recorded by Molnia and Hein (1982). A single depositional or ap eriodic event might alter source of sediment, and is a possible reason for elevated illite (e.g., floodi ng at an illite-rich drainage basin or rapid draining of a lake). Elemental Concentrations Elemental concentrations are predominantly due to mineralogy, diagentic changes of clay mineralogy, and adsorption processes (Ayres and Th eilen 2001). Elevated clay mineral contents (illite, chlorite) and overall cl ay-sized material percentages in core 249PC (Figure 4-25, Table 43) correspond to higher isotopic c oncentrations. Radioactivity is often associated with clayor fine-sized particles (v an Wijngaarden et al 2002, Anderson 2004, Naidu, Han, Mowatt, and Wajda 1995). Relatively high concentrations of K have been recorded in marine sedimentary rocks of the Valdez Group near Bear Glacier (Goldfarb and Borden 1982). The Aialik pluton outcrops discontinuously around the mouth of Resurre ction Bay, it is locally biotite-rich and may contribute to increased potassium levels (K usky, Bradley, Donley, Rowley, Haeussler 2003). In an attempt to better repres ent elemental concentrations, samples from this study were normalized to percent clay. (Table 3-2) Due to th e high amount of clay in itially in most of the intervals, relative concentrations of normalized da ta are similar to initial bulk concentration data, with an increase in specific concentrations. Core 249PC interval 21 cm has a high elemental concentration (in each of the th ree elements) with respect to the relatively low sand percentage

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68 (Figs 4-7 through 4-9). This may be due to th e catastrophic nature of the 1964 earthquake event that deposited the sediment. Material of a wide range of sizes was moved at an extremely rapid rate, which would allow for minimal disaggregat ing of clay particles before deposition and burial. 238U Though the averaged concentratio ns for uranium in core 249PC show an increase in activity with depth, it is not defi nitive. (Figure 4-1, Table 4-2). Based on the concentration data and associated errors (Figure 4-1) it is impossible to conclude there exists an increased uranium concentration with depth. There is, however, a general consistency of uranium elemental concentration in all intervals from core 249PC, even at the 21 cm interval, which contains considerably less clay. By analyzing a homogeni zed 10 cm sample, as was done for core 249PC, fluctuations in sedimentati on could be minimized, producing more consistent results. The uranium concentrations in core 223BC decrease with depth in an almost linear manner. The decrease in concentration corresponds to a decrease in clay and, therefore, supports the correlation of activity of this element with grain-size. At the 20 cm interval uranium is elevated relative to thorium (Table s 4-1, 4-2). This interval is the most similar to the hypothesis put forth regarding an increase in uranium with associated decr ease in potassium and thorium, and is the only interval where th is behavior is seen. The hypothesi s stated this might be due to heavy minerals concentrated in the sand fracti on. Based on the mineralogy observed in this study that conclusion is unlikely. 232Th Core 249PC shows an increase in the average concentration of thorium with depth. When errors are taken into account (F igure 4-2) the increase becomes unc lear. This results in thorium exhibiting a general consistency in elemental concentration among all intervals, much like the

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69 uranium concentration in this core. There is an increase in silt content (Table 4-3) with depth that may support the association of thorium with the silt-sized fraction. Due to lack of consistency, it is more accurate to associate th orium with the more gene ral fine-sized fraction (<63 m) than to specify either the clayor silt-s ized fraction. Thorium elemental abundance in core 223BC shows the same general decrease with depth as seen with uranium, except at the 20 21 cm interval where concentration significantl y lower than the other intervals. Thorium abundance in both cores is higher than uraniu m abundance, and can be related to initial mineralogy, since thorium is more abundant in the earth (10ppm) than uranium (2ppm) (Ruffell and Worden 1999). This interval exhibits the highest amount of sand (6 %) within the core, supporting the association of the fine-sized fract ion with thorium elemental concentration. The elevated thorium concentration relative to ur anium at both the Resurre ction Bay and Icy Bay core sites is also seen in published geoc hemical data. (Figs. 1-4 through 1-6) 40K The percentage of potassium in core 249PC fl uctuates very little (<1 %) and, therefore, does not specifically show a decrease with dept h. Potassium concentra tion only varies by 0.1% in each of the three intervals in the 249PC core. The concentration is highest in the clay fraction and lowest in the sand fraction at every interval. The consistenc y seen in potassium elemental abundance among samples for core 249PC is simila r to uranium and thorium. The sediment associated with core 249PC show s slightly elevated overall concentrations of all radioisotopes examined when compared to core 223BC, but is particularly noticeable with potassium. Core 223BC potassium concentrations range from 0.3 % (20 cm interval) to 2.0 % (11 12 cm interval). Core 223BC shows an overall d ecrease in potassium with depth, similar to the uranium and thorium concentration with depth seen in this core. The exception is a very low

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70 concentration at the 20 cm interval which co rresponds to the lowest amount of clay (58 %) and highest amount of sand (6 %) in the core. There is an obvious association of potassium with the clay fraction for both cores. Glacial meltwater is known to be rela tively high in potassium (Anders on 2004). Sediment discharged into the GOA is predominantly clay-sized and th us is the principal potassium source, since potassium is locked in the clay mineral latti ce and relatively immobile. Physical grinding of biotite grains during abrasion in this type of glacial environmen t also exposes the inner layer (potassium) cations (Anderson 2004). The releas e of potassium relative to plagioclase is promoted in colder climates due to this type of biotite weathering (Wh ite et al. 1999; Blum and Erel 1997) and thus contributes to overall potassium. The pota ssium radioisotope is spread through many rock-forming minerals (e.g., feldsp ar) as well as heavy minerals (Asadov, Krofcheck, and Gregory 2001), so a uniform signal ev en after separation into size fractions is not uncommon. In general, core 249PC exhibits a different (elevated) elemental abundance from that of core 223BC, particularly when normalized to mass percent clay (Table 3-2). The distinction can be associated with an elevated percentage of cl ay-sized grains at core 249PC (Table 4-3), since there is an association of concentration with the fine-sized fraction. Note that the low sand content in the 11 cm interval does not result in a low uraniu m concentration or elevated thorium and potassium. A higher accessory mineral co ntent was recorded for this interval, but was largely due to increased diat om tests and biogenic material. The initial hypothesis suggested that 238U (uranium) in the cores was associated with zircons or other heavy minerals which are resistant to weathering and, ther efore, concentrated predomin antly in the coarse (>63 m) fraction, and that 232Th (thorium) and 40K (potassium) are associated w ith clays (illite, chlorite)

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71 and mica. Uranium abundances are similar to thorium and potassium abundances at almost every interval. The intensity of the glacial abrasion can promote the release of dissolved uranium from rocks into the waters where it would be incorporated into th e fine-sized fractions (Taboada, Cortizas, Garcia, and Garcia-Rodeja 2006; Hodson 2002). The decrease in percent clay at the core 223BC 20 cm interval is a likely explanation for lower 232Th and 40K activities. Gamma-ray activity s hould be a function of grain size (Asadov et al. 2001), and appears to be recorded he re. With regard to potassium in particular, there seems to be an association with the fine-si zed fraction, (the dominant sediment mode in the GOA), and the clay-sized fraction specifically. Changes in clay mineralogy (decrease in potassium-rich illite clay relativ e to smectite clays) are thus likely responsible for decreasing natural gamma activities not associated w ith decrease in clay-sized sediments. Clay Mineralogy Clay mineral assemblages play an intricat e role in controlling radioactivity and are particularly informative of source rock composition (Naidu et al. 1995). This is primarily due to the fine-sized fraction comprising the majority of sediment discharged in the GOA and the association of potassium with th is fraction (Jaeger et al. 1998; Molnia and Hein 1982; Anderson 2004). Clays in the GOA are characterized by high am ounts of illite and chlor ite with traces of expandable clay minerals and little to no kao linite (Naidu et al. 1995; Molnia and Hein 1982). Based on XRD in this study there is a presence of kaolinite that is considered to be high relative to previous studies. This is attributed to kaolin ite having a tendency to flocculate and concentrate in shallow marine successions close to shore (Ruffell and Worden 1999). Kaolinite and expandable clays such as montmorillanite co ntain significantly less potassium (and thorium) relative to illite clays (Ayers and Theilen 2001; Ruffell and Worden 1999). Thus, if a decrease in the relative abundance of an element (e.g., po tassium) does not coincide with a significant

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72 decrease in the fine-sized fraction, it may simply be related to the clay minerals present, as well as the mineralogy of non-clay mine rals in the clay -sized fraction. Th/K Ratios It is suggested that the mobility of potassium and uranium and the relative concentration of thorium during weathering should re sult in clays with elevated Th/K and Th/U ratios (Schnyder et al. 2005). The Th/K ratio is used to recognize clay mineral, feldspar, and mica associations (Ruffell and Worden 1999). Clay mineral analyses and Th/K ratios help to distinguish long-term transgressive events as well as short-term flooding (Ruffell and Worden 1999). When these ratios are plotted, core 249PC exhi bits a mix of chlorite and illite, with most points falling close to each other due to the very consistent potassi um concentration. (Figs 5-1 through 5-3) Core 223BC shows a very consistent ratio of 2:1 for thorium and potassium. Core 223BC interval 2021 cm records the lowest concentration of both t horium and potassium. When the Th/K ratio is plotted against percent clay, there is little distin ction between the two cores. (Figure 5-4) The similarity of clay mineral percentages, as we ll as depositional processes would produce similar Th/K ratios once normalized to clay. Possible Alteration/Biasing of Signal It is important for this study to understand th e potential extent of ch emical weathering in the glacial environment, particularly for this ty pe of study, which assumes initial source material is represented accurately in the sedimentary reco rd. The geochemistry of a sedimentary deposit is often influenced by many variables other th an parent rock composition (Fralick 2003). Weathering can be the dominant process affectin g the geochemistry of sedimentary rocks, and physical weathering is the dominant process in glaci al environments. Mobility of elements is particularly hard to constrain in these types of cold weather environments. Uplift and erosion are actively occurring in the GOA, and they are a driving function for geochemical cycling.

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73 Additionally, runoff and temperat ure are two of the most impo rtant parameters controlling chemical weathering rates (Dessert, Dupre, Ga illardet, Francois, and Claude 2003; Derry and France-Lanord 1996). The nature of the temperate glaciers within the stud y area makes chemical alteration a possibility relative to colder climates due to the presence of wa ter at the glacier base. This allows the glacier to erode its bed and t hus provides conditions necessary for accelerated weathering (Anderson, Drever, Fr ost, and Holden 1999). The potential of a difference in uranium con centration between parent-rock and sediment deposited is greater than that of thorium or potassium in this type of environment (Ruffell and Worden 1999). Conditions on the southern Alaska margin are considered oxidizing and there is very little organic matter present. Under suffi ciently oxidizing conditi ons uranium is commonly soluble in water (as U+6), while thorium has low solubility (Faure 1986). The mineralogy of the sand fraction did not reveal heavy minerals typically associated w ith uranium and therefore must be broken down prior to deposition and incor porated into all size fractions. This even distribution could occur by disso lved uranium in the water column being transported in proglacial rivers and streams. Thorium and potas sium are both considered to be locked in the mineral lattice, and relatively immobile. The exception is thorium, which may be somewhat mobile in the water column. The GOA is considered an oxidizing environm ent, it is likely that reducing conditions would exist only after deposition. Post-depositional alterations ar e very unlikely considering the rapid accumulation of sediment at each site, and relatively short time-period represented in each core. Previous studies show that glacial me ltwater is likely the dominant factor governing elemental fluxes (White and Blum 1995; Anders on 2004). There are englacial and supraglacial flow paths transmitting water quickly to outlet str eams, allowing little opportunity to interact

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74 with rocks and sediments (Anderson et al. 1999; Collins 1979). Mountain ranges in very close proximity to the sea such as in southern Alaska minimize terr estrial storage, and sediments within the Gulf have previ ously been characterized as having undergone mild chemical weathering (Jaeger et al. 2001; Anderson 2004). Alteration is possible, but considered unlikely and very mild given the extremely high discharge rates. Correlation with Aeroradiometric Data Aerial gamma-ray surveys measure the flux of gamma-rays emitted by the radioactive decay of the elements 40K (potassium), 238U (uranium), and 232Th (thorium). These elemental abundances can be used as proxies for studies because different rocks and soils generally contain different amounts of these elements. Th us the aeroradiometric measurements obtained can be useful for locating intrus ive rocks and mapping rock units w ith a distinctive radioelement signature (Duval, Cook, and Adams 1971). The National Uranium Resource Evaluation (NURE) program was conducted by the U.S. Government to assess radioelement data (Duval 2001). The program included airborne gamma-ray spectrome try and magnetic data collection along with extensive geochemical sample collection and pr ocessing. Aeroradiometric surveys of 98 1 by 3 quadrangles were flown in Alaska between 1975 and 1980. The data, collected in 15 surveys flown approximately 400 feet high and spaced appr oximately 6 miles apart, were done by Texas Instruments (T.I.), Lockwood, Kessler and Bart lett (LKB), and AeroServices (Aero) under contract with the U.S. Government. The surveys typically penetrate the u pper 2 feet (Duval et al. 1971). There is little correlation with aeroradiometric data in this study. (Figure 1-7) Elevated uranium measured in sediments at the Resurrection Bay site (relative to Ic y Bay) are not depicted on the aeroradiometric map. There is a small area on the survey map near Resurrection Bay which shows the presence of ur anium, though it would not seem to be enough to influence the

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75 elevated concentration recorded in the sediment here, particularly when compared with those of the Icy Bay core. The aeroradiometric survey ma p shows an absence of thorium in the Icy Bay environment with a highly elevated uranium con centration, also not recorded in the measured data. One possible explanation for the elevated uranium concentration near Icy Bay on the aeroradiometric map is the preferential sorting of heavy minerals by aeolian transport processes. Aeolian transport has been shown to be effectiv e at zircon enrichment and produce very high Zr and Hf contents in loess deposits when compared to continental crust (Taylor 1983; McLennan et al. 2003). These zircon enrichments on the surfa ce near the Icy Bay environment would cause elevated uranium unrelated to parent rock materi al or the coarse fraction. There might also be biases in the aeroradiometric map due to extr apolation of data. The 6-mile spacing between flight-lines would require assump tions to be made about the areas not directly measured. The analysis then is that there is no overall correla tion of aeroradiometric maps with measured concentrations, and they should not be used for comparison with core mate rial in the southern Alaska environment. Correlation with Geochemical Data Geochemical data from river and stream sa mples (Figs. 1-4 thr ough 1-6) reveal very similar elemental abundances to t hose determined at the core site s. The thorium data suggest a concentration at both core locati ons with a range from <3.7 to 8.7 ppm. (Table 4-1) Thorium concentrations were slightly lo wer at core 223BC relative to core 249PC, but still fall within published ranges. Potassium concentrations of bo th published data and th at of this study show elevated concentrations in the core 249PC e nvironment relative to those at core 223BC. Uranium is also slightly elevated in both this study and published data at the 249PC site. Core 223BC published data suggests a concentration ranging from approximately 1.4 to 3.8 ppm,

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76 which is very close to what this study obser ved. The environment near core 249PC shows a range of 1.9 to 7.3 ppm in published data, which is also almost identical to what was observed in this study. Though the ranges for core 223BC are la rge relative to 249PC ranges, they are well within the concentrations of published geochemical data.

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77 Figure 5-1. Th/K ratio from core 249PC. Figure 5-2. Th/K ratio for core 223BC. 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 0.00.51.0 1.52.02.53.0 3.5 4.04.55.0 K (%)Th (ppm) 249Pc 0-10cm 249Pc 11-20cm 249PC 21-30cm 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 0.00.51.0 1.52.02.53.0 3.5 4.04.55.0 K (%)Th (ppm) 223BC 11-12cm 223BC 15-16cm 223BC 20-21cm 223BC 31-32cm

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78 Figure 5-3. Overlay of Th/K ratio for both cores Figure 5-4. Th/K ratio with percent clay fo r cores 223BC and 249PC showing little variation between them. 0 0.5 1.01.5 2.02.53.0 3.5 4.04.5 5.0 0.0 4.0 8.0 12.0 20.0 16.0 Th (ppm) K ( % ) kaolinite smectite chlorite Mixed layer clays illite micas feldspars Increasing Th/K ratio 223BC 249PC 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 10 20 3040 5060 70 80 % clayTh/K ratio 249PC 0-10cm 249PC 11-20cm 249PC 21-30cm 223 BC 11-12cm 223BC 15-16cm 223BC 20-21cm 223BC 31-32cm

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79 CHAPTER 6 CONCLUSION The hypothesis stated previously was that 238U was associated with zircons or other heavy minerals carried predominantly in th e coarse (>63m) fraction, and that 232Th and 40K were associated with clays (illite, chlorite) and mica in the fine-sized fraction. This was expected to produce an elevated 238U concentration in core 223BC, and an elevated 232Th and 40K concentration at core 249PC, since 249PC contai ns more fine-grained material. Though 249PC did show elevated 232Th and 40K concentrations due to a hi gher clay percentage, the 238U was also increased. This is indicative of the 238U radioisotope also being ca rried predominantly in the fine-sized fraction. This study shows no correlation between concen tration and the sand-sized fraction. The sand fraction has been shown to display a wide ra nge of radioactivity an d often produces results similar to those in this study (Blum and Erel 199 7; Ayers and Theilen 2001). The variability of 238U and 232Th with each interval makes it difficult to discern precisely where it is being carried, though it is can be generally associ ated with the fine-sized fraction. There is particularly good association of the 40K radioisotope with the clay-sized fraction, it is highes t there for each interval of both cores. Natural gamma activity in this study is thus c ontrolled primarily by grain size and not mineralogy, though clay mineral assemb lages do play a role in determining relative amounts of potassium. Previous studies have dete rmined that the radioactivity from potassium often dominates the natural activity of the sediment and can be used as a provenance tool (Ayers and Theilen 2001). The second part of the hypothesis suggested that if grain size di d play a role in controlling radioisotopic activities, then it could be possible to determine provenance based on the radioisotope analysis of each core. Though gr ain size does show a stro ng correlation with

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80 potassium, the similar overall clay percentage an d mineralogy of the two cores make a distinct provenance determination difficult. Overall con centrations of core 249PC are higher than those of core 223BC are therefore distinguishable, but not convincingly. It is very possible that the Chugach terrane associated with the Chugach and St. Elias Mountai ns is influencing the source material at both locations, thus disrupting the unique geological terrane characteristics. This would imply that the Valdez group and the Yakataga formation are composed of material from the Chugach terrane. Specific determination s ource material for the Yakataga formation is beyond the scope of this thesis, however, the si milarity in XRD and petrographic analyses supports a more similar source material than or iginally estimated. The slightly elevated radioactivity at core 249PC is then attributed to a combination of elevated fine-sized sediment and slightly elevated initial potassium content of the rock assemblages near Bear Glacier and Resurrection Bay. A secondary goal of the study was to test the validity of aer oradiometric data from the southern Alaska region. The noticeably hi gh uranium in core 223BC relative to 249PC illustrated in Figure 1-7 was not seen. This is like ly due to the misrepresentation of parent rock material by aeroradiometric data. The high ur anium levels recorded are attributed to concentrated near-surface coarse material deposition both by recedi ng glacial activity and aeolian processes. This would concentrate heav y minerals that werent incorporated into the finer fraction (such as zircons and monazite) in the coarse fraction while the fine-sized fraction was transported to the Gulf. Ce rtain storm-induced flooding resul ting in high sediment discharge will still carry some heav y minerals to the Gulf (possibly recorded in core 223BC interval 20 cm), however would not be significant enough to prevent a bias in aeroradiometric measurements at certain deposit ional environments. Inferrin g sediment provenance from the

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81 final product is anything but stra ightforward since it evolves as it is transported from the source, this affects the near-surface sediments measured by the aeroradiometric surveys in particular (Weltje and Eynatten 2004). This study shows that, in genera l, there is a correlation of ra dioisotope activity with grain size. The inconsistencies observe d reveal there are other factors, such as mineralogy and surface adsorption (particularly for 232Th), contributing to overall activity. Activity of the 40K isotope is the least affected by factors other than grain si ze, and correlates well wi th the amount of claysized material. The similarity of source mineralogy makes distinc tion between locations difficult. Results do show a slight distinction th e two cores, and thus it may be possible to use this technique for provenance determination be tween two more unique environments. Th/K ratios are consistently near 2:1 at core 223BC, wh ereas the ratio at core 249PC is variable. Also, the minimum 40K values of core 249PC are higher than the maximum ones at 223BC. Natural gamma activity in this study is then primarily controlled by amount of clay minerals and the potassium content of the clay mineral assemblage s, which has been recorded in other studies (Ayres and Theilen 2001; Carter and Gammon 2004) Naturally it would be ideal to apply a suite of current techniques to obtain the highest accuracy and precision for provenance determination. These techniques can be very time consuming and expensive. Geochemical data from stream and river samples (Weaver 1983) for the GOA margin correlates well with radioisotopic concentrations measured in this study, proving that it is a non-destructive and efficient way of accurately determining radioi sotope concentration. Given two more unique environments, this technique could be a very valuable provenance tool.

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82 LIST OF REFERENCES Andersen, T., 2004. Detrital zircons as tracers of sedimentary provenance: Limiting conditions from statistics and numerical simulation. Ch em. Geol. Science Direct online, Dec. 2004. Anderson, S.P., Drever, J.I., Frost, C.D., Hold en, P., 1999. Chemical weathering in the foreland of a retreating glacier. Geochi m. Cosmocim. Acta 64, 1173-1189. Anderson, S.P., Longacre, S.A., Kraal, E.R., 2003. Pa tterns of water chemistry and discharge in the glacier-fed Kennicott River, Alaska: ev idence for subglacial water storage cycles. Chem. Geol. 202, 297-312. Anderson, S.P., 2004. Glaciers show direct linkage betw een erosion rate and chemical weathering fluxes. Geomorphology 67 (1-2): 147-157. Andrews, J.T., Principato, S.M., 2002. Grain-si ze characterization and provenance of iceproximal glacial marine sediments. Geologica l Society of America Special Publications 203, 305-324. Asadov, A., Krofcheck, D., Gregory, M., 2001. Applica tion of g-ray spectrometry to the study of grain size distribution of beach and river sands. Mar. Geol. 179, 203-211. Augustsson, C., Fanning, M., Munker, C., Bahl burg, H., Jacobsen, Y., 2003. Sediment sources for the Late-Paleozoic SW South American Gondwana margin: Insights from U-Pb ages and Hf isotope compositions of single detrital zircons. Geological Society of America. 35, 390pp. Ayres, A., Theilen, F., 2001. Natural gamma-ra y activity compared to geotechnical and environmental characteristics of near surf ace marine sediments. J. Appl. Geophys. 48, 110. Basu, A., 2002. A perspective on quantitative prov enance analysis; Memorie Descrittive della Carta. Geologica dItalia 61, 11-22. Blum, J.D., 1995. Isotope Decay Data. In: Ahrens, T. J. (Ed.), Global Earth Physics, A Handbook of Physical Constant. A.G.U, pp. 271-282. Blum, J.D., Erel, Y., 1997. Rb-Sr isotope systema tics of a granitic so il chronosequence; the importance of biotite weathering. Geochim.Cosmochim. Acta 61, 3193-3204. Boggs, S. Jr., 2001. Principles of Sedimentology and Stratigraphy, third ed. Prentice-Hall, New Jersey. Brownlow, A.H., 1996. Geochemistry, s econd ed. Prentice-Hall, New Jersey. Bruns, T.R., Schwab, W.C., 1983. Structure maps and seismic stratigraphy of Yakataga segment of the continental margin, north ern Gulf of Alaska. Miscella neous Field Studies Map U. S. Geological Survey. Report: MF-1424, 20.

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86 Kusky, T.M., Bradley, D.C., Donley, D.T., Ro wley, D., Haeussler, P., 2003. Controls on intrusion of near-trench magmas of the Sa nak-Baranof belt, Alaska, during Paleogene ridge subduction, and consequences for for earc evolution, In: Siss on, V.B., Roeske, S., Pavlis, T.L. (Eds.), Geology of a Transp ressional Orogen Developed During a RidgeTrench Interaction Along the North Pacific Margin. Geol. Soc. America Spec. Paper 371, pp. 269. Lang-Farmer, G., Ayuso, R., Plafker, G., 1993. A coast Mountains provenance for the Valdez and Orca groups, southern Alaska, based on Nd, Sr, and Pb isotopic evidence. Earth Planetary Sci. Letters. Lewis, D.W., McConchie, D., 1994. Analytical Sedimentology, Chapman and Hall, New York. Liu, H., Zhu, R.X., Li, G.X., 2003. Rock magnetic pr operties of the fine-gra ined sediment on the outer shelf of the East China Sea: imp lication for provenance. Mar. Geol. 193, 195-20. Lull, J.S., Plafker, G., 1989. Geochemistry and pa leotectonic implications of metabasaltic rocks in the Valdez Group, southern Alaska, In: Dove r, J.H., Galloway, J.P. (Eds.), Geologic studies in Alaska by the U.S. Geological Survey. U.S. Geol. Survey Bulletin 1946, pp. 2938. Martin, G.C., 1993. Lithostra tigraphy, In: Risely, D.E. et al. (E ds.), Geologic Report for the Gulf of Alaska planning area. Mineral Ma nagement Service Report 92-0065, pp. 63-98. Mazzotti, S., Hyndman, R.D., 2002. Yakutat collis ion and strain transfer along the northern Canadian Cordillera. Geology, Geologi cal Society of America 30, pp. 495-498. McDaniel, D.K ., McLennan, S.M ., Hanson, G.N 1997. Provenance of Amazon Fan muds; constraints from Nd and Pb isotopes In: Fox, G.L. (Ed.), Proceedings of the Ocean Drilling Program, Scientific Results 155, pp. 169-176. McLennan, S.M ., Taylor, S.R ., Kroner, A ., 1983. Geochemical evolution of Archean shales from South Africa; I, The Swaziland and Pongola supergroups Precambrian Res. 22, no. 1-2, 93-124. McLennan, S.M., Bock, B., Hemming, S.R., Huro witz, J.A., Lev, S.M., McDaniel, D.K., 2003. The roles of provenance and sedimentary pro cesses in the geochemistry of sedimentary rocks; In: Lentz, D.R. (Ed.), Geochemist ry of Sediments and Sedimentary Rocks: Evolutionary Considerations to Mineral Deposit-Forming Environments, Geol. Assoc. Canada, Geotext 4, pp. 7-38. Monger, J.W.H. Berg, H.C., 1984. Lithotect onic Terrane Map of Western Canada and Southeastern Alaska; U.S. Geological Su rvey. Open-file Report 84-523, Part B. Molnia, B.F., Hein, J.R., 1982. Clay mineralogy of a glacially dominated, subarctic continental shelf; northeastern Gulf of Alas ka. J. Sediment. Petrol. 52, 515-527.

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87 Moore, D.M., Reynolds, R.C., 1997. X-Ray Diffracti on and the Identification and Analysis of Clay Minerals, second ed. Oxford, New York. Naidu, A.N., Han, M.W., Mowatt, T.C., Wajda, W ., 1995. Clay minerals as indicators of sources of terrigenous sediments, their transpor tation and deposition: Bering Basin, Russia-Alaskan Arctic. Mar. Geol. 127, 87-104. Nir-El, Y., 1997. Traceability in the amount-of-substance analysis of natural potassium, thorium and uranium by the method of passive gamma-ray spectrometry. Accreditation and Quality Assurance 2, pp. 193-198. Nockleberg, W.J., Brew, D.A., Grybeck, D., Y eend, W., Bundtzen, T.K., Robinson, M.S., Smith, T.E., 1994. Metallogeny and major mineral deposits of Alaska, In: Plafker, G., Berg, H.C. (Eds.), The Geology of North America, v. G1, The Geology of Alaska Geological Society of America, Boulder, CO, pp. 855-903. Nyakairu, G.W.A., Koeberl, C., 2001. Mineralogi cal and chemical comp osition and distribution of rare earth elements in clay-rich sediment s from central Uganda. Geochem. J. 35, 13-28. Plafker, G., 1997. Geology and petroleum potential of the northern Gulf of Alaska continental margin, In: Scholl, D.W., Grantz, A., Vedder, J.G. (Eds.), Geology and Resource Potential of the Continental Margin of Western North America and Ad jacent Ocean Basins, Earth Science Services. Circum-Pacific Council fo r Energy and Mineral Resources 6, Houston, TX, p.229-268. Plafker, G., Nockelberg, W.J., Lull, J.S., 1989. Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach terranes along the Trans-Alaska Crustal Transect in the Chugach Mountains and southern Coppe r River Basin, Alaska. J.Geophys. Res. 94, 4255-4295. Plafker, G., Moore, J.C., Winkler, G.R., 1994. Geology of the southern Alaskan margin, In: Plafker, G., Berg, H.C., (Eds.), The Geol ogy of North America, v. G-1, The Geology of Alaska, Geological Society of Am erica, Boulder, CO, pp. 389-449. Powell, R.D., 1984. Glacimarine processes and i nductive lithofacies mode ling of ice shelf and tidewater glacier sediments based on qua ternary examples. Mar. Geol. 57, 1-52. Powell, R.D., Molnia, B.F., 1989. Glacimarine sedi mentary processes, facies and morphology of the South-Southeast Alaska shelf and fjords. Mar. Geol. 85 (2-4), 359-390. Ruffell, A., Worden, R., 1999. Palaeoclimate anal ysis using spectral gamma-ray data from the Aptian (cretaceous) of southern Engla nd and southern France. Palaeogeography, Palaeoclimatology, Palaeoecology 155, 265-283. Saltus, R.W., Riggle, F.E., Clark, B.T., Hill, P. I., 1999. Merged aeroradiometric data for Alaska: USGS Open File Report 99-0016.

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88 Sauber, J., Molnia, B., 2003. Glacier ice mass fluctu ations and fault instab ility in tectonically active southern Alaska. Globa l and Planetary Change, Topi cal Volume "Ice Sheets and Neotectonics" 42, pp. 279-293. Sharma, G.D., 1979. The Alaskan shelf: Hydrographic, sedimentary, and geochemical environment, Springer-Verlag, New York. Schnyder, J., Ruffell, A., Deconinck, J., Baudi n, F., 2005. Conjunctive use of spectral gamma ray logs and clay mineralogy in defining late Jurassic-early Cretaceous paleoclimate change. Paleogeography, Paleocli matology, Paleoecology 229, 303-320. Stephansson, A., Gislason, S.R., Arnorsson, S., 2001. Dissolution of primar y minerals in natural waters II, Mineral saturati on state. Chem. Geol. 172, 251-276. Syvitski, J.P.M., 1988. On the deposition of se diment within glacie r-influenced fjords: Oceanographic controls. Mar. Geol. 85, 301-329. Syvitski, J.P.M., 1991. Principles, Methods and Applications of Par ticle Size Analysis, Cambridge University Press, Cambridge. Taboada, T ., Cortizas, A.M ., Garcia, C ., Garcia-Rodeja, E ., 2006. Particle-size fractionation of titanium and zirconium during weathering and pe dogenesis of granitic rocks in NW Spain, GEODERMA 131 (1-2), pp. 218-236. Taylor, S.R., McLennan, S.M., McCulloch, M.T. 1983. Geochemistry of Loess, Continental Crustal Composition and Crustal Model Ag es. Geochim. Cosmochim. Acta 47, 1897-1905. Turner, R.F. (Ed.), 1992. Geologic Report for the Gulf of Alaska Planning Area, OCS Report; MMS 92-0065. Van Wagoner, J.C., 1990. Sequence bounda ries in siliciclastic stra ta on the shelf; physical expression and recognition crit eria. AAPG Bulletin 74, pp. 1774-1775. Van Wijngaarden M., Venema, L.B., De Meijer, R.J., Zwolsman, J.J.G., Van Os, B., Gieske, J.M.J., 2002. Radiometric sand-mud characterisa tion in the Rhine-Meuse estuary Part A. Fingerprinting. Geomorphology 43, 87-101(15). Ward, L.G., Moslow, T.F., Finkelstein, K ., 1987. Geomorphology of a Tectonically Active, Glaciated Coast, South-Central Alaska, In: Fi tzgerald, D. M., and Rosen, P. S. (Eds.), Glaciated Coasts, Academic Press Inc., California, pp. 1-31. Watkins, S.J., Maher, B.M., 2003. Magnetic charact erisation of present-day deep-sea sediments and sources in the North Atlantic. Earth Pl anetary Sci. Letters 214 (3-4), pp. 379-394. Weaver, T.A., (project manager) (1983). The Ge ochemical Atlas of Alaska; Geochemistry Group, earth and space sciences division; Lo s Alamos National Laboratory, Los Alamos, NM, (GJBX-32; LA-9897-MS UC-51).

PAGE 89

89 Weltje, G.J., Eynatten, H., 2004. Quantitative provenance analysis of sediments: review and outlook. Sediment. Geol. 171, 1-11. White, A.F., Blum, A.E., 1995. Effects of clim ate on chemical weathering in watersheds. Geochim. Cosmochim. Acta 59, 1729. White, A.F., Blum, A.E., Bullen, T.D., Vivit, D. V., Schultz, M., Fitzpatrick, J., 1999. The effect of temperature on experimental and natural ch emical weathering rates of granitoid rocks. Geochim. Cosmochim. Acta 63, 3277-3291.

PAGE 90

90 BIOGRAPHICAL SKETCH Alice Hildick was born in Vermont on Februa ry 16, 1979. She grew up in Florida, where she graduated from Clearwater Central Catholic High School. She got her bachelors degree in geology from the University of Florida in 2001, wo rked for Geohazards, Inc., then returned to the University of Florida to get her Master of Science degree. She spent time working at GeoSierra, LLC in Atlanta for a brief period during her Masters research. Alices favorite things include traveling, su rfing, and wine.


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Title: Natural Gamma Activities in Glacimarine Sediments: Correlations with Terrestrial Source Data
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NATURAL GAMMA ACTIVITIES INT GLACIMARINE SEDIMENTS: CORRELATIONS
WITH TERRESTRIAL SOURCE DATA




















By

ALICE HILDICK


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

Alice Hildick































To those who endured it with me









ACKNOWLEDGMENTS

First, I would like to thank Dr. John Jaeger for his patience and help throughout the entire

proj ect. I would also like to thank those on the R/V Alpha Helix science crew who did the

sampling for this study, and to Gillian Rosen for her countless hours of consult. I would like to

thank Dr. Mike Perfit and Warren Grice for their help with petrographic analysis, and Dr. Guerry

McClellan for help with XRD analysis. A special thank you goes to my family, friends, and

those at Geohazards, Inc. for their support throughout this process. Lastly I want to give a

sincere thank you to Scott Purcifull and Nicole Yonke, without whom this proj ect never would

have been finished.












TABLE OF CONTENTS


page


ACKNOWLEDGMENTS .............. ...............4.....


LIST OF TABLES ............. ....._.. ...............7....


LIST OF FIGURES .............. ...............8.....


AB S TRAC T ............._. .......... ..............._ 1 1..


CHAPTER


1 INTRODUCTION ................. ...............13.......... ......


2 BACKGROUND .............. ...............24....


Regional Geology .............. ...............24....
Icy B ay............... ...............25..
Resurrection Bay .............. ...............25....
Regional Glaciation .............. ...............25....
Sedimentation .............. ...............26....
Transport and Deposition .............. ...............27....
Yakataga Formation ................. ...............28................
Valdez Group ................. ...............29.................
Mineralogy ................. ...............29.................
Radioisotopes ................. ...............30.................


3 METHODS .............. ...............36....


Sampling ................. ........... ...............36.......
Radioisotope Evaluation............... ...............3
Grain Size Separation .............. ...............39....
Mineral ogy ............... .........__ ...............40....
Microscopic Evaluation............... ...............4

X-Ray Diffraction............... ..............4

4 RE SULT S .............. ...............46....


Radioisotopic Analysis .........____............. ...............46.....
Mineralogy and Physical Properties ................ ...............47......_.__....
Core 249PC .............. ...............47....
Core 223 BC .............. ...............47....
Grain Size .............. ...............48....













5 DI SCUS SSION ............. ...... .__ ...............65..


G rain Size .............. ...............65....

Com position............... ..............6
Elemental Concentrations ............. ...... .__ ...............67...
238U .............. ...............68~~~~
232Th ............. ...... ._ ...............68...
40K.......... ...............69~~~~~~~~

Clay M ineralogy .............. ...............71....
Th/K Ratios............... ... .. .. ...........7

Possible Alteration/Biasing of Signal ........._.. ....___........_. ...........7
Correlation with Aeroradiometric Data ................. ...............74................
Correlation with Geochemical Data .............. ...............75....


6 CONCLU SION................ ..............7


LIST OF REFERENCES ................. ...............82......_.._ ....


BIOGRAPHICAL SKETCH .............. ...............90....










LIST OF TABLES


Table page

2-1 Half lives and average abundances of relevant radioisotopes ................. ............... .....35

3-1 Precision data for associated each radionuclide measured. The largest mean
deviation about the mean measured was chosen to obtain greatest accuracy. ...................41

3-2 Elemental concentration data normalized to clay percent. The measured (original)
concentrations are also listed for comparison. Only bulk sample measurements are
presented. ............. ...............44.....

4-1 Radionuclide concentration data and associated error of each bulk sample within
each interval ............. ...............49.....

4-2 Specific concentrations of elements within each core .............. ...............53....

4-3 Percent of clay-, silt- and sand-sized fractions from the two cores. The averages for
each core are included at the bottom............... ...............64.










LIST OF FIGURES


Figure page

1-1 Satellite image of Alaska coastal margin showing extent of glaciation and sample
environments (modified from MODIS Rapid Response Proj ect at NASA/GSFC, Gulf
of Alaska Science Plan 2004) ................. ................ ......... ........ ......... 17

1-2 Location and geological map of area surrounding core 223BC. Sediments within
core 223BC are sourced by the Guyot Glacier (courtesy of John Jaeger). ................... .....18

1-3 Location and geological map of area surrounding core 249PC. The core contains
sediment sourced from Bear Glacier (modified from Bradley and Donley 1995,
U SG S). .............. ...............19....

1-4 Published uranium geochemical data in southern Alaska from lake and river
sediment samples (modified from Weaver 1983) ................. ..............................20

1-5 Published thorium geochemical data of southern Alaska river and lake sediment
samples. (modified from Weaver 1983). ............. ...............21.....

1-6 Published potassium geochemical data from southern Alaska lake and river sediment
samples (modified from Weaver 1983). ............. ...............22.....

1-7 Aeroradiometric data of study area. Source area surrounding core 249PC shows
elevated K and Th, while the environment near core 223BC shows elevated U and K.
Drainage basins are outlined. (modified from Saltus et al. 1999). ............. ...................23

2-1 Structural formations on the southern Alaska margin (modified from Plafker et al.
1994). ............. ...............3 2....

2-2 Generalized sketch of the cross section near core 223BC. ................ .......................33

2-3 Generalized sketch of the cross section surrounding core 249PC. ................ ................33

2-4 Mean annual precipitation for the state of Alaska. Note that the area surrounding
Resurrection Bay (core 249PC) has a range of 1501-5000 mm/yr while the area
surrounding Icy Bay (core 223BC) shows levels from 3001-13000 mm/yr. (reprinted
with permission from Spacial Climate Analysis Service, Oregon State University
2000). ............. ...............3 4....

3-1 Decay series of the 238U radioisotope relevant to this study. ................ ............. .......42

3-2 Decay series for the 232Th isotope. .............. ...............43....

4-1 Concentration of uranium with depth in core 249PC. ........._._......___ ........._.....50

4-2 Concentration of thorium with depth in core 249PC. ......___ ....... ...............50










4-3 Radioisotopic concentration of potassium with depth in core 249PC. ........._.._.. .............51

4-4 Concentration of uranium with depth in core 223BC. ......___ .......___ ........._.....5 1

4-5 Concentration of thorium with depth in core 223BC. ....._._._ .... ... .__ ........._......52

4-6 Concentration of potassium with depth in core 223BC. ....._._._ .......___ ........._....52

4-7 Concentration of uranium with respect to percent clay for all intervals. After ~60%
clay-sized material, there is a general increase of uranium concentration with
increasing clay-sized material ...........__......___ ...............54....

4-8 Concentration of thorium with respect to percent clay for all intervals. .........................54

4-9 Concentration of potassium with respect to percent clay for all intervals. ......................55

4-10 Mineralogy of sand fraction within core 249PC interval 0-10 cm............... ..................55

4-11 Mineralogy of sand fraction within core 249PC interval 11-20 cm............... .................56

4-12 Mineralogy of sand fraction for core 249PC interval 21-30 cm. ............. ....................56

4-13 Mineralogy of sand fraction from core 223BC interval 15-16 cm............... ..................57

4-14 Mineralogy of sand fraction from core 223BC interval 20-21 cm. ................. ..............57

4-15 Typical image of core 249PC interval 0-10 cm showing mostly rock fragments
(designated RF) with associated quartz. Field of view approximately 0.8 mm. ................58

4-16 Image of biogenic material (designated BM) among rock fragments in core 249PC
interval 1 1-20 cm. Field of view approximately 0.8 mm. ......____ ..... ...._ ...........58

4-17 Oxidized coating on grain from core 249PC interval 11-20 cm. This interval was the
only one exhibiting coated grains. Field of view approximately 1.25 mm. ................... ....59

4-18 Images of biotite (designated B) and accessory minerals from core 249PC interval
21-30 cm. Field of view approximately 1.25 mm. ............. ...............59.....

4-19 Typical picture of core 249PC interval 21-30 cm showing large rock fragments and
quartz (designated Q). Field of view approximately 1.25 mm. ............. ....................60

4-20 Image from core 223BC interval 15-16 cm. Rock fragments dominate but there is an
increase in quartz and accessory minerals. Sand particles in this core are also more
angular in shape. Field of view approximately 1.5 mm ................. ................ ....__60

4-21 Typical image from core 223BC interval 15-16 showing elevated abundances of
plagioclase and amphibole, as well as increased quartz (relative to core 249PC)
among the dominant rock fragments. Field of view approximately 1.0 mm. .................. .61











4-22 Image of core 223BC interval 15-16 cm silt fraction. Field of view approximately
1.5 m m ............. ...............61.....

4-23 Image of biotite among rock fragments and quartz grains from core 223BC interval
20-21 cm. Field of view approximately 0.8 mm. ............. ...............62.....

4-24 Image of core 223BC interval 20-21 cm silt fraction. The silt fragments are larger in
general size as compared to the 15-16 cm interval of this core. Field of view
approximately 1.5 mm. ............. ...............62.....

4-25 XRD data for both cores with associated mineralogy. Core 249PC is offset (raised)
to better illustrate variations between cores ................. ...............63...............

5-1 Th/K ratio from core 249PC. ............. ...............77.....

5-2 Th/K ratio for core 223BC. .............. ...............77....

5-3 Overlay of Th/K ratio for both cores .............. ...............78....

5-4 Th/K ratio with percent clay for cores 223BC and 249PC showing little variation
between them ............. ...............78.....









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

NATURAL GAMMA ACTIVITIES INT GLACIMARINE SEDIMENTS: CORRELATIONS
WITH TERRESTRIAL SOURCE DATA

By

Alice Hildick

December 2006

Chair: John M. Jaeger
Major Department: Geology

The provenance analysis of Eine-grained sediments is particularly important in continental

margin environments where Eine particles dominate the stratigraphic record. One area receiving

voluminous quantities of fine-grained material is the tectonically active southern Alaska margin,

where sediment derived by glacial erosion is accumulating at some of the highest rates globally.

Although the magnitude and rate of sediment delivery is known, little work has been done to

determine the terrestrial sources and surfieial processes responsible for spatial heterogeneities in

accumulation patterns.

Natural gamma activities (238U, 232Th, and 40K) and mineralogy of two cores were

examined at differing locations within the Gulf of Alaska (GOA) in an attempt to distinguish

them using only these techniques. Cores were chosen based on their differing lithologies, one

core being comprised of material derived entirely from the Valdez Group of the Chugach terrane,

the other being comprised entirely of material from the Yakataga Formation (a ~5km thick

marine and glacimarine plastic deposit of unknown origin). Natural gamma activities were

measured on a Canberra UltraLow Background Planar-Style germanium detector, mineralogy

was determined by both XRD and petrographic analyses. In addition to bulk sample analysis,

samples were separated into sand-, silt- and clay-sized fractions to examine the association of









grain size and radioistopic activity. Elemental concentrations of 238U, 232Th and 40K were

compared to published geochemical river and stream sediment data.

Measurements in this study fall well within ranges of parent source material, revealing

their accuracy as a provenance tool. Radioisotopic activity measurements from each size

fraction reveal an association of 238U, 232Th, and 40K with the fine-sized fraction, particularly of

40K with clay-sized fraction. The similarity between both natural gamma activities and

mineralogy between cores suggest that sediments of both cores have the same source material.

The Valdez Group is a well-established member of the Chugach terrane, implying that the

glacially-derived sediments of the Yakataga Formation are also derived for the Chugach terrane.









CHAPTER 1
INTTRODUCTION

Sediment source (provenance) identification is important in geological and environmental

management fields for basin analysis. It is an important tool in tectonic reconstructions and in

understanding weathering and transport processes, which help shape the topography observed

today. Sediment provenance is used to constrain the sedimentary processes from erosion to final

deposition, with the goal being to reconstruct parent-rock assemblages of sediments and the

climatic and physiographic conditions under which these sediments formed (Augustsson,

Fanning, Munker, Bahlburg, and Jacobsen 2003; Weltje and Eynatten 2004). The provenance

analysis of fine-grained sediments is particularly important in continental margin environments,

where these fractions dominate the stratigraphic record. One area receiving voluminous

quantities (~250 x 106 tons/y; Jaeger, Nittrouer, Scott, and Milliman 1998) of fine-grained

material is the Gulf of Alaska (GOA) margin, where sediment derived by glacial erosion is

rapidly accumulating (Figure 1-1). Although the magnitude and rate of sediment delivery is

known, there has been little provenance work done to determine the terrestrial sources and

surficial processes responsible for the spatial heterogeneities in accumulation patterns.

Geochemical characteristics of sedimentary rocks are known to provide important clues

to their provenance and depositional environments. During the last few decades, geochemical

study of sedimentary rocks has grown, particularly in the area of provenance and source

composition investigations (McLennan, Taylor, and Kroner 1983; Fedo, Eriksson, and Krogstad

1996; Kampunzu, Cailteux, Moine, and Loris 2005). Many provenance studies focus on sand

fractions or bulk sediment samples, with heavy mineral analysis and rare earth element (REE)

patterns being the dominant "fingerprinting" techniques applied (Basu 2002; Kampunza et al.

2005; Kairyte, Stevens, and Egidijus 2005; Nyakairu and Koeberl 2001). Single grain









techniques are used, but are only effective if their results can be firmly connected to the bulk

mass transfer (Andersen 2004; Kairyte et al. 2005). Other criteria employed to identify sources

include detrital thermochronology (using zircons or apatite), bulk composition analysis, and

analysis of magnetic properties (Boggs 2001; Hounslow and Morton 2004; Liu, Zhu, and Li

2003; Watkins and Maher 2003). Sediments from many depositional environments, however, do

not contain enough sand to make statistically significant petrographic determinations.

Geochemical approaches to sedimentary provenance analysis are therefore especially useful

where coarse sediment is scarce (McDaniel, McLennan, and Hanson 1997; Andrews and

Principato 2002; Kairyte et al. 2005).

Whereas REE and other trace elemental analyses are a preferred method of studying the

provenance of fine-grained sediments (Basu 2002; Weltj e and Eynatten 2004), they are time-

consuming and expensive, and thus are not ideal for higher spatial resolution studies of sediment

cores. For decades, the oil industry has used several wire-line logging tools (e.g., spectral gamma

ray, photoelectric index) to provide high-resolution, continuous proxies of elemental abundances

and mineralogy (Doveton 1994). Recently, Carter and Gammon (2004) used continuous gamma-

ray spectroscopy on cores from ODP site 1 119 on the Canterbury Margin of New Zealand to

show climatically controlled variability in the delivery of fine-grained 40K-rich glacial rock flour

from the Southern Alps. Geochemical provenance studies have been successful in using isotopic

data to determine provenance and paleoclimate (Lang Farmer, Ayuso, and Plafker 1993;

Schnyder, Deconick, and Boudin 2005) and fine-grained sediments have proved to record

accurately global paleoclimate evolution (Fabres, Calafat, Canals, Barcena, and Flores 2000).

Southern Alaska has been referred to as an in situ natural laboratory to study the

interaction of glacial and orogenic processes, tectonics, and continental margin sedimentation









(Jaeger et al. 2001). The focus of this research is to use geochemical data at two separate

locations (Figs. 1-2 and 1-3) within the GOA region to determine (1) if grain-size and/or

mineralogy plays a role in controlling naturally occurring radioisotopic activities (238U, 232Th,

40K), and (2) the ability of these data to differentiate between two unique terranes in order to

establish provenance. Detailed fluvial sediment geochemical data from stream and river

sediment samples is available for comparison (Weaver 1983). (Figs. 1-4 through 1-6) Also

available is an aeroradiometric survey map (Saltus, Riggle, Clark, and Hill 1999). (Figure 1-7)

The hypothesis is that 238U is associated with zircons and heavy minerals being carried

predominantly in the coarse (>63 Cm) fraction, and 232Th and 40K are concentrated in the fine-

sized fraction due to the presence of clays (illite, chlorite) and mica. If this is true, then bulk

rocks within the source area for core 249PC (which is composed of more fine-grained,

metasedimentary, flysch material of the Valdez Group) should contain lower 238U values and

higher 232Th and 40K. The data from core 223BC should contain more coarse material (from the

Yakataga Formation) and, therefore, contain higher levels of uranium relative to potassium and

thorium. Other factors such as clay mineralogy and diagenesis are expected to play a role in

radioisotopic activity, but will be minimal relative to grain size. If grain size does in fact play a

role in controlling radioisotopic activities, then it could be possible to determine provenance

based on this technique.

Core location is important due to possible influences from other sources, such as changes

in clay mineralogy, which might change the geochemical signature. The two cores selected are

each sourced by only one drainage basin. Core 223BC was taken 4 km from the ice front in Icy

Bay, and core 249PC was taken just outside the mouth of Resurrection Bay near the termination

of Bear Glacier. Based on core locations and associated drainage basins, material associated









with a source other than the Yakataga Formation for core 223BC or the Valdez Group for core

249PC is minimal. (Figure. 1-7)

















































Figure 1-1. Satellite image of Alaska coastal margin showing extent of glaciation and
sample environments (modified from MODIS Rapid Response Proj ect at
NASA/GSFC, Gulf of Alaska Science Plan 2004).

















ahts Legend
eah Elevation
rT Gaore 0-300 m
301-6000


Co Glac;E 1501180



223 15f27130


; 4801-5100
-UPN GULFOF al pna Rver5101-5400


/C Braided Streams
I Lakes
10 0 10 20 km :
GI I~e

(A)

r 110 I(RI tI( I. DEPOSITS Alluvial. glacial. lake~. estuarine-. swamlp. landslide. 11...iJ p aln. and lar~h
a dpouals.
U CPPER TERTIA\RY ROCK;S Sandstone, siltstone. shale. mudstone sand conglomerate of the \:la..uarga
0 Formation. M~iocene to PI~o..erie- in.u;.x
rmT.. XIDDLE TERTIARY' ROCK;S Silisiorne salnd-l.r, .In1J or ,ansUI shale of the Poul Cr~eek Formation.
e~ ~ ~ Oligacene to Mliocene in age.
(U ~ 1T ~LOW.ER TERTIARY. ROCKiS Intensely defrmend manri and contmentld clastic rock~s ofthe~
O F Kulthizth and Haydon Peak; Frm~ations, Paleocene to Eocene in age.
LOWER TERTIARY~ ALLFIC YOLCArNIC ROCKS Intensely deformed marine mudstones and

r, CRE'TACEO L S ROCKS Cou.~ lil. I :1 11! ch anld IInC ;iange mousel: unC isll Of the Yiakatart Giroup.

O ICRETACEOUIS AND L PPER JI'RASSIC AfETAMLORPHICS Connsist of unnamed phyllite slate,
Q,.. schist. gr~eeschist. amlphibolite. gaciss, and migmatite in St. ELias Mlountains.



Figure 1-2. Location and geological map of area surrounding core 223BC. Sediments within
core 223BC are sourced by the Guyot Glacier (courtesy of John Jaeger).





I Studv Area


GEOLOGIC MAP OF
KENAI FIORDS
NATIONAL PARK
AND VICINITY
rilionlal Park. lantal "
Surficial deposht(Vuuateary)
Grasilndiarit(etir)
Vldkr~roup(Cretaccous)
Meiugllool~uplcKll irciac lotec(;accous)
P'illow hasalt (Terdam? about 57 Ma)
B~asl shulemed dikes I lertionr.Lbout S7 Ma)
1 Glsabbr oler Ieingvko s7Ma) I a
IIMeamerphiiu maloks offa lhnd (Crelmnus?)~


rI IL I


- 2-19 PCI


il~l i .1r 1

60Y -


0 5 10 MILES iI
O 5 10 15 KIL.OMPTERS






.""


Glr!fr~' Ilu\Ae


Figure 1-3. Location and geological map of area surrounding core 249PC. The core contains
sediment sourced from Bear Glacier (modified from Bradley and Donley 1995,

USGS).




















Study area


Figure 1-4. Published uranium geochemical data in southern Alaska from lake and river
sediment samples (modified from Weaver 1983).





























3aQPr


33?Rr


Figure 1-5. Published thorium geochemical data of southern Alaska river and lake sediment
samples. (modified from Weaver 1983).
























249PC 223BC

































Figure 1-6. Published potassium geochemical data from southern Alaska lake and river sediment
samples (modified from Weaver 1983).

































Ir1Eomete s


Figure 1-7. Aeroradiometric data of study area. Source area surrounding core 249PC shows
elevated K and Th, while the environment near core 223BC shows elevated U and K.
Drainage basins are outlined. (modified from Saltus et al. 1999).


K1L









CHAPTER 2
BACKGROUND

Regional Geology

Southern Alaska is a geologically complex area of accreted terranes representing relict

Paleozoic, Mesozoic, and Cenozoic arc-trench systems, oceanic plateaus, and flysch basins

(Figure 2-1). The landward side of the Pacific Plate boundary transform is a continental

assemblage of five fault-bounded terranes that were accreted to the North American plate in the

Mesozoic and Cenozoic. Additionally, the Yakutat terrane lies to the west of the Fairweather-

Queen Charlotte fault and is currently being accreted to southern Alaska (Monger and Berg

1984; Dobson, O'Leary, and Veart 1998). Underthrusting and accretion of the Yakutat oceanic

crust is apparent in a series of northeastward- to northward-dipping thrust faults. These include

the Chugach-St. Elias, Contact, and Border Ranges fault systems (Plafker 1987; Mazzotti and

Hyndman 2002).

The accretion of southern Alaska is summarized in steps by Hillhouse and Coe (1994).

The core of Alaska was produced by the collision of the Wrangellia and Peninsular terranes with

the Nixon Fork and Yukon-Tanana terranes during the interval 100 to 55 million years ago (Ma).

This produced the crust of south-central Alaska, the ensuing Kula plate motion then likely

provided the means to close the latitude gap between Wrangellia and the mainland. The

counterclockwise rotation of southwestern Alaska most likely occurred 68 to 44 Ma as the

latitude gap was closing. Volcanic complexes in the southern margin of the Chugach and Prince

William terranes were added to Alaska after 55 Ma, carried by the Kula, then Pacific plates,

respectively. Lastly, the ongoing accretion of the Yakutat microplate beginning around 30 Ma,

has led to the uplift of the Chugach-St. Elias ranges bordering the GOA. It is currently amongst

the most seismically and tectonically active regions in the world (Jaeger et al. 2001; Plafker,









Nockelberg, and Lull 1989). Interactions between the Pacific plate and overlying Yakutat

microplate with the North American plate near the coastal margin have produced regions of high

elevations and steep topography (Mazzotti and Hyndman 2002).

Icy Bay

Icy Bay has a complex geometry due to the recession of the Guyot Glacier, which occupied

the bay until approximately 100 years ago. The Guyot, Yahtse, and Tyndall Glaciers have all

been receding since 1904 (Jaeger and Nittrouer 1999). The recession has opened up four smaller

fj ords within the bay that had previously been filled with ice, and has left a moraine in the lower

reaches of the bay. Sediment deposition within Icy Bay was studied extensively by Jaeger and

Nittrouer (1999) who found that sediment from meltwater streams of Malaspina Glacier draining

directly into the lower half of the bay greatly influence sediment input there. The drainage basin

sits almost entirely among sediments of the Yakataga Formation (Figure 1-2). The Guyot

Glacier is a tidewater glacier depositing directly into Icy Bay and sourcing the site for core

223BC.

Resurrection Bay

The Resurrection Bay area is characterized as a fjord coastline. Resurrection Bay is a deep

glacially eroded segment of the GOA coastline. Broad alluvial fans were built by several creeks

and the Resurrection River. Within a few hundred feet of shore steep slopes plunge hundreds of

feet to the ocean bottom. Sediments in this fj ord are derived from Bear Glacier, which overrides

topography comprised almost entirely of rocks of the Valdez Group. The 249PC core site is

located just outside the mouth of Resurrection Bay. (Figure 1-3)

Regional Glaciation

Glacial activity has been an intricate part of forming the topography throughout Alaska. It

is described by Molnia and Hein (1982) as the single most important process controlling









sediment distribution in the GOA continental margin environment. The GOA area is bordered

by high coastal mountains, which trap abundant moisture off the north Pacific. The abundance

of glacial meltwater and rapid glacial motion lead to some of the highest erosion rates on the

planet (10' tons km2 -1l, Hallet, Hunter, and Bogen 1996). Glaciation in the area is extensive

and glaciers currently cover about 74,705 km2 (5%) of Alaska, half of which occurs in the Kenai,

Chugach, and St. Elias Mountains rimming the northern GOA (Calkin, Wiles, and Barclay 2001;

Sauber and Molnia 2003). Most glaciers in southern Alaska are characterized as surging

glaciers. The glaciers are more temperate compared to the Polar North Atlantic (Jaeger et al.

2001; Dobson et al. 1998).

Sedimentation

Sedimentary deposits are instrumental in recording the geologic and climatic evolution of

modern environments. The history of uplift and glaciation in southern Alaska is recorded in

sedimentary deposits throughout the Gulf region (Plafker 1987; Martin 1993). High basal debris

loads (up to 1.5 m thick, Powell and Molnia 1989) and rapid glacial flow combine to produce

large volumes of siliclastic glacimarine sediment. Sedimentation rates from the coastal

mountains of southern Alaska have been estimated as the highest globally (Hallet et al. 1996;

Hunter, Powell, and Lawson 1996; Powell and Molnia 1989). This rapid sedimentation is due to

vigorous tectonic uplift, weakened bedrock, and heavy precipitation (Powell 1984; Hallet et al.

1996). Sediment delivery to the Gulf in southern Alaska is dominated by meltwater plumes in

fj ords and rivers emptying onto the shelf (Curran et al. 2003; Jaeger and Nittrouer, accepted;

Sharma 1979). Many streams originate at the termini of active valley glaciers and carry

sediment loads of up to >1g/1 (Molnia and Hein 1982). Dominant controls on tidewater

sedimentation (relevant to Icy Bay) are driven by seasonal fluctuations in meltwater discharge

(Jaeger 2002).









Transport and Deposition

It is important to consider the history of the sediment to help constrain possible

environmental effects. Generalized images of the two sites are presented. (Figs. 2-2, 2-3) The

transport history of the particles analyzed from these two sites are relatively similar, because

both are from a temperate fjord environment in the GOA. Both contain sediments characterized

as rock flour, which were likely carried in meltwater from the glacier bed in a relatively dark,

cold, vegetation-free environment (Anderson, Longacre, and Kraal 2003). Initial weathering of

the source rock (Valdez Group for core 249PC, Yakataga Formation for core 223BC) preceded

erosion. Heavy storms and high rates of precipitation (in the form of rain and snow) increase

physical weathering in the Gulf environment, facilitating rapid erosion and transport of the

sediment. Much of the sediment was incorporated into the respective glaciers which continually

ground and crushed material as it moved down slope. Additional sediment was eroded from the

valley walls and incorporated as the glacier moved. Sediment fluxes into temperate fjords such

as this are generally controlled by meltwater discharge and calving (Jaeger and Nittrouer 1999).

Glacial meltwater containing the rock flour was likely released as an englacial or subglacial jet

and rose as a turbulent plume, which mixed with ambient water until it finally settled out (Powell

and Molnia 1989; Syvitski 1988). In this environment, the coarsest material settles out quickly

(often within 1 km of glacier terminus, Cowan, Powell, and Smith 1988) while the bulk of the

fine sediment moves away from the fjords. Much of the fine-sized fraction is often carried in

suspension onto the outer shelf (Sharma 1979).

Mean annual precipitation for the area near core 223BC is 100-200 cm higher than that of

the area sourcing core 249PC (Figure 2-4). Rainfall amounts may affect sedimentation and

transport processes including residence time, and have been shown to cause large variations in

meltwater runoff from glaciers in southern Alaska (Cowan et al. 1988; Gustayson and Boothroyd









1982). The environment near Resurrection Bay likely has a slightly more complex depositional

history relative to Icy Bay. The presence of a moraine and proglacial lake (Bear Lake) at

Resurrection Bay between the Bear Glacier terminus and the Gulf may act as a trap for sediment.

Seasonal precipitation and extremely high sediment discharge rates in the Gulf area make

specific determination of residence times difficult, and beyond the scope of this proj ect. The

residence times within small drainage basins in the GOA environment are known to be short, as

sediment is rapidly transported to the ocean (Jaeger et al. 1998).

Once material is deposited into the ocean, residence times of particles in the water column

for both core sites are also estimated to be short based on observations of floc settling rates in

other Alaskan tidewater fj ords (Jaeger and Nittrouer 1999; Hill, Syvitski, Cowan, and Powell

1998). Re-suspension of bottom sediment allowing for increased residence in the water column

is negligible because cores are taken in 145 m and 161 m water depth, and the wave orbital

velocities necessary to re-suspend silt-sized bottom sediment only applies to depths < 40 m

throughout the year and < 60 m for most of the year (Jaeger and Nittrouer, accepted).

Yakataga Formation

The Guyot Glacier is the source of the maj ority of sediments at core 223BC in Icy Bay.

(Figure 1-2) Sediment sampled within the northern part of Icy Bay is derived principally from

Upper Tertiary (Miocene to Pleistocene) rocks of the Yakataga Formation. The Yakataga

Formation is located in the middle of an area of convergence and uplift on the GOA margin and

is composed of interbedded terrestrial, marine, glacimarine, and glaciofluvial deposits that can

locally exceed 5 km thickness (Bruns and Schwab 1983; Hamilton 1994). It represents rapid

deposition of sediments consisting predominantly of sandstones, mudstones, siltstones, shale and

conglomerates (Mazzotti and Hyndman 2002; Sauber and Molnia 2003). Glaciation recorded by

the Yakataga Formation is attributed to orogenic uplift and increased precipitation resulting from









the collision of the Yakutat terrane with the North American plate (Turner 1992). Clay mineral

suites (illite, kaolinite, chlorite and smeetite) within it are relatively similar to those of the

modern shelf (Molnia and Hein 1982). Accumulation of recycled sedimentary material

comprising the Yakataga Formation is estimated to have begun near mid-Miocene.

Valdez Group

The other study site is in the Resurrection Bay area of the GOA. (Figure 1-3) The

sediments here are supplied from the Bear Glacier, which sits entirely with rocks of the Valdez

Group of the Chugach terrane. This group, a series of arc-derived slope and trench plastic

deposits that comprise the vast maj ority of the outer Kenai Peninsula, is part of a flysch sequence

which forms the southern part of the Chugach terrane (Ward, Moslow, and Finkelsteinl 987;

Nockleberg et al. 1994). The sedimentary rocks that compose it have been derived largely from

a Phanerozoic continental margin arc complex characterized by igneous rocks (Plafker, Moore,

and Winkler 1994). Latest Cretaceous to early Paleocene arc-continent collision resulted in off-

scraping and accretion to the continental margin of the flysch, mixed flysch and basaltic tuff, and

basalt which principally comprise the Valdez Group (Lang Farmer et al. 1993; Lull and Plafker

1989). Precambrian crustal material is present, possibly derived from late Proterozoic or older

metasedimentary and metaigneous rocks (Lang Farmer et al. 1993).

Mineralogy

Most maj or glacimarine depositional systems are siliclastic (Powell and Molnia 1989).

The clay mineral content is controlled principally by 1) climate and relief, 2) type (mineralogy)

of weathered source material, 3) chemical composition of weathering solutions, and 4) later

diagenesis within the depositional environment (Brownlow 1996; Schnyder et al. 2005). The

most common clay minerals in soils, sediments, and sedimentary rocks are kaolinite, illite,

smeetite clays, and chlorite clays (Brownlow 1996). The average clay-sized (<2 Clm) sediment









in southern Alaska (Molnia and Hein 1982) is predominantly kaolinite + chlorite (61 %),

intermediate illite (37 %), and low smeetite (2 %), representing an immature sediment

characterized by rapid mechanical weathering and little chemical alteration. Analysis of the non-

clay mineralogy of the clay-sized fraction by Molnia and Hein (1982) identified the presence of

accessory minerals which include but aren't limited to quartz, feldspar, amphibole, and calcite.

Radioisotopes

Gamma-ray measurements are non-destructive, efficient methods of formation evaluation

and can be a valuable tool in both the environmental and engineering Hields (Nir-El 1997, Ayres

and Theilen 2001). A study by Schnyder et al. (2005) notes the use of radioisotopes in a variety

of geological applications, including sequence stratigraphy (van Wagoner et al. 1990), reservoir

characterization, diagenesis and mineral characterization (Hurst 1990), and source-rock

evaluation. Gamma-ray measurements detect variations in natural radioactivity originating from

changes in concentrations of the trace elements uranium (U) and thorium (Th), as well as the

more common rock-forming element potassium (K). The abundance and half-lives of U, Th, and

K (Table 2-1) make these three elements the dominant sources of gamma-rays detected, and thus

the most important natural radionuclides for many geological studies (Ruffell and Worden 1999;

Ayres and Theilen 2001). Decay of the parent radioisotope 238U gives rise to one of the uranium

decay series. The isotopic composition and concentrations of uranium, thorium (and their

associated daughter products) and potassium have previously been used as a dating and

Eingerprinting tool (Blum 1995; Harlavan and Erel 2002; Blum and Erel 1997). Particularly for

the purposes of this thesis, it is important to note that clay mineralogy is controlled primarily by

weathered source rock, climate, transport, and deposition, which then influence the spectral

gamma-ray (SGR) response of the sediments (Schnyder et al. 2005).









Uranium and thorium have many host minerals in sedimentary rocks including clays,

feldspars, phosphates, and zircons (McLennan et al. 2003; Weltje and Eynatten 2004). Thorium,

which is widely distributed in igneous rocks, is considered at least partially insoluble and thus is

often concentrated in sediments during weathering (Schnyder et al. 2005). Both uranium and

thorium tend to be highly concentrated in trace accessory minerals such as zircon, monazite,

apatite, and sphene (Blum and Erel 1997). Potassium is abundant in sediments and is

concentrated particularly in alkali feldspar and biotite, it is considered soluble in aqueous

solutions (White et al. 1999; Ruffell and Worden 1999). The amount of 238U in natural uranium

accounts for 99.27 % of total uranium, and 232Th accounts for almost all (assumed 100%) of total

thorium. 40K compromises an average of 0.01 18% of total potassium, which is actually very

significant because potassium is one of the ten most surface-abundant elements on earth (Irwin,

VanMouwerik, Stevens, Seese, and Basham 1997; Hutchison and Hutchison 1997).























G E
s
P ~I
c *I~~
.,' .r.
.''L' Y


AL$A CAAA


-.*D


'r'
c, 40
r
n


rv"

; '


L1
~G'..,
x.

-i /i
J-
3


s-


1:If


IW Io nO mann


135"
I ALsKA CANADA


OF .4LAS A 4


Figure 2-1. Structural formations on the southern Alaska margin (modified from Plafker et al.

1994).














G~uyot Gldr er


Figure 2-2. Generalized sketch of the cross section near core 223BC.









Bear~lacier


Figure 2-3. Generalized sketch of the cross section surrounding core 249PC.


leeberg
(Ice Rafted Debris)





































~ Precipitation (rnr) Bol -soo
0-200 801-1000
201-250 1001-1500
251-300 1501-2000
ra I 1301-350 2001-3000
J 351-400 3001-5000 .
l~p~q I 1401-450 5001- 7000
., ~ .Ta I 1 451-500 7001-13000

Service. Oregon State University
Feb. 200


Figure 2-4. Mean annual precipitation for the state of Alaska. Note that the area surrounding
Resurrection Bay (core 249PC) has a range of 1501-5000 mm/yr while the area
surrounding Icy Bay (core 223BC) shows levels from 3001-13000 mm/yr. (reprinted
with permission from Spacial Climate Analysis Service, Oregon State University
2000).










Table 2-1. Half lives and average abundances of relevant radioisotopes
Rad ioisotope 40K 232Th 238U
Half-life (billion years) 1.277 14.05 4.468

Upper continental crust
Elemental abundance (ppm) 28000 10.7 2.8
Activity (Bqlkg) 870 43 35
Activity (nCilkg) 23 1.2 0.9
Activity (kCilkm3) 66 3.3 2.6

Oceans
Elemental concentration
(mg/Iiter) 399 1 x1 0 0.0032
Activity (Bqlliter) 12 4x1 07 0.04
Activity (nCilliter) 0.33 1 x1 0 0.0011

Ocean sediments
Elemental abundance (ppm) 17000 5 1
Activity (Bqlkg) 500 20 12
Activity (nCilkg) 14 0.5 0.3









CHAPTER 3
IVETHOD S

Sampling

Piston core 249PC and box core 223BC were chosen for this study based on the differing

lithologies of their sediment sources. Also considered was the similar proximity to glacial

termini (~4 km), with similar water depths (~150 m). Using glacier-proximal core sites allows

for the assumption that post-depositional physical and chemical alteration is minimal (e.g.,

slumping, turbidity flows, biological activity). The proximal location of these cores also

increases the likelihood that these sediments accurately represent source material, relative to

cores taken further out onto the shelf. Core samples used in this study were collected on the RVY

Alpha Helix during June and July 1995.

Core location is important because it is necessary to minimize influences from other

sources. Core 223 was taken in 145 m depth water approximately 4 km from the ice front in Icy

Bay, a fj ord located on the eastern side of the southern Alaska GOA margin. Core 249PC was

taken close to Resurrection Bay in 161 m water depth approximately 4 km from the coast, near

Bear Glacier. These locations allow for minimal influence of material associated with a source

other than the Yakataga Formation for core 223BC or the Valdez Group for core 249PC. (Figs 1-

2, 1-3)

Core 249PC was separated into 10 cm intervals (0-10 cm, 11-20 cm, and 21-30 cm) at the

University of Florida. During sampling a box core was sub sampled with a 15 cm-diameter, 50

cm-long subcore, creating core 223BC. Core 223BC had been previously segmented into 1 cm

intervals and placed in whirlpak bags. Intervals 11-12 cm, 15-16 cm, 20-21cm, and 31-32 cm

were chosen based on availability and similarity to depths of core 249PC. The core 223BC site

experiences higher sedimentation rates (>100 cm y l; Jaeger and Nittrouer 1999) than those at the









site of core 249PC (~ 1 cm y l; Jaeger et al. 1998). Sediment depositional rates at the site of core

249PC in Resurrection Bay have not been as tightly constrained as those in Icy Bay but can

assumed based on observations from surrounding areas (Jaeger et al. 1998). The sediments

within core 249PC near Resurrection Bay, therefore, represent a longer time period than

sediment retrieved in the Icy Bay core.

Radioisotope Evaluation

Radioactivity measurements of 232Th, 238U and 40K were performed on dried and powdered

sediment. These samples were counted on a Canberra UltraLow Background Planar-Style

germanium detector at the University of Florida. The amount of sample used varied by

availability, but averaged 15 g for core 249PC and 12 g for core 223BC. Count times ranged

from 80,240 to 160,993 seconds but averaged 90,245 (about 25 hours), in order to accurately

measure activity and minimize error. Raw gamma spectroscopy data was processed by

analyzing photopeaks generated using Gamma Genie software.

Background levels were determined by running an empty sample jar and subtracting the

background value for each region of interest in the sample spectra. Efficiency was determined

by counting a sample (NIST standard) with known activity and comparing it with the amount

detected on the instrument at the University of Florida. Self-absorption correction factor

calculations were made for radioisotopes with gamma decay energies of less than 200 keV,

which for this study affects only measurements of 234Th (related to 238U activity) at the 63 keV

photopeak. This technique involves direct gamma transmission measurements on sample and

efficiency calibration standards (see Cutshall, Larsen, and Olsen 1983 for further explanation).

Radionuclide activity determinations were made by converting the raw data from counts

per minute (cpm) to decays per minute (dpm), then dividing by sample weight. The standard

form of conversion from activity (dpm/g) to concentration (ppm) is a process requiring the









conversion of activity to atom quantity. Concentration determinations for these analyses were

done using efficiencies previously established from the Buffalo River and an estuary (with

known concentrations) for the radioisotope of interest. The cpm value is determined by dividing

the net peak area by counting time. The 63 keV photopeak corresponding to 234Th activity was

examined to determine 238U activity (Figures 3-1, 3-2). A similar technique was used to obtain

232Th activity by measuring photopeaks associated with activity of the daughter 228Ac (half life =

6.13 d). Though no specific measurement was made, the daughter is assumed to be in secular

equilibrium with 232Th (half life = 1.4x1010 yr), since it has a significantly shorter half life and

we assume minimal loss of 228Ra. For a more accurate measurement, weighted averages of two

peaks associated with 228Ac (a high energy gamma-ray at 911 keV as well as the 338 keV ray)

were used. Multiple photopeaks are often averaged for more accurate 228Ac measurements (Nir-

El 1997).

Secular equilibrium is the condition in which the rate of decay of the daughter is equal to

that of the parent, and most commonly occurs when the daughter has a significantly shorter half

life than the parent. For 232Th and 238U, the half lives are significantly longer than those of their

daughters (Table 2-1), satisfying necessary conditions to enable this type of analysis (Faure

1986). 40K was measured directly at the 1461 keV photopeak.

Precision was determined by running two random samples on three separate occasions and

determining the mean deviation from the mean. Due to the small data set and associated scatter,

it is more appropriate to use this deviation as opposed to a standard deviation in order to better

represent error. This procedure established errors for the radionuclides (238U f0.7 ppm, 232Th

f0.4 ppm, and 40K f0.1 %). The largest deviation for each particular element was selected.

(Table 3-1)









Grain Size Separation

Grain size separation in preparation for radioisotopic analysis was done at the University

of Florida using sieve and Sedigraph analyses (Lewis and McConchie 1994; Syvitski 1991). Dry

sediment samples weighing approximately 10 g (core 249PC) or 2.5 g (core 223BC) were

homogenized then put into 120 milliliter (ml) glass jars and soaked in a 0.05 % sodium

metaphosphate (Na(PO4)5) Solution overnight in order to help disaggregate particles. Those

showing signs of flocculation were soaked an additional day in 1.0 % Na(PO4)5 Solution.

Samples were placed in an ultrasonic bath for a minimum of 10 minutes before being wet-sieved

through a 63 Clm sieve in order to isolate the sand-sized fraction which was then dried and

weighed. The silt fraction was isolated by adding de-ionized water and diluting the clay/silt

mixture to improve settling velocity. The mixture of approximately 500 ml was then agitated

and allowed to settle in a water column based on the application of Stoke's Law (in accordance

with Lewis and McConchie 1994). After the designated time, the remaining liquid was siphoned

leaving only the silt fraction. The clay fraction was separated by siphoning followed by either

centrifugation or drying in a low-temperature (< 600 F) oven. Random samples were selected to

run on the Sedigraph as a check to determine if any remaining silt was left in suspension, and

was found to be negligible (<1%).

Radioisotopic activity is normalized to the mass of the counted sample (i.e., dpm/g). The

sand-sized (>63 Clm) fraction was separated and weighed, then divided by the original mass to

get percent sand. The fine-sized fraction was then mixed with 0.05 % Na(PO4)5 and run on a

Sedigraph 5100 analyzer to determine percent silt and percent clay (error was found to be less

than 0.6 % in each interval). Additionally, all intervals were normalized according to mass

percent clay to eliminate biases associated with increased mass due to increased sand content

(Table 3-2).









Mineralogy


Microscopic Evaluation

Mineralogy of the sand-sized fraction was determined in part by analysis of smear slides

constructed using techniques of the I.O.D.P. and Flemings et al. (2006). Slides were created by

sprinkling a small amount of homogenized sediment on a 2.5 cm x 7.5 cm glass slide and

dispersing it over the slide with a drop of deionized water. The sample was then dried on a hot

plate at a low temperature for approximately 5 minutes. A drop of Norland optical adhesive and

a 2.5 cm x 2.5 cm cover glass were placed over the sample. The slide was then put under an

ultraviolet light to dry and set. Point count data was done on a Nikon petrographic microscope

with an integrated automatic point counter. Slides were analyzed at 1000 counts per slide spaced

at approximately 1 mm.

X-Ray Diffraction

Bulk mineral analysis of homogenized sediment was prepared for conventional powder

mount x-ray diffraction (XRD) in accordance with Lewis and McConchie (1994) and done at the

University of Florida. Approximately 2 g of sediment was taken from a central interval in each

core (11-20 cm for core 249PC, 15-16 cm for core 223BC).












Table 3-1. Precision data for associated each radionuclide measured. The largest mean
deviation about the mean measured was chosen to obtain greatest accuracy.
U (ppm) Th (ppm) K (%)
run 1 3.5 5.9 1.5
run 2 2.8 5.4 1.6
run 3 2.1 6.6 1.5

Average 2.8 5.9 1.5
mean deviation 0.7 0.4 0.04

run 1 3.2 3.7 2.1
run 2 3.2 3.2 2.4
run 3 3.7 2.7 0.1

Average 3.4 3.2 2.2
mean deviation 0.2 0.3 0.1




























Figure 3-1. Decay series of the 238U radioisotope relevant to this study.


238
B







































Figure 3-2. Decay series for the 232Th isotope.













Table 3-2. Elemental concentration data normalized to clay percent. The measured (original)
concentrations are also listed for comparison. Only bulk sample measurements are


presented.
Concentrations (normalized to clay)


Original Concentrations


DEPTH U (ppm) Th (ppm) K (%) U (ppm) Th (ppm) K (%)


CORE 249PC
249 PCa
249 PCb
249 PCc

249 PCa
249 PCb
249 PCc

249 PCa
249 PCb
249 PCc

CORE 223BC
223 BC

223 BC

223 BC

223 BC


0-10 cm
0-10 cm
0-10 cm

11-20 cm
11-20 cm
11-20 cm

21-30 cm
21-30 cm
21-30 cm



11-12 cm

15-16 cm

20-21 cm

31-32 cm


4.4 2.4
4.3 2.4
5.2 2.4


3.7 2.4

5.0 2.6

0.8 0.4

3.2 1.4


4.1 2.0

3.4 1.8

0.6 0.3

2.1 0.9
































































45









CHAPTER 4
RESULTS

Radioisotopic Analysis

Core 249PC exhibited comparable concentrations throughout the core for each element

(Table 4-1, Figs. 4-1 through 4-6). The uranium concentration (averaged from replicates of each

interval) in core 249PC ranged from 4.2 ppm to 4.4 ppm, whereas in core 223BC it ranged from

1.7 ppm to 3.7 ppm. Thorium concentration in core 249PC ranged from 4.6 ppm to 5.9 ppm as

opposed to the core 223BC range of 0.6 ppm to 4. 1 ppm. The potassium percentage also showed

more consistency in core 249PC, ranging from 2.3 % to 2.4 %, whereas core 223BC ranged from

0.3 % to 2.0 %. Although core 223BC did show increased variability in ranges of element

concentrations, there remained a consistent overall decrease of activity with depth. Uranium

showed a relatively linear trend of decreasing concentration with increased depth. The thorium

concentration in core 223BC decreases in general, the exception being interval 20-21 cm, which

exhibited low thorium and potassium. This interval was different from all other intervals in that

it exhibited a significantly higher uranium (2.4 ppm) concentration relative to extremely low

thorium (0.6 ppm) and potassium (0.3 %).

Detailed concentration data on separated size fractions is shown in Table 4-2. There is

little evidence that elemental thorium concentrations are enhanced within a particular size

fraction for either core, it is at times highest in each of the three size fractions. The concentration

of uranium is not associated with the sand-sized fraction. It is always highest in either the clay-

or silt-sized fraction, but varies between the two. For potassium there is a distinct correlation of

concentration and grain size throughout both cores. The clay (<2 Clm) fraction contains the

highest concentration relative to silt and sand at every interval. The potassium percentage is also

lowest in the sand fraction at every interval. Each element is plotted against clay percent. (Figs.









4-7 through 4-9) Concentration data once normalized to clay, which assumes 100 percent clay-

sized material, is shown compared to bulk concentration. (Table 3-2)

Mineralogy and Physical Properties

Core 249PC

Mineralogic data for all three intervals of core 249PC showed a higher abundance of rock

fragments (ranging from 78-86%) when compared to core 223BC (61-68%). (Figs. 4-10 through

4-14) There was also an appreciable amount of quartz in core 249PC (9-1 1%) at all three

intervals. Biotite and amphibole were the next most common minerals. Accessory minerals

compromising less than 1% of the sample include, but are not limited to, pyroxene, garnet,

biogenic material, opaque minerals (hematite, ilmenite), and glass (Figs. 4-15 through 4-24).

Core 223BC

Due to the limited amount of sand available for core 223BC intervals 11-12 cm and 31-32

cm, no smear slides were made. Point count data for core 223BC on intervals 20-21 cm and 15-

16 cm (the only two slides for core 223BC) show an overall decrease in rock fragments and

increase in quartz [relative to 249PC]. (Figs. 4-13, 4-14) Quartz abundances for core 223BC (22

% and 27 %) were at least twice that of those observed in core 249PC. The core 223BC interval

containing fewer rock fragments (15-16 cm) had a corresponding increase in quartz fragments

(27%). Biotite occurrence is at 4% for both intervals, while amphibole and accessory minerals

show a slight (1% to 2%) increase in the 15-16 cm segment.

Relative to core 249PC, core 223BC contains more quartz and fewer rock fragments, with

a more angular shape. Mineralogy of the fine-sized fraction is very similar between cores

(Figure 4-25). From XRD analysis, the most significant peak corresponds to quartz at 26.67 (at

26cU), and is noted again at secondary peaks (e.g., 50.21). The peaks corresponding to illite,

chlorite, and kaolinite are all elevated in core 249PC relative to core 223BC. This is expected









due to the higher percentage of clay in core 249PC relative to 223BC. Core 223BC contains one

additional mineral (likely a feldspar) which is not present at core 249PC.

Grain Size

Grain size separation shows an average of ~66% clay, ~26% silt, and ~8% sand for core

249PC from 0-30 cm, with specific intervals ranging from 57 % to 71 % clay. (Table 4-3) There

is an increase in silt with depth (22% to 31%), and an overall increase in sand (8% to 12%). The

core 249PC interval 21-30 cm shows a significant decrease in percent clay and increase in

percent sand (57% clay, 12% sand).

Grain size averages for core 223BC are 62% clay, 33% silt, and 3% sand, with clay

ranging from 58 % to 67 %. There is an overall slight decrease in percent clay with depth (67%

to 61%). Contrastingly, there is an overall slight increase of both percent silt (3 1% to 38%) and

percent sand (2% to 6%) with depth. The exceptions are interval 15-16 cm which exhibits a

slight decrease in percent silt from the interval above it, and interval 31-32 cm which exhibits

distinctly low sand content.











Table 4-1. Radionuclide concentration data and associated error of each bulk sample within each
interval .

23U (ppm) error 23Th (ppm) Error 4K (%) error
249PC
0-10Ocm 4.2 10.7 4.6 10.4 2.4 1.
11-21cm 4.3 10.7 4.7 10.4 2.4 1.
21-30cm 4.4 10.7 5.9 10.4 2.3 1.

223BC1
11-12cm 3.7 10.7 4.1 10.4 2 1.
15-16cm 3.2 10.7 3.4 10.4 1.8 1.
20-21 cm 2.4 10.7 0.6 10.4 0.3 1.
31-32cm 1.7 10.7 2.1 10.4 0.9 1.
Note: For core 249PC, the three bulk samples were averaged























































































^ 10

3


O
15






20






25



Figure 4-2. Concentration ofthorium with depth in core 249PC.


U (ppm)
10 20 30 40


50 60 70 80


~tt~H


5






S10






15






20






25


*0-10cm
11-20cm
21-30cm


Figure 4-1. Concentration of uranium with depth in core 249PC.


Th (ppm)
10 20 30 40


50 60 70 80


4 0-10cm
H 11-20cm
21-30cm























I
~t~tH












~t~HI


K (%)
15


Ob


10


20


2b


30


5






S10






15






20






25


0O-10cm
11-20cm
I21-30cm


Figure 4-3. Radioisotopic concentration of potassium with depth in core 249PC.


U (ppm)
05 10 15 20 25


30 35 40 45 50


5




10




E 15




20




25




30




35


I I




I r 1


+11-12cm
15-16cm
A20-21cm
X 31-32cm


Figure 4-4. Concentration of uranium with depth in core 223BC.


















Th (ppm)
05 10 15 20 25


30 35 40 45 50


5



10



S15



S20



25



30



35


I H I



I I


*11-12cm
15-16cm
20-21cm
X 31-32cm


Figure 4-5. Concentration of thorium with depth in core 223BC.


K (%)


5



10



S15



20



25



30



35


H [


*11-12cm
15-16cm
20-21cm
X 31-32cm


Figure 4-6. Concentration of potassium with depth in core 223BC.











Table 4-2. Specific concentrations of elements within each core
DEPTH 238U (ppm) 232Th (ppm) 40K (%)
CORE 249PC
249 PCa 0-10 cm 4.5 3.1 2.5
249 PCb 0-10 cm 4.0 5.8 2.3
249 PCc 0-10 cm 4.2 5.0 2.4

249 PCclay 0-10 cm 3.9 4.3 2.7
249 PCsilt 0-10 cm 4.4 6.0 1.7
249 PCsand 0-10 cm 3.1 3.6 1.8

249 PCa 10-20 cm 4.0 4.4 2.4
249 PCb 10-20 cm 4.3 4.3 2.4
249 PCc 10-20 cm 4.6 5.2 2.4

249 PCclay 10-20 cm 6.0 4.0 2.8
249 PCsilt 10-20 cm 4.2 4.3 2.2
249 PCsand 10-20 cm 3.5 5.9 1.5

249 PCa 20-30 cm 4.1 5.3 2.2
249 PCb 20-30 cm 5.0 5.8 2.3
249 PCc 20-30 cm 4.1 6.6 2.3

249 PCclay 20-30 cm 5.3 4.4 2.7
249 PCsilt 20-30 cm 3.8 4.2 1.4
249 PCsand 20-30 cm 3.9 4.0 1.6

CORE 223BC
223 BC 11-12 cm 3.7 4.1 2.0
223 BCclay 11-12 cm 0.1 4.2 1.2
223 BCsilt 11-12 cm 2.3 0.8 0.8
223 BCsand 11-12 cm N/A N/A N/A

223 BC 15-16 cm 3.2 3.4 1.8
223 BCclay 15-16 cm 2.0 2.6 1.7
223 BCsilt 15-16 cm 2.9 5.1 1.2
223 BCsand 15-16 cm 0.2 3.9 0.3

223 BC 20-21 cm 2.4 0.6 0.3
223 BCclay 20-21 cm 2.2 2.8 1.7
223 BCsilt 20-21 cm 3.9 4.0 1.2
223 BCsand 20-21 cm 3.2 4.9 0.8

223 BC 31-32 cm 1.7 2.1 0.9
223 BCclay 31-32 cm 3.2 3.7 2.1
223 BCsilt 31-32 cm 1.9 3.2 0.3
223 BCsand 31-32 cm 0.1 0.3 0.1


























9 249PC O-10
H 249PC 11-20
249PC 21-30
X 223BC 11-12
X 223BC 15-16
S223BC 20-21
+ 223BC 31-32


0% 10% 20% 30% 40% 50% 60% 70% 80%

% clay-sized material





Figure 4-7. Concentration of uranium with respect to percent clay for all intervals. After ~60%

clay-sized material, there is a general increase of uranium concentration with

increasing clay-sized material.


6249PC O-10
249PC 11-20
249PC 21-30
X 223BC 11-12
*223BC 15-16
e223BC 20-21
+223BC 31-32


0% 10% 20% 30% 40% 50% 60% 70% 80%

% clay-sized material



Figure 4-8. Concentration of thorium with respect to percent clay for all intervals.
























2 0



1 5




1 0


* 249PC 0-10
H 249PC 11-20
249PC 21-30
X 223BC 11-12
X 223BC 15-16
S223BC 20-21
+ 223BC 31-32


0% 10% 20% 30% 40% 50% 60% 70% 80%

% clay-sized material



Figure 4-9. Concentration of potassium with respect to percent clay for all intervals.

















2% 2% 1%





g rock frags
a quartz
O amphibole
O blotite
accessory


Figure 4-10. Mineralogy of sand fraction within core 249PC interval 0-10 cm.
































g rock frags
quartz
O amphibole
O blotite
accessory


Figure 4-11. Mineralogy of sand fraction within core 249PC interval 11-20 cm.


rock frags
quartz
O amphibole
O blotite
accessory


Figure 4-12. Mineralogy of sand fraction for core 249PC interval 21-30 cm.





























g rock frags
quartz
O amphibole
O blotite
accessory


27%


Figure 4-13. Mineralogy of sand fraction from core 223BC interval 15-16 cm.












3% 4% 2%


22%


g rock frags
quartz
O amphibole
O blotite
accessory


Figure 4-14. Mineralogy of sand fraction from core 223BC interval 20-21 cm.


























Figure 4-15. Typical image of core 249PC interval 0-10 cm showing mostly rock fragments
(designated RF) with associated quartz. Field of view approximately 0.8 mm.


Figure 4-16. Image of biogenic material (designated BM) among rock fragments in core 249PC
interval 11-20 cm. Field of view approximately 0.8 mm.



























Figure 4-17. Oxidized coating on grain from core 249PC interval 11-20 cm. This interval was
the only one exhibiting coated grains. Field of view approximately 1.25 mm.


Figure 4-18. Images of biotite (designated B) and accessory minerals from core 249PC interval
21-30 cm. Field of view approximately 1.25 mm.



























Figure 4-19. Typical picture of core 249PC interval 21-30 cm showing large rock fragments and
quartz (designated Q). Field of view approximately 1.25 mm.


Figure 4-20. Image from core 223BC interval 15-16 cm. Rock fragments dominate but there is
an increase in quartz and accessory minerals. Sand particles in this core are also more
angular in shape. Field of view approximately 1.5 mm.



























Figure 4-21. Typical image from core 223BC interval 15-16 showing elevated abundances of
plagioclase and amphibole, as well as increased quartz (relative to core 249PC)
among the dominant rock fragments. Field of view approximately 1.0 mm.


Figure 4-22. Image of core 223BC interval 15-16 cm silt fraction. Field of view approximately
1.5 mm.



























Figure 4-23. Image of biotite among rock fragments and quartz grains from core 223BC interval
20-21 cm. Field of view approximately 0.8 mm.


Figure 4-24. Image of core 223BC interval 20-21 cm silt fraction. The silt fragments are larger
in general size as compared to the 15-16 cm interval of this core. Field of view
approximately 1.5 mm.










































~~r11 I 'P''"""

1sZ~~l II ( II IFDIF~4~r







10 %& d 40; S1 ;60
2-Thela~dq)


123<507$90~ 1"" ~~1 a~~"l~'''""I"""" I '" ~~t"


-1








- 29P


-23B


Figure 4-25. XRD data for both cores with associated mineralogy. Core 249PC is offset (raised)
to better illustrate variations between cores.



















63










Table 4-3. Percent of clay-, silt- and sand-sized fractions from the two cores. The averages for
each core are included at the bottom.
Total % clay Total % Silt Total % Sand
249PC
0-10cm 70 22 8

11-20cm 71 25 4

21-30cm 57 31 12

223BC
11-12cm 67 31 2

15-16cm 66 30 4

20-21cm 58 36 6

31-32cm 61 39 0.3


Averages

249PC

223BC


Avg. clay %


Avg. silt %


Avg. sand %









CHAPTER 5
DISCUSSION

Grain Size

Core 249PC has a similar percentage of fine-sized sediment in the 0-10 and 1 1-20 cm

intervals, with a decrease in sand due to a slight (1% and 3%) increase in clay and silt. The 21-

30 cm interval exhibits a significant drop in clay and increase in sand from the two intervals

above it. This influx of sand can be attributed to the 1964 earthquake, which corresponds to that

interval given the sediment accumulation rate (~1 cm y^l, Jaeger et al. 1998). The earthquake

epicenter was located in nearby Prince William Sound and accounted for extensive redistribution

of sediments by tsunamis (Jaeger et al. 1998).

Sand percentage at core 223BC increases steadily downcore (2%, 4%, and 6%) until the

31-32 cm interval where it drops to 0.3 %. Due to the extremely high sedimentation rate in the

northern Icy Bay location (>0.3 cm d- Jaeger 2002) and lack of steady-state deposition,

inconsistencies with accumulation and grain size at depth are expected. Decreased sand could be

attributed to increased precipitation, which may substantially increase meltwater discharge and

associated velocity, and allow for deposition of the sand-sized fraction further from the glacial

termimi.

The two sites reveal variations in transport environments, which may affect grain size

distribution. The presence of a moraine and Bear Lake between Bear Glacier and the

Resurrection Bay core 249PC site may act as a trap for grains silt-sized and larger, whereas

Guyot Glacier is a tidewater glacier, which deposits sediment directly into Icy Bay (Figs 2-1, 2-

2). This may also explain the lower relative clay percentages in core 223BC compared to core

249PC. Guyot Glacier is connected to the water body and contributes sediment directly into Icy

Bay, allowing for extended suspension and distribution of the finer particles.










Composition

Mineralogy of the two cores is surprisingly similar. Both cores are from a temperate

glacial environment in the GOA, which produces predominantly glacimarine rock flour,

therefore, a general similarity in particle size and common rock-forming mineralogy (relative to

other parts of the world) is expected. The almost identical results from both petrographic and

XRD analyses are not expected based on differing source lithology and geological environments

(Figs. 1-2, 1-3). The XRD patterns, when viewed together, are distinguished only by more well-

defined peaks from the Icy Bay sample, and one or two additional minerals (likely feldspars,

McClellan, verbal communication) at the same site (Figure 4-25). Differences in peak intensities

are partly due to variations in clay mineralogy as well as increased overall clay percentage in the

249PC sample. Higher proportions of clay-sized particles produce a less intense, muted

appearance in graphs (Moore and Reynolds 1997). The mineralogic analyses (4-10 through 4-

14) show nearly identical sediment compositions, even with regard to accessory minerals. The

variation is principally in relative percentages, the exception being the increase in biogenic

material under accessory minerals in core 249PC interval 11-20 cm. These findings indicating

that the source rocks presented in the two core sites may not be as different as initially thought.

No source has currently been determined for the Yakataga Formation. It is possible that the

Chugach terrane, which is the source material for core 249PC sediments, is also the source for

the Yakataga Formation sediments of core 223BC.

The point count data for core 249PC shows an overall decrease in rock fragments with

depth, and a slight elevation in amphibole, biotite, and accessory minerals for intervals 11-20 cm

and 21-30 cm. The coarse-size fraction of both cores contains predominantly rock fragments,

with the next most common occurrence being quartz (though core 223BC consists of nearly

twice the quartz of core 249PC). Both cores also contain biotite, amphibole, and accessory









minerals in amounts of less than 5 percent. The weathering of differing source rock types

surrounding each basin should hypothetically produce differing clay-mineral percentages (Hein

et al. 2003). Though relative clay-mineral percentages vary between the cores, it is only a slight

variation which can be attributed to differences in sedimentation processes between core sites, or

seasonal sediment discharge fluctuations. Elevated illite content at the Resurrection Bay area

relative to the Icy Bay area seen in the XRD analysis was also recorded by Molnia and Hein

(1982). A single depositional or periodic event might alter source of sediment, and is a possible

reason for elevated illite (e.g., flooding at an illite-rich drainage basin or rapid draining of a

lake).

Elemental Concentrations

Elemental concentrations are predominantly due to mineralogy, diagentic changes of clay

mineralogy, and adsorption processes (Ayres and Theilen 2001). Elevated clay mineral contents

(illite, chlorite) and overall clay-sized material percentages in core 249PC (Figure 4-25, Table 4-

3) correspond to higher isotopic concentrations. Radioactivity is often associated with clay- or

fine-sized particles (van Wijngaarden et al. 2002, Anderson 2004, Naidu, Han, Mowatt, and

Wajda 1995). Relatively high concentrations of K have been recorded in marine sedimentary

rocks of the Valdez Group near Bear Glacier (Goldfarb and Borden 1982). The Aialik pluton

outcrops discontinuously around the mouth of Resurrection Bay, it is locally biotite-rich and may

contribute to increased potassium levels (Kusky, Bradley, Donley, Rowley, Haeussler 2003).

In an attempt to better represent elemental concentrations, samples from this study were

normalized to percent clay. (Table 3-2) Due to the high amount of clay initially in most of the

intervals, relative concentrations of normalized data are similar to initial bulk concentration data,

with an increase in specific concentrations. Core 249PC interval 21-30 cm has a high elemental

concentration (in each of the three elements) with respect to the relatively low sand percentage










(Figs 4-7 through 4-9). This may be due to the catastrophic nature of the 1964 earthquake event

that deposited the sediment. Material of a wide range of sizes was moved at an extremely rapid

rate, which would allow for minimal disaggregating of clay particles before deposition and

burial.

238U

Though the averaged concentrations for uranium in core 249PC show an increase in

activity with depth, it is not definitive. (Figure 4-1, Table 4-2). Based on the concentration data

and associated errors (Figure 4-1), it is impossible to conclude there exists an increased uranium

concentration with depth. There is, however, a general consistency of uranium elemental

concentration in all intervals from core 249PC, even at the 21-30 cm interval, which contains

considerably less clay. By analyzing a homogenized 10 cm sample, as was done for core 249PC,

fluctuations in sedimentation could be minimized, producing more consistent results.

The uranium concentrations in core 223BC decrease with depth in an almost linear

manner. The decrease in concentration corresponds to a decrease in clay and, therefore, supports

the correlation of activity of this element with grain-size. At the 20-21 cm interval uranium is

elevated relative to thorium (Tables 4-1, 4-2). This interval is the most similar to the hypothesis

put forth regarding an increase in uranium with associated decrease in potassium and thorium,

and is the only interval where this behavior is seen. The hypothesis stated this might be due to

heavy minerals concentrated in the sand fraction. Based on the mineralogy observed in this

study that conclusion is unlikely.

232Th

Core 249PC shows an increase in the average concentration of thorium with depth. When

errors are taken into account (Figure 4-2) the increase becomes unclear. This results in thorium

exhibiting a general consistency in elemental concentration among all intervals, much like the









uranium concentration in this core. There is an increase in silt content (Table 4-3) with depth

that may support the association of thorium with the silt-sized fraction. Due to lack of

consistency, it is more accurate to associate thorium with the more general fine-sized fraction

(<63 Cpm) than to specify either the clay- or silt-sized fraction. Thorium elemental abundance in

core 223BC shows the same general decrease with depth as seen with uranium, except at the 20-

21 cm interval where concentration significantly lower than the other intervals. Thorium

abundance in both cores is higher than uranium abundance, and can be related to initial

mineralogy, since thorium is more abundant in the earth (10ppm) than uranium (2ppm) (Ruffell

and Worden 1999). This interval exhibits the highest amount of sand (6 %) within the core,

supporting the association of the fine-sized fraction with thorium elemental concentration. The

elevated thorium concentration relative to uranium at both the Resurrection Bay and Icy Bay

core sites is also seen in published geochemical data. (Figs. 1-4 through 1-6)

4oK

The percentage of potassium in core 249PC fluctuates very little (<1 %) and, therefore,

does not specifically show a decrease with depth. Potassium concentration only varies by 0.1%

in each of the three intervals in the 249PC core. The concentration is highest in the clay fraction

and lowest in the sand fraction at every interval. The consistency seen in potassium elemental

abundance among samples for core 249PC is similar to uranium and thorium. The sediment

associated with core 249PC shows slightly elevated overall concentrations of all radioisotopes

examined when compared to core 223BC, but is particularly noticeable with potassium.

Core 223BC potassium concentrations range from 0.3 % (20-21 cm interval) to 2.0 % (11-

12 cm interval). Core 223BC shows an overall decrease in potassium with depth, similar to the

uranium and thorium concentration with depth seen in this core. The exception is a very low









concentration at the 20-21 cm interval which corresponds to the lowest amount of clay (58 %)

and highest amount of sand (6 %) in the core.

There is an obvious association of potassium with the clay fraction for both cores. Glacial

meltwater is known to be relatively high in potassium (Anderson 2004). Sediment discharged

into the GOA is predominantly clay-sized and thus is the principal potassium source, since

potassium is locked in the clay mineral lattice and relatively immobile. Physical grinding of

biotite grains during abrasion in this type of glacial environment also exposes the inner layer

(potassium) cations (Anderson 2004). The release of potassium relative to plagioclase is

promoted in colder climates due to this type of biotite weathering (White et al. 1999; Blum and

Erel 1997) and thus contributes to overall potassium. The potassium radioisotope is spread

through many rock-forming minerals (e.g., feldspar) as well as heavy minerals (Asadov,

Krofcheck, and Gregory 2001), so a uniform signal even after separation into size fractions is not

uncommon.

In general, core 249PC exhibits a different (elevated) elemental abundance from that of

core 223BC, particularly when normalized to mass percent clay (Table 3-2). The distinction can

be associated with an elevated percentage of clay-sized grains at core 249PC (Table 4-3), since

there is an association of concentration with the fine-sized fraction. Note that the low sand

content in the 11-20 cm interval does not result in a low uranium concentration or elevated

thorium and potassium. A higher accessory mineral content was recorded for this interval, but

was largely due to increased diatom tests and biogenic material. The initial hypothesis suggested

that 238U (uranium) in the cores was associated with zircons or other heavy minerals which are

resistant to weathering and, therefore, concentrated predominantly in the coarse (>63 Clm)

fraction, and that 232Th (thorium) and 40K potassiumu) are associated with clays (illite, chlorite)









and mica. Uranium abundances are similar to thorium and potassium abundances at almost

every interval. The intensity of the glacial abrasion can promote the release of dissolved

uranium from rocks into the waters where it would be incorporated into the fine-sized fractions

(Taboada, Cortizas, Garcia, and Garcia-Rodeja 2006; Hodson 2002).

The decrease in percent clay at the core 223BC 20-21 cm interval is a likely explanation

for lower 232Th and 40K activities. Gamma-ray activity should be a function of grain size

(Asadov et al. 2001), and appears to be recorded here. With regard to potassium in particular,

there seems to be an association with the fine-sized fraction, (the dominant sediment mode in the

GOA), and the clay-sized fraction specifically. Changes in clay mineralogy (decrease in

potassium-rich illite clay relative to smeetite clays) are thus likely responsible for decreasing

natural gamma activities not associated with decrease in clay-sized sediments.

Clay Mineralogy

Clay mineral assemblages play an intricate role in controlling radioactivity and are

particularly informative of source rock composition (Naidu et al. 1995). This is primarily due to

the fine-sized fraction comprising the maj ority of sediment discharged in the GOA and the

association of potassium with this fraction (Jaeger et al. 1998; Molnia and Hein 1982; Anderson

2004). Clays in the GOA are characterized by high amounts of illite and chlorite with traces of

expandable clay minerals and little to no kaolinite (Naidu et al. 1995; Molnia and Hein 1982).

Based on XRD in this study there is a presence of kaolinite that is considered to be high relative

to previous studies. This is attributed to kaolinite having a tendency to flocculate and

concentrate in shallow marine successions close to shore (Ruffell and Worden 1999). Kaolinite

and expandable clays such as montmorillanite contain significantly less potassium (and thorium)

relative to illite clays (Ayers and Theilen 2001; Ruffell and Worden 1999). Thus, if a decrease

in the relative abundance of an element (e.g., potassium) does not coincide with a significant









decrease in the fine-sized fraction, it may simply be related to the clay minerals present, as well

as the mineralogy of non-clay minerals in the clay-sized fraction.

Th/K Ratios

It is suggested that the mobility of potassium and uranium and the relative concentration of

thorium during weathering should result in clays with elevated Th/K and Th/U ratios (Schnyder

et al. 2005). The Th/K ratio is used to recognize clay mineral, feldspar, and mica associations

(Ruffell and Worden 1999). Clay mineral analyses and Th/K ratios help to distinguish long-term

transgressive events as well as short-term flooding (Ruffell and Worden 1999). When these

ratios are plotted, core 249PC exhibits a mix of chlorite and illite, with most points falling close

to each other due to the very consistent potassium concentration. (Figs 5-1 through 5-3) Core

223BC shows a very consistent ratio of 2:1 for thorium and potassium. Core 223BC interval 20-

21 cm records the lowest concentration of both thorium and potassium. When the Th/K ratio is

plotted against percent clay, there is little distinction between the two cores. (Figure 5-4) The

similarity of clay mineral percentages, as well as depositional processes would produce similar

Th/K ratios once normalized to clay.

Possible Alteration/Biasing of Signal

It is important for this study to understand the potential extent of chemical weathering in

the glacial environment, particularly for this type of study, which assumes initial source material

is represented accurately in the sedimentary record. The geochemistry of a sedimentary deposit

is often influenced by many variables other than parent rock composition (Fralick 2003).

Weathering can be the dominant process affecting the geochemistry of sedimentary rocks, and

physical weathering is the dominant process in glacial environments. Mobility of elements is

particularly hard to constrain in these types of cold weather environments. Uplift and erosion are

actively occurring in the GOA, and they are a driving function for geochemical cycling.









Additionally, runoff and temperature are two of the most important parameters controlling

chemical weathering rates (Dessert, Dupre, Gaillardet, Francois, and Claude 2003; Derry and

France-Lanord 1996). The nature of the temperate glaciers within the study area makes chemical

alteration a possibility relative to colder climates due to the presence of water at the glacier base.

This allows the glacier to erode its bed and thus provides conditions necessary for accelerated

weathering (Anderson, Drever, Frost, and Holden 1999).

The potential of a difference in uranium concentration between parent-rock and sediment

deposited is greater than that of thorium or potassium in this type of environment (Ruffell and

Worden 1999). Conditions on the southern Alaska margin are considered oxidizing and there is

very little organic matter present. Under sufficiently oxidizing conditions uranium is commonly

soluble in water (as U+6), while thorium has low solubility (Faure 1986). The mineralogy of the

sand fraction did not reveal heavy minerals typically associated with uranium and therefore must

be broken down prior to deposition and incorporated into all size fractions. This even

distribution could occur by dissolved uranium in the water column being transported in

proglacial rivers and streams. Thorium and potassium are both considered to be locked in the

mineral lattice, and relatively immobile. The exception is thorium, which may be somewhat

mobile in the water column.

The GOA is considered an oxidizing environment, it is likely that reducing conditions

would exist only after deposition. Post-depositional alterations are very unlikely considering the

rapid accumulation of sediment at each site, and relatively short time-period represented in each

core. Previous studies show that glacial meltwater is likely the dominant factor governing

elemental fluxes (White and Blum 1995; Anderson 2004). There are englacial and supraglacial

flow paths transmitting water quickly to outlet streams, allowing little opportunity to interact









with rocks and sediments (Anderson et al. 1999; Collins 1979). Mountain ranges in very close

proximity to the sea such as in southern Alaska minimize terrestrial storage, and sediments

within the Gulf have previously been characterized as having undergone mild chemical

weathering (Jaeger et al. 2001; Anderson 2004). Alteration is possible, but considered unlikely

and very mild given the extremely high discharge rates.

Correlation with Aeroradiometric Data

Aerial gamma-ray surveys measure the flux of gamma-rays emitted by the radioactive

decay of the elements 40K potassiumum, 238U (uranium), and 232Th (thorium). These elemental

abundances can be used as proxies for studies, because different rocks and soils generally

contain different amounts of these elements. Thus the aeroradiometric measurements obtained

can be useful for locating intrusive rocks and mapping rock units with a distinctive radioelement

signature (Duval, Cook, and Adams 1971). The National Uranium Resource Evaluation (NURE)

program was conducted by the U.S. Government to assess radioelement data (Duval 2001). The

program included airborne gamma-ray spectrometry and magnetic data collection along with

extensive geochemical sample collection and processing. Aeroradiometric surveys of 98 10 by

30 quadrangles were flown in Alaska between 1975 and 1980. The data, collected in 15 surveys

flown approximately 400 feet high and spaced approximately 6 miles apart, were done by Texas

Instruments (T.I.), Lockwood, Kessler and Bartlett (LKB), and AeroServices (Aero) under

contract with the U.S. Government. The surveys typically penetrate the upper 2 feet (Duval et al.

1971).

There is little correlation with aeroradiometric data in this study. (Figure 1-7) Elevated

uranium measured in sediments at the Resurrection Bay site (relative to Icy Bay) are not depicted

on the aeroradiometric map. There is a small area on the survey map near Resurrection Bay

which shows the presence of uranium, though it would not seem to be enough to influence the










elevated concentration recorded in the sediment here, particularly when compared with those of

the Icy Bay core. The aeroradiometric survey map shows an absence of thorium in the Icy Bay

environment with a highly elevated uranium concentration, also not recorded in the measured

data.

One possible explanation for the elevated uranium concentration near Icy Bay on the

aeroradiometric map is the preferential sorting of heavy minerals by aeolian transport processes.

Aeolian transport has been shown to be effective at zircon enrichment and produce very high Zr

and Hf contents in loess deposits when compared to continental crust (Taylor 1983; McLennan et

al. 2003). These zircon enrichments on the surface near the Icy Bay environment would cause

elevated uranium unrelated to parent rock material or the coarse fraction. There might also be

biases in the aeroradiometric map due to extrapolation of data. The 6-mile spacing between

flight-lines would require assumptions to be made about the areas not directly measured. The

analysis then is that there is no overall correlation of aeroradiometric maps with measured

concentrations, and they should not be used for comparison with core material in the southern

Alaska environment.

Correlation with Geochemical Data

Geochemical data from river and stream samples (Figs. 1-4 through 1-6) reveal very

similar elemental abundances to those determined at the core sites. The thorium data suggest a

concentration at both core locations with a range from <3.7 to 8.7 ppm. (Table 4-1) Thorium

concentrations were slightly lower at core 223BC relative to core 249PC, but still fall within

published ranges. Potassium concentrations of both published data and that of this study show

elevated concentrations in the core 249PC environment relative to those at core 223BC.

Uranium is also slightly elevated in both this study and published data at the 249PC site. Core

223BC published data suggests a concentration ranging from approximately 1.4 to 3.8 ppm,









which is very close to what this study observed. The environment near core 249PC shows a

range of 1.9 to 7.3 ppm in published data, which is also almost identical to what was observed in

this study. Though the ranges for core 223BC are large relative to 249PC ranges, they are well

within the concentrations of published geochemical data.












































s


5

X


=10 0


80


60


40


20


00


* 249Pc 0-10cm
S249Pc 11-20cm
249PC 21-30cm


00 05 10 15 20 25 30 35 40 45 50
K (% )


Figure 5-1. Th/K ratio from core 249PC.


20 0


18 0


16 0


14 0


12 0


=10 0


80


60


40


20


00


4 223BC 11-12cm
S223BC 15-16cm
223BC 20-21cm
X 223BC 31-32cm


00 05 10 15 20 25 30 35 40 45 50
K (% )


Figure 5-2. Th/K ratio for core 223BC.

















kaolinite/sete

16.0 Mixed layep



illite



12.0







0.0


v
)K


0 0.5


1.0 1.5 2.0


3.5 4.0


K (%)

Figure 5-3. Overlay of Th/K ratio for both cores


S249PC 0-10cm
H 249PC 11-20cm
249PC 21-30cm
X 223 BC 11-12cm
m 223BC 15-16cm
e223BC 20-21cm
+ 223BC 31-32cm


0 10 20 30 40
% clay


50 60 70 80


Figure 5-4. Th/K ratio with percent clay for cores 223BC and 249PC showing little variation
between them.


223BC


g 249PC,









CHAPTER 6
CONCLUSION

The hypothesis stated previously was that 238U was associated with zircons or other heavy

minerals carried predominantly in the coarse (>63 Cm) fraction, and that 232Th and 40K were

associated with clays (illite, chlorite) and mica in the fine-sized fraction. This was expected to

produce an elevated 238U concentration in core 223BC, and an elevated 232Th and 40K

concentration at core 249PC, since 249PC contains more fine-grained material. Though 249PC

did show elevated 232Th and 40K concentrations due to a higher clay percentage, the 238U was

also increased. This is indicative of the 238U radioisotope also being carried predominantly in the

fine-sized fraction.

This study shows no correlation between concentration and the sand-sized fraction. The

sand fraction has been shown to display a wide range of radioactivity and often produces results

similar to those in this study (Blum and Erel 1997; Ayers and Theilen 2001). The variability of

238U and 232Th with each interval makes it difficult to discern precisely where it is being carried,

though it is can be generally associated with the fine-sized fraction. There is particularly good

association of the 40K radioisotope with the clay-sized fraction, it is highest there for each

interval of both cores. Natural gamma activity in this study is thus controlled primarily by grain

size and not mineralogy, though clay mineral assemblages do play a role in determining relative

amounts of potassium. Previous studies have determined that the radioactivity from potassium

often dominates the natural activity of the sediment and can be used as a provenance tool (Ayers

and Theilen 2001).

The second part of the hypothesis suggested that if grain size did play a role in controlling

radioisotopic activities, then it could be possible to determine provenance based on the

radioisotope analysis of each core. Though grain size does show a strong correlation with










potassium, the similar overall clay percentage and mineralogy of the two cores make a distinct

provenance determination difficult. Overall concentrations of core 249PC are higher than those

of core 223BC are therefore distinguishable, but not convincingly. It is very possible that the

Chugach terrane associated with the Chugach and St. Elias Mountains is influencing the source

material at both locations, thus disrupting the unique geological terrane characteristics. This

would imply that the Valdez group and the Yakataga formation are composed of material from

the Chugach terrane. Specific determination source material for the Yakataga formation is

beyond the scope of this thesis, however, the similarity in XRD and petrographic analyses

supports a more similar source material than originally estimated. The slightly elevated

radioactivity at core 249PC is then attributed to a combination of elevated fine-sized sediment

and slightly elevated initial potassium content of the rock assemblages near Bear Glacier and

Resurrection Bay.

A secondary goal of the study was to test the validity of aeroradiometric data from the

southern Alaska region. The noticeably high uranium in core 223BC relative to 249PC

illustrated in Figure 1-7 was not seen. This is likely due to the misrepresentation of parent rock

material by aeroradiometric data. The high uranium levels recorded are attributed to

concentrated near-surface coarse material deposition both by receding glacial activity and

aeolian processes. This would concentrate heavy minerals that weren't incorporated into the

finer fraction (such as zircons and monazite) in the coarse fraction while the fine-sized fraction

was transported to the Gulf. Certain storm-induced flooding resulting in high sediment discharge

will still carry some heavy minerals to the Gulf (possibly recorded in core 223BC interval 20-21

cm), however would not be significant enough to prevent a bias in aeroradiometric

measurements at certain depositional environments. Inferring sediment provenance from the









final product is anything but straightforward since it evolves as it is transported from the source,

this affects the near-surface sediments measured by the aeroradiometric surveys in particular

(Weltje and Eynatten 2004).

This study shows that, in general, there is a correlation of radioisotope activity with grain

size. The inconsistencies observed reveal there are other factors, such as mineralogy and surface

adsorption (particularly for 232Th), contributing to overall activity. Activity of the 40K isotope is

the least affected by factors other than grain size, and correlates well with the amount of clay-

sized material. The similarity of source mineralogy makes distinction between locations

difficult. Results do show a slight distinction the two cores, and thus it may be possible to use

this technique for provenance determination between two more unique environments. Th/K

ratios are consistently near 2: 1 at core 223BC, whereas the ratio at core 249PC is variable. Also,

the minimum 40K values of core 249PC are higher than the maximum ones at 223BC. Natural

gamma activity in this study is then primarily controlled by amount of clay minerals and the

potassium content of the clay mineral assemblages, which has been recorded in other studies

(Ayres and Theilen 2001; Carter and Gammon 2004). Naturally it would be ideal to apply a

suite of current techniques to obtain the highest accuracy and precision for provenance

determination. These techniques can be very time consuming and expensive. Geochemical data

from stream and river samples (Weaver 1983) for the GOA margin correlates well with

radioisotopic concentrations measured in this study, proving that it is a non-destructive and

efficient way of accurately determining radioisotope concentration. Given two more unique

environments, this technique could be a very valuable provenance tool.










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BIOGRAPHICAL SKETCH

Alice Hildick was born in Vermont on February 16, 1979. She grew up in Florida, where

she graduated from Clearwater Central Catholic High School. She got her bachelor' s degree in

geology from the University of Florida in 2001, worked for Geohazards, Inc., then returned to

the University of Florida to get her Master of Science degree. She spent time working at

GeoSierra, LLC in Atlanta for a brief period during her Masters research. Alice' s favorite things

include traveling, surfing, and wine.