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Stratigraphic correlation of outcrop gamma ray profiles in Florida ( FGS: Open file report 26 )
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 Material Information
Title: Stratigraphic correlation of outcrop gamma ray profiles in Florida ( FGS: Open file report 26 )
Series Title: ( FGS: Open file report 26 )
Physical Description: 1 v.(unpaged) : ill., maps ; 28 cm.
Language: English
Creator: Johnson, Richard A ( Richard Alan ), 1949-
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee Fla
Publication Date: 1989
 Subjects
Subjects / Keywords: Geology -- Florida   ( lcsh )
Stratigraphic correlation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Richard A. Johnson.
Bibliography: Includes bibliographical references.
General Note: Cover title.
 Record Information
Source Institution: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: aleph - 001545483
oclc - 22438939
notis - AHF9003
System ID: UF00001025:00001

Table of Contents
    Main
        Main
    Front Cover
        Front Cover 1
        Front Cover 2
    Title Page
        Title Page
    Abstract
        Page 1
    Stratigraphic correlation of outcrop
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
    References
        Page 27
Full Text






FLRD GEOLOSk ( IC SUfRiW


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State of Florida
Department of Natural Resources
Tom Gardner, Executive Director




Division of Resource Management
Jeremy Craft, Director




Florida Geological Survey
Walt Schmidt, State Geologist and Chief









Open File Report 26


Stratigraphic Correlation of Outcrop
Gamma Ray Profiles in Florida

by

Richard A. Johnson


Florida Geological Survey
Tallahassee, Florida
1989























3 1262 04543 6218



k9
'f





fusor











State of Florida
Department of Natural Resources
,,Tom Gardner ,.Executive Director

Division of Resource Management
Jeremy Craft, Director


Florida Geological Survey
Walt Schmidt, State Geologist and Chief





Open File Report 26

Stratigraphic Correlation of Outcrop

Gamma Ray Profiles in Florida

by

Richard A. Johnson


Florida Geological Survey
Tallahassee, Florida
1989


Florida Geological Survey
Library
903 West Tennessee Street
Tallahassee, Florida 32304





ABSTRACT


Stratigraphic Correlation of Outcrop Gamma Ray
Profiles in Florida. R.A. JOHNSON, Florida Geological Survey,
903 W. TennesseeStreet, Tallahassee, 32304. Utilizing a hand-
held scintil1ometer, total count gamma ray profiles were run on
outcrops exposing many different lithologies in Florida.
Emphasis was placed upon those outcrops which exhibited one or
more stratigraphic contacts in order to determine if changes in
the gamma ray signature could be relatedtd with formational as
well as lithologic changes. Since the lithologies present in
each outcrop were already known from a previous detailed study,
correlation of these lithologies with gamma ray response on a
bed-by-bed basis allowed detailed comparisons of typical
formation lithologies with total count gamma ray response. The
outcrop gamma ray profiles were then correlated with subsurface
borehole gamma ray logs to determine if specific lithologic
entities (beds) or stratigraphic units (formations, members)
could be identified in the subsurface more accurately using this
technique.
















NOTE

This Open File Report consists of the transcription in its entirety
of a paper presented at the Florida Academy of Sciences Annual Meet-
ing, April 1, 1989, at Florida Community College at Jacksonville,
Jacksonville, Florida.






STRATIGRAPHIC CORRELATION OF OUTCROP

GAMMA RAY PROFILES IN FLORIDA

In the 1970s and 1980s, the use of borehole geophysical logs

for stratigraphic correlation has been widespread in Florida.

Many governmental organizations and private consultants have been

involved with well logging, with the result that there are

currently an abundance of borehole geophysical logs available

across the state. However, until 1988, no outcrop gamma ray

profiles were available for any location in Florida. This

technique involves recording average gamma ray activity in

counts-per-second at intervals vertically acrosamanroutcrop,. c:

plotting these intensity readings versus height or depth; then

connecting the points (Ettensohn et al., 1979; Chamberlain,

1984). The result is, in essence, a gamma ray log of the outcrop

which can then be compared to borehole gamma ray logs. This

technique has been used in the oil industry for some time

(Ettensohn et al., 1979) but the first use of the technique

reported in the literature was in the paper mentioned above

(Ettensohn et al., 1979). The technique was also applied to the

thick sections exposed in the southwest by Chamberlain (1984).

This technique is therefore essentially new.

This study was begun in order to determine if outcrop gamma

ray profiles could be constructed from Florida outcrops and, if

so, whether the profiles could be correlated with borehole gamma

ray logs. The hand-held scintillometer used in this study

incorporates a very large 7.5 cubic inch thallium-

activated sodium iodide sensing crystal which is linked to a







photomultiplier tube to form a large and sensitive gamma ray

detector. Amplification and counting circuitry then covert the

signal into a standardized counts-per-second digital readout

which is averaged over 10 seconds in 2 second intervals of

counting time. The most sensitive borehole gamma ray probe

currently in use in the state uses a sensing crystal with a

volume of approximately 3.1 cubic inches, less than half the

volume of this hand-held scintillometer crystal. Since the

sensitivity of the scintillometer to gamma rays is directly

related to its crystal volume (Keys and MacCary, 1971) as well as

to other lesser variables, the very large crystal in the hand-

held scintillometer utilized in this study provided extremely

sensitive gamma ray counts. The scintillometer was placed

directly upon and in full contact with the bed being measured and

the readings were taken. This technique eliminates the borehole

gamma ray log variables of both changing borehole size and the

effects of probe movement from the outcrop gamma ray profiles

thus obtained.

At each bed or measuring station, between 3 and 5 10-second

readings were taken and the arithmetic mean of the readings was

recorded. Vertically across each outcrop, a spatial sampling

interval of 1 foot was used, unless the section contained beds

less than 1 foot in thickness. In that case, readings were taken

and averaged from the middle of each thin bed, at less than 1

foot intervals.

In the office, these data points were plotted versus height







at standardized scales adjacent to a standardized section diagram

showing bed lithology, thickness and weathering profile (Figure

1). The points were then connected, resulting in an outcrop

gamma ray profile similar to borehole gamma ray logs. One

difference between the profiles and gamma ray logs is scale. The
outcrop profile is recorded at a much-expanded scale vertically

and is much more sensitive to relative changes in count rate due
to the large crystal size. Another difference between the two is

that the borehole gamma ray log is recorded continuously over the

interval being logged, whereas the profile is constructed from

discrete points measured over the interval.

The gamma ray profile can thus be correlated directly with

exposed outcrop lithology. Peak-and-valley patterns in the

profiles can then be correlated with patterns seen in the
borehole gamma ray logs.

Gamma ray profiles from 49 outcrops across the state (Figure

2) were made for this study. Emphasis was placed upon relatively

thick continuous exposures and upon exposures which contained one

or more stratigraphic contacts between formations or members.

The profiles were correlated with borehole geophysical logs run

in the same local areas and in other areas of the state.

It was found that the suites of known lithologies which

compose formations as seen in outcrop were indeed correlatable as

a distinct series of formational patterns between outcrop gamma

ray profiles and borehole gamma ray logs. In addition, use of

type outcrop profiles and profiles which included a formational

contact allowed determination of typical gamma ray patterns for








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120 140 160 180 200 22

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UNDIFFERENTIATED


ST. MARKS


.1* .'a .

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CHATTAHOOCHEE
i I I I i


Figure 1.


Typical standardized section
gamma ray profile.


diagram and outcrop


0 240 260


I I






















































FLORIDA

(aldMtiM


a .


Figure 2. Locations of sections with outcrop
a -amma gay profiles.








each formation, which could then be recognized more easily in the

subsurface between borehole gamma ray logs.

Figure 3 shows a typical outcrop gamma ray profile and

section diagram of a quarry located in the panhandle of Florida

in Jackson County, northwest of.Marianna,. where the Ocala-

Marianna and Marianna-Suwannee contacts are both exposed. The

entire thickness of Marianna is exhibited at this quarry. The

gamma ray profile shows relatively high count rate intensity in

the uppermost undifferentiated siliciclastics; moderate intensity

peaks and valleys in the impure dolostone of the Suwannee; and a

relatively low count rate in the glauconitic but relatively pure

Marianna limestone. Near the top of the Marianna are two

moderately low intensity peaks which correspond to two thin but

widespread dolostone or dolomitic limestone beds separated and

overlain by hard, recrystallized, fine-grained, Marianna

limestone beds. The Ocala-Marianna contact near the base of the

section is recorded as a very low counts-per-second valley at a

bed of very hard, recrystallized, glauconitic, Lepidocvclina-sp.

-rich limestone which marks the top of the much-coarser-grained

Ocala.

Figure 4 shows an outcrop approximately 1 mile northwest of

this last quarry which better illustrates the typical panhandle

Ocala-Marianna contact. Here, the upper bed in the Ocala is that

same Ledidocyclina-sp.-rich, coarse grained, very hard limestone

bed as seen in Figure 3, with a very thin, soft, highly

glauconitic, calciruditic bed just below it. These two beds mark








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JACKSON CO.


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UNDIFFERENTIATED










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MARIANNA

























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Figure 4.


CPS 80


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JACKSON CO.
100 120. .140-


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MARIANNA


OCALA


.1


Section diagram and ga1ma ray Irofile of a1 outcrop 1
shown In FiFur. 3..


mile northwest


160
* i


180
































Sthe quarry
of the quarry


I -







the top of the Ocala in this area. The Marianna, above, is a

much finer-grained limestone, a calcilutite. The contact

exhibits a moderately high counts-per-second gamma ray peak just

below the contact, probably due to the high glauconite content.

This peak can be seen on many borehole gamma ray logs in the
area, as shown on Figure 5 in a log from a well about 3 miles

south southwest of Marianna (run by Northwest Florida Water

Management District). Figure 5 also shows the moderately high

counts-per-second dolostone pattern near the top of the well,

which is characteristic of the Chattahoochee, followed downward

by-the-lower, uneven trace characteristic of .he::Swaannje. .The-..

top of the Marianna is shown as a decrease in intensity. The

Ocala can be seen in this figure to be divisible into an upper,

slightly higher intensity zone, and a lower, slightly lower

intensity zone. Figure 6 shows this characteristic on an outcrop

gamma ray profile. This illustrates the outcrop gamma ray

profile and section diagram of a sinkhole to the northeast of

Marianna where the top portion of the Ocala is exposed. Below
the thin, undifferentiated siliciclastics is a thickness of 50

feet of calciruditic, Lepidocvclina-sp.-rich, limestone which can

also be divided into 2 zones on the gamma ray profile. The upper

zone is characterized by moderately high counts-per-second, with

a very low intensity valley at the top. The lower zone shows the

more characteristic very low, even intensity typical of the Ocala

elsewhere in the state. The upper portion is composed of very

porous, soft, slightly glauconitic, Lepidocvclina-sp.-rich

calcirudite which has been extensively infiltrated by clay washed


L I













Figure 5. Borehole gamma ray log run in a well south-
southwest of Marianna.













INCREASING CPS ,*


CHATTAHOOCHEE


SUWANNEE





MARIANNA










OCALA


'











I ,
a~


~REENWOD sOi ,, so

SINK

UNDIFFERENTIATED


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U _j I i i i i I I I II i i


120 14' 1S # @ C
___ CPS


1.AL


Figure 6. Section diagram and gamma ray profile of a sinkhole to
the northeast of Marianna.


5s


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tCj.^ ^ ^ ^^ ^ ^ ^ ^


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in through the very high intergranular and moldic porosity. This

clay, along with glauconite, is probably responsible for the

upper-Ocala, higher counts-per-second zone on the gamma ray

profile. Lithologically, the lower zone is composed of much-

lower-porosity, massive, very hard, recrystallized

LeDidocvclina-sp.-rich calcirudite, and shows the typical very
low intensity gamma ray trace characteristic of the Ocala

statewide. The top of this section of limestone as shown on this

gamma ray profile matches exactly the trace seen on the two last

figures at the top of the Ocala; that is, a very low counts-per-

second valley .just above a slight but sustained increase in

intensity throughout the remainder of the upper Ocala. This

pattern seems to be characteristic of the top of the Ocala in the

panhandle.

Figure 7 shows the section diagram and outcrop gamma ray

profile of the thickest exposure in the area of Miocene-age,

post-Suwannee carbonate, here called the Chattahoochee Formation.

This section is located on the east side of Jim Woodruff Dam

along the access road, the so-called type Chattahoochee. Here,

the gamma ray profile can be divided into two zones, a

stratigraphically upper, lower-intensity zone and a

stratigraphically lower zone characterized by many moderate

intensity peaks. This pattern is typical of the Miocene-age

carbonates in Florida. In general, the pattern of a

stratigraphically lower zone with higher intensity and a

stratigraphically higher zone with lower intensity can be seen in

















EAST JIM WOODRUFF


CP8 160 180


DAM


200 220 240 260

i --r r- jCf


4i'

I


Figure 7. Section diagram and outcrop gamma ray profile of
the thickest section exposed in the area of
post Suwannee carbonate.


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all the limestone formations in Florida, on both outcrop gamma

S ray profiles and borehole gamma ray logs." In addition, :the

overall gamma ray intensities found in the limestone sequence in

both the panhandle and the peninsula tend to decrease with age;

that is, the Miocene-age carbonate units show higher average

intensity than the Suwannee which, in turn, records as higher

than the Marianna, and the Marianna shows slightly higher average

intensities than the Ocala.

Figure 8 shows a composite of panhandle carbonate section

profiles which illustrates the appearance of a hypothetical

outcroo-profle for an outcrop in which all.-feur~formlatifione aer- -

present and developed to more or less typical extent for the

area. The absolute intensity scales of each of the profiles were

matched.and each profile was plotted in its correct stratigraphic

position. A general decreasing intensity with increasing depth

and age can be clearly seen.

Moving to the peninsula, Figure 9 shows an exposure along

the Cross-Florida Barge Canal at the 19 and 98 bridge in Citrus

County, in the west-central peninsula of Florida, near Inglis.

The Avon Park-Ocala contact is shown by the abrupt lithologic

change from brown and orange dolostone below to white Ocala

limestone above, with a thin organic peat seam separating the

formations. The gamma ray profile clearly shows the contact by a

moderate intensity peak at the peat seam. The pure limestone of

the Ocala above is recorded as a very low, even intensity, and

the Avon Park dolostone below as slightly higher sustained

intensity. This pattern is characteristic and is very common on


_



















CHATTAHOOCHEE


I I


8UWANNEE


MARIANNA


OCALA


INCREASING CPS **


Figure 8. Composite of panhandle carbonate-section outcrop
gamma ray profiles.








Figure 9.


Outcrop gamma ray profile and section diagram of the Avon Park-
Ocala contact in a section near Inglis.


BARGE CANAL AND U.S.19/98
CITRUS CO.


80 1


00 120




OCALA


140 160

~~1~h


F AVON PARK

S' 1 .., ... .


CPS,-.


I
22'


_








borehole gamma ray logs everywhere in the peninsula where both

formations occur together. For example, Figure 10 shows a

borehole gamma ray log from Lake County which illustrates a very

pronounced Avon Park-Ocala contact. Typically in the Lake County

area, the upper Avon Park is extremely rich in peat, organic

material and organic-rich clay. It has been postulated that this

material represents cavern-fill or is otherwise paleokarst-

related, having formed when the top of the Avon Park was

subaerially exposed before deposition of the Ocala sediments.

Figure 11 shows the lithologic section diagram and gamma ray

profile of the base of the Suwannee and top of the Ocala in

Hernando County, also in the west-central peninsula. This is the

Lansing Quarry, the lower portion, showing the Ocala-Suwannee

contact. The soft, calciruditic, Lepidocyclina-sp.-rich Ocala at

the base is recorded as a low, even-intensity trace. The

differentially-recrystallized, much-finer-grained Suwannee

immediately above the contact is recorded as a marked and

sustained increase in intensity, beginning at the contact.

Lithologically, the contact itself consists of a very thin,

orange, very soft, argillaceous, calcilutitic bed with very thin,

very hard, recrystallized beds above and below. The Suwannee

contains beds of recrystallized dolomitic limestone, whereas the

Ocala is generally much more homogeneous, soft, pure limestone.

In the upper portion of the section, the very hard,

recrystallized, molluskan-moldic limestone and dolomitic

limestone of the upper Suwannee is recorded as a low, even trace.





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LANSING QUARRY
HERNANDO COUNTY


CPS 60


80


100


Figure 11. Section diagram and outcrop gamma ray profile of the
lower portion of the Lansing Quarry, Hernando County.


I -L- I .L.








Figure 12 shows a borehole gamma ray log from western

Sarasota County which illustrates this same pattern in the

subsurface. The lower portion of the Suwannee is moderately high

intensity, whereas the upper portion is low, even intensity on

the gamma ray log. The higher-intensity, Miocene-age carbonates

lie above the Suwannee and the lower-intensity Ocala lies below.

The borehole gamma ray log illustrated in Figure 13 is from

a well located on the southern barrier island in Indian River

County along the east-central Atlantic coast where there exists

an anomolous thickness of Suwannee. Here can be seen a similar

gamma ray trace pattern with a lower, higher-intensity zone and-

an upper, lower-intensity zone. In this area, the Suwannee is

bounded above by the very-high-gamma-ray-intensity Hawthorn, and

below by the very-low-intensity Ocala.

The section in Figure 14 illustrates the uppermost limestone

section in the peninsula as exposed in Hernando County at the old

Camp Quarry northeast of Brooksville. Again, the upper Suwannee

at the base of the exposure shows low, even intensity on the

gamma ray profile. The argillaceous and arenaceous post-Suwannee

limestone and clay above the Suwannee record as moderate

intensity peaks with thin, lower intensity valleys between. This

unit is the lithologic equivalent of the panhandle Chattahoochee

Formation and exhibits an identical gamma ray trace pattern.

Although this paper has featured gamma ray profiles from the

carbonate section exclusively,-this same technique was applied to

many of the younger formations exposed in Florida. Figure 15

shows an example. Gamma ray profiles were constructed from most




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Figure 12. Borehcle gamma ray log from western Sarasota County.


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'


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lll ;'? -IrTTI + ", i+'-r;-+ 4"P ,-,' .. .









....-. HAWTHORN

I 1 :7 -..:.-.:-: :r: .' .- .
" ..... .... ..... --
-,- f


. ..


- .-- ... T -.- t- ..- '-- -: : -! --" - "
I -, -. ....... . .


"...i
-- -----4-- ---.--~


-- -'------C---
--7


.- l .... -7! -


....... LI


F7F7 V7 41


i.- i.-| I


--------------------------- I--.- ---i
I__ i


* I.


-- .-. 600'



*. I_


S. ..i
. :- ..-


.--t-t_-------I


--~.. .;.--
. ._ .. .. .


I.


--700'-r


K i


II


-f-7-7

7. -..----- r::
~ti~-~.-.~ -- I~


.. .. .

'77


7 : -77.
[ ....
2.. i: : ." : I ., I. .


1 ... ... "


-1 T.. ...
'--;. l ---..- .... .. .. --::
-i:.: ........... : ~::i-. : : .:_ : ... : :1 _: :


OCALA 1' ".."
r,, =- -7- I I -
I --. -- -- A._- _


SCPS-


.-I ...4..-- -- '800

T -- -


SFigure 13. Borehole gamma ray log from the southern barrier island in
Indian River County.


S-- L_-C hlSI.BlfBa


S---IUWANNEE : i
L I-.- ..I... .--.. *-
.:-::.::~~~ ~~~~ '.: ::: ,: : .: .


i


------ .......1 -- -- -- ~ "~


-~-- ---,: .--.. ~..-. .. ~.~.: .~ __


m o m -


1~ 1 I
I


--- ------


- i i I I i


4- i:


-- ------ -----


- -- ------;-


S -. i -,!- .... Z .. ....


; =,


- ---------


_e~ --


i


..-. I-~i-


-r- t ....


: r


F--_-:


i= E-A~-~-=f;~i


I


_---;_.


-- C---- "-'
-- '-


r


., _.__. ii I


:+. I. .


I









Figure 14.


Outcrop gamma ray profile and section diagram of the section exposed
in the lower portion of the old Camp Quarry, llernando County.

OLD CAMP QUARRY

HERNANDO CO.
80 100 120 140 160 CPS
.I .




- F ujPrL~uich. L..~ 1 p


fi ~Zu'


LEON CO.
100 120
.....


UNDIFFERENTIATED


HAWTHORN


.i. I. ...I.. I


. I J ..


Figure 15. Outcrop gamma ray profile and section diagram of Jackson Bluff'
illustrating the construction of profiles on younger formations.


Leon County,


140


CP:


I .. .. I








of the classic exposures in the state, such as Jackson Bluff,

Leon County, shown in Figure 15. It was found that many of these

formations could also be traced from outcrop gamma ray profiles

into the subsurface and from well to well. However, possibly due

to a greater variation in lithology, these younger formations do

not always appear as well-defined patterns on borehole gamma ray

logs.

In summary, this paper correlates outcrop gamma ray profiles

and borehole gamma ray logs of the Tertiary carbonate section in

panhandle Florida and in the peninsula. It can be seen that the

technique of constructing gamma ray profiles from outcrops is

indeed applicable and useful in Florida. Constructed with the

use of a very sensitive hand-held scintillometer, the profiles

can be used to correlate lithology and formational boundaries

from outcrops into the subsurface. Correlation between outcrops

is also possible, but is of limited importance in Florida due to

the typically very limited thicknesses and relative scarcity of

exposures in this area. However, once characteristic formational

gamma ray trace patterns are determined from gamma ray profiles,

correlations can also be made more confidently in the subsurface

between borehole gamma ray logs.









REFERENCES
Chamberlain, A. K., 1984, Surface gamma ray logs: a correlation
tool for frontier areas: American Association of Petroleum
Geologists Bulletin v. 68, n. 8, pp. 1040-1043.

Ettensohn, F. R., Fulton, L. P., and Kepferle, R. C., 1979, Use
of scintillometer and gamma ray logs for correlation and
stratigraphy in homogeneous black shales: Geological
Society of America Bulletin, Part II, v. 90, pp. 828-849.

Keys, W. S., and MacCary, L. M., 1971, Application of borehole
geophysics to water resources investigations: Techniques of
Water Resource Investigations of the United States Geological
Survey, Book 2, Chapter El, 126 p.