Element Distribution in Some 

Shelf and Eugeosynclinal 

Black Shales

By JAMES D. VINE

CONTRIBUTIONS TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1214-E

The content and association of minor 

elements in different black-shale environments

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington. D.C. 20402 - Price 20 cents
CONTENTS

. Page

Abstract_______________________________________________________ El

Introduction.--____________________________________________________ 1

Acknowledgments. ________________________________________________ 3

Analytical methods and limitations..____________________________... 3

Statistical treatment of data__________________________________ 4

Description of sample sets_______________________.__________________ 8

 Sources of error_________________________________________ 16

Distribution and association of major elements._________ ________ 17

Carbon________________________._ 17

Aluminum..___________________________________________________ 17

Iron.._____________________________________ 18

Magnesium_________________________________________ 18

Calcium.. _______________________________________________ 18

Sodium_____________________________________________^______ 19

Potassium ________________________ 19

Titanium_____--___.________________________________________ 19

Manganese. ________________________________________________ 20

Distribution and association of minor elements._______________________ 20

Silver______________________________________ 20

Boron_____________________________________ 21

Barium____________________________________________________ 21

Beryllium. _._________________________________ 21

Cobalt___-_______-_-_____-____-___-___-_-_-_-_-________-_-._- 22

Chromium__________________________________________________ 22

Copper__________________________________ 23

Gallium__________________________________ 23

Lanthanum__________________________________________________ 23

Molybdenum. ________________________________________________ 24

Nickel______._____________________________ 24

Lead_____________________________________________________ 25

Scandium__________________________________________________ 25

Strontium._________________________________________________ 25

Vanadium____________________________________________________ 26

Yttrium_______________________________ 26

Zinc_______________________________________ 26

Zirconium. ________________________________________________ 27

Summary and conclusions..________________________________________ 27

References cited___________________________________________________ 29

in
IV CONTENTS

ILLUSTRATION

Page 

FIGURE 1. Map^showing black-shale sample localities. ________ ___ E13

TABLES

Page

TABLE 1. Percentile distribution of 27 elements in four sets of samples of

black shale.________________________________________ E5

2. Correlation coefficients for element pairs in four sets of samples

of black shale...-__ -__ _ _ _.. 10
CONTRIBUTIONS TO GEOCHEMISTRY

ELEMENT DISTRIBUTION IN SOME SHELF AND 

EUGEOSYNCLINAL BLACK SHALES

By JAMES D. VINE

ABSTRACT

Emission spectrographic analyses of 220 samples of black shale from Pennsylvanian rocks of the shelf area in the Eastern Interior coal province and from 

Ordovician and Silurian rocks of the western North America eugeosyncline have 

been compared. 'Some samples of tooth the shelf group and the eugeosynclinal 

group have high contents of vanadium, chromium, zinc, silver, and moderately 

high contents of nickel and copper. High molybdenum and nickel contents are 

characteristic of the samples from the shelf; high 'barium content is characterisic 

of the samples from the eugeosyncline.

INTRODUCTION

The significant enrichment of many minor elements in organic sedimentary rocks, including black shale, was emphasized by Krauskopf 

(1955). Since that time, much new information has been reported in 

the literature. Some of the data are tabulated by Wedepohl (1964, 

p. 308-311) in his discussion of the origin of the Kupferschiefer. A 

review of these and other similar published geochemical data on black 

shale suggests that many of the analyses are of samples selected because they were unusual in one or more respects. Moreover, the 

analyses are rarely identified with specific geologic environments in a 

manner that is adequate for making geochemical interpretations of significant volumes of black shale. This report includes a summary of 

chemical data pertaining to the distribution of elements in 220 samples 

of black shale from 2 geologic environments. The significance of 

the data is briefly interpreted with respect to the two contrasting 

environments of deposition.

Most workers (for example, Krauskopf, 1955; Wedepohl, 1964; 

Davidson and Lakin, 1961, 1962) have been interested in black shale 

because of the unusual concentration of minor elements, especially

El
E2 CONTRIBUTIONS TO GEOCHEMISTRY

the metal concentrations of potential economic value. For this reason much of the literature tends to give a misleading impression of the 

quantity of black shale enriched in metals. Furthermore, the term 

"black shale" is somewhat misleading, for as it is defined by Swanson (1961, p. 69) and used here, it is not restricted to a single lithologic type of carbonaceous claystone, but includes many other darkcolored fine-grained rocks. Some, such as the Chattanooga Shale, 

are chiefly siltstone (Conant and Swanson, 1961, p. 43); but others, 

such as the graptolitic black shale in the Vinini Formation and equivalent units in Nevada, are siliceous mudstone (Ketner and Smith, 

1963). The Kupferschiefer in Germany and the oil shale in the 

Green River Formation of Utah, Colorado, and Wyoming are marlstone (Wedepohl, 1964, p. 320-324; Bradley, 1931, p. 7). Pennsylvanian black shale in western Indiana is intermediate in composition 

between claystone and coal (Zangerl and Kichardson, 1963, p. 105- 

106).

A classification for black shale could be constructed on a triangular 

diagram using siltstone for one corner, marlstone for another, and 

coal for the third. Alternatives possible are the substitution of claystone for siltstone, chert for marlstone, and sapropel for coal. More 

generally, the corners could be thought of as (1) fine-grained detrital 

minerals, (2) chemically or biogenically precipitated mineral matter, 

and (3) carbonaceous organic matter. As there are several possibilities for each corner within the general category, this allows a wide 

range of rock types to be included in the general name of black shale. 

By this definition, black shale includes all rock types of intermediate 

composition but not the pure end member. It may also be inferred 

that this wide range of rock types includes examples from many geologic environments, with possibilities for very different minor-element 

concentrations.

Such a classification finds further application in studying the distribution of minor elments in black shale. Thus, any specific element 

may occur principally in that fraction of a rock which is represented 

by an end member on the triangular diagram, or it may be included in 

two or more such fractions. For example, titanium may occur chiefly 

in the detrital-mineral fraction, but copper may be divided equally 

between the organic fraction and the chemically or biogenically precipitated fraction. Knowing which fraction of a rock contained 

the major share of each minor element facilitates determining whether 

each minor element was contained in the crystal lattice of a specific 

mineral or was held by chemical sorption. This, in turn, would lead 

to a better understanding of how certain elements become concentrated in some beds of black shale.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E3

ACKNOWLEDGMENTS

Many individuals contributed directly or indirectly to the collection 

and analysis of the samples and the processing of the data used in the 

preparation of this report. R. H. Calvert, T. M. Kehn, and J. W. 

Palmer aided in collecting the samples in sets 1 and 2; Dr. Rainer 

Zangerl, of the Chicago Natural History Museum, donated the samples 

in set 3; J. P. Albers, Michael Churkin, Jr., R. R. Coats, K. B. Ketner, 

R. J. Kleinhampl, R. J. Roberts, D. C. Ross, J. F. Smith, Jr., and R. G. 

Yates aided in collecting the samples comprising set 4.

Spectrographic analyses for part of set 4 were made in the U.S. 

Geological Survey laboratory in Menlo Park, Calif., by Chris Heropoulos. The remainder of the analyses from set 4 and the other three 

sets were made in the U.S. Geological Survey laboratory in Denver, 

Colo., by J. C. Hamilton and A. L. Sutton, Jr. Carbon analyses were 

made by I. C. Frost. The analytical data were transcribed to datacoding and retrieval cards by Mary S. Niles and Patricia Zimmerman. 

Ralph Eicher provided the data transformation, control cards, and 

programing advice for the machine computations.

ANALYTICAL METHODS AND LIMITATIONS

A 6-step method of emission Spectrographic analysis was used in 

both laboratories for all samples analyzed. This technique is similar 

to the 3-step method described by Myers, Havens, and Dunton (1961) 

except that in the 6-step method the operator compares the spectrogram of the sample with standard plates on which the amount of each 

element is increased by increments that are %-order of magnitude instead of %-order. The results are reported in percent to the nearest 

number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, and 0.1, which represent 

approximate midpoints of group data on a geometric scale. The assigned group for 6-step results will include the quantitative value 

about 30 percent of the time. The analyst normally looks for 51 elements. This report discusses only 26 elements that were reported consistently from the samples of black shale and have a range of values 

adequate to allow valid statistical treatment. Other elements, for example ytterbium and neodymium, were reported in some of the samples 

but not with sufficient regularity to treat statistically. Silicon was 

reported in all samples in major amounts or in near major amounts, 

but too many values were reported in the category: "greater than 10 

percent" for statistical treatment. The approximate lower limit of 

detection for the elements discussed is, in percent, as follows:
E4 CONTRIBUTIONS TO GEOCHEMISTRY

Approximate Approximate

lower limit lower limit

of detection of detection

Element (percent) Element (percent)

Al ___________________ 0. 001

Fe __________________ .0008

Mg __________________ . 0005

Ca _________________ .005

Na ________________ .05

K __________________ .7

Ti __________________ .0002

Mn _________________ . 0002

Ag ________________ .0001

B __________________ .002

Ba ________________ .0002

Be ________________ .0001

Co ________________ .0005

Cr _________________ 0.0001

Cu ________________ .0001

Ga _________________ .0002

La _________________ .002

Mo _________________ . 0005

Ni __________________ . 0003

Pb _________________ .001

Sc __________________ . 0005

Sr _________________ . 0002

V _________________ .001

Y _________________ .001

Zn ________________ .02

Zr __________________ . 001

The content of organic carbon was determined by making separate 

analyses for total carbon and carbonate carbon and taking the difference according to the method outlined in Tourtelot, Huffman, and 

Rader (1964, p. D74).

STATISTICAL TREATMENT OF DATA

Analyses of the 220 black shale samples were coded and incorporated 

in a geochemical data storage and retrieval system employing IBM 

punch cards. From these cards a machine print-out of the analyses 

suitable for direct reproduction was prepared; this print-out has been 

released as an open-file report (Vine, 1965). These cards were then 

used as input for converting the analyses to a new format on another 

set of cards suitable for machine computation of grouped data. Because the spectrographic analyses are reported by 1/6-order class 

intervals, the carbon analyses were grouped in the same class intervals. 

Numerous univariate and bivariate statistics were computed including 

arithmetic and goemetric means, numerical and percent frequency for 

each class interval, and coefficient of correlation between all pairs of 

variables. It was not possible to obtain a complete set of univariate 

and bivariate statistics because the original data included a number 

of rejected observations (elements for which the analyst reported one 

or more values as "less than," "greater-than," or "not detected"). The 

data presented in this report are grouped into the percentile categories 5, 25, 50, 75, and 95 the 50 percentile being equivalent to the 

median, and the 25 and Y5 percentiles being equivalent to the first and 

third quartiles, respectively. This grouping provides a suitable measure of central tendency, as well as of the range and nature of the data 

distribution. Table 1 lists these values together with the calculated 

values for arithmetic and geometric means for those elements having no 

rejected observations. Table 1 also lists the ratio, ~P95/P5 (the quotient 

of the 95 percentile divided by the 5 percentile), in order to provide a 

measure of the ranges for different elements.
TABLE 1. Percentile distribution of 27 elements in four sets of 

[Average abuadance: A, shale; 1 B, pelagic sediment;2 C, carboaaceous samples 

Element

Al... 

Fe.... ...

Mg._... ....

Ca.. ... .-

Na.... __ ..

K.. ....... ..

Ti.. -

Mn 

Set

1 

2 

3

4 

1 

2 

3 

4 

1 

2 

3

4 

1

2 

3 

4

1

2 

3

4

1 

2 

3

4 

1 

2 

3

4 

1 

2 

3

4

Values, in percent, for indicated percentile

Ps

7 

3 

1.5

1.5 

2 

1 

1.5 

.3 

.7 

.3 

.2

.2 

.05 

.02 

.1 

.05 

.7

.2 

.2

.05 

2 

1.5 

1.5

1 

.15 

.1 

.1

.05 

.005 

.0015 

.005

.001

P«

7 

7 

3

3

5 

1.5 

2 

.7 

.7 

.5 

.3

.5 

.2 

.05 

.2 

.1 

1

.5 

.2

.1 

3

2 

2

2 

.2 

.15 

.1

.1

.015 

.003 

.007

.002

PJO

>10 

7 

3

3 

5

2 

2 

1.5

.7 

.7 

.5

.7 

.3 

.1 

.3 

.3 

1

.7 

.3

.2 

3 

2 

2

3 

.2 

.15 

.1

.2

.015 

.005 

.007

.007

P?5

7 

7

7 

7 

2 

2 

2 

1 

.7 

.7

1.5 

.5 

.2 

.5 

3 

1

1 

1

.3 

3 

2 

3

5 

.2 

.2 

.15

.2 

.03 

.01 

.01

.015

PS5

>10 

7

>10 

7 

5 

3 

5 

1 

.7 

1

5 

3 

1 

1 

>10 

1

1

1.5

1 

5 

3 

5

5 

.2 

.2 

.3

.3 

.15 

.03 

.015

.05

Arithmetic 

mean

2.3 

1.7

.79 

.60 

.52

1.4 

.53 

.27 

.35

.95

.84 

.56

2.9

.27

.21 

.16 

.14

.19 

.034 

.0098 

.0084

.012

Geometric 

mean

2.2 

1.3

.77 

.56 

.48

.95 

.30 

.11 

.27

.93

.64 

.44

2.8

.24

.20 

.15 

.13

.15 

.021 

.0054 

.008

.0064

Ra

Po

>

>

N^

1

2

6

5

1

>20

2

3

2

5

See footnotes at end of table.
TABLE 1. Percentile distribution of #7 elements in four sets of sample

Element

Ag_... 

B.... ....

Ba..--.-.-..

Be..........

Co..........

Cr.. ........

Cu..........

Qa..........

La..........

Set

1

2 

3 

4 

1 

2 

3 

4 

1 

2 

3

4 

1 

2 

3 

4 

1 

2 

3 

4 

1 

2 

3 

4 

1 

2 

3 

4 

1 

2 

3

4 

1 

2 

3 

4

Values, In percent, for Indicated percentile

P»

<0.0002

.002 

<.002 

<.003 

<.003 

.03 

.02 

.015

.02 

.00015 

.00015

.001

.0007

.007 

.007 

.01 

.003 

.002 

.0015 

.01 

.0007 

.002 

.001 

.001

.0005 

.003 

<.002 

<.003

PJJ

<0.0001 

.0003

.002 

.002. 

.003 

.005 

.03 

.03 

.02

.07 

.00015 

.00015 

<. 00015

.001 

<.0002 

.0007

.007 

.01 

.02 

.007 

.003 

.005 

.015 

.003 

.002 

.0015 

.0015

.001 

.003 

.003 

.003 

<.003

PM

0.0001 

.0005

.003 

.003 

.003 

.007 

.05 

.03 

.02

.1

.0002 

.0002 

.0002 

<. 00015 

.001 

.0003 

.001 

<.0007 

.01 

.015 

.03 

.01 

.005 

.007 

.015 

.005 

.002 

.002 

.0015

.0015 

.005 

.003 

.005 

.003

P78

<0.0001 

.0002 

.0005 

<.0001 

.005 

.005 

.007 

.01 

.05 

.03 

.03

.2 

.0002 

.0002 

.0002 

.0002 

.0015 

.001 

.001 

.0007 

.015 

.02 

.03 

.015 

.007 

.01 

.015 

.01 

.002 

.002 

.002

.002 

.005 

.005 

.005 

.005

P»»

0.0002 

.0002 

.0007 

.0005 

.005 

.005 

.01 

.02 

.07 

.07 

.03

.5 

.0003 

.0002 

.0003 

.0003 

.002 

.001 

.0015 

.0015 

.015 

.03 

.05 

.03 

.007 

.01 

.02 

.02 

.003 

.002 

.003

.003 

.005 

.005 

.005 

.007

Arithmetic 

mean

0.043 

.037 

.023

.00022

.0012

.001

.011 

.017 

.032 

.012 

.0047 

.0064 

.015

.0022 

.0019 

.002

.0040

Geometric 

mean

0.041 

.033 

.022

.00021

.0012

.05097

.010 

.014 

.029 

.009 

.0044 

.0053 

.015

.0022 

.0018 

.0018

.0040

Rat

Pw/

>2 

>2 

>3

>5 

2

>2

>3

>6

2

3

2

25 

2 

1

>2 

>2 

2 

>5

2 

>2 

2 

4

5 

10 

3

6

2 

28

1

2 

3

6 

1

>2

>1.

>2
Mo.........

Ni.. ........

Ph.... ......

Sc..._. ...... 

T5r...__ ......

V.... _ ....

Y__ .........

Zn. .........

Zr...........

C.. .-- .__

1

2 

3 

4 

1 

2 

3 

4 

1 

2 

3 

4 

1 

2 

3 

4 

1 

2 

3

4 

1

2 

3 

4 

1 

2 

3 

4 

1

3 

4 

1 

2 

3

4 

1 

2 

3

4

<.0005 

.015

.002 

.002 

.01 

<.0005 

.0015 

.001 

<.001

.001 

.0007 

.0007 

<.0007 

.01 

.007 

.003

.003 

.007

.007 

.02 

.005 

.002 

.001 

.0015 

.001

.005 

.003 

.002

.003 

1.5 

2 

10

<.0005 

.0005 

.03

.003 

.005 

.02 

.0005 

.002 

.0015 

.002 

<.001 

. .0015 

.001 

.001 

.0007 

.015 

.01 

.007

.005 

.01

.007 

.07 

.01 

.002 

.002 

.002 

.0015

<.05

.07 

.005 

.003

.007 

3 

10 

15

.0015 

.005 

.03 

<.0005 

.007 

.007 

.03 

.0015 

.002 

.002 

.003 

.001 

.0015 

.0015 

.001 

.001 

.02 

.015 

.01

.01 

.015

.02 

.1 

.02 

.003 

.002 

.003 

002

.07

.007 

,005 

.003

.007 

5 

15 

30

.003 

.02 

.05 

.001 

.01 

.01 

.03 

.005 

.003 . 

.003 

.005 

.0015 

.002 

.0015 

.001 

.0015 

.02 

.02 

.01

.015 

.02

.05 

.15 

.05 

. .003 

.003 

.005 

.002 

<.03 

<.05 

.15 

<.03 

.01 

.007 

.005

.015 

10 

20 

50

.03 

.03 

.07 

.005 

.015 

.015 

.07 

.01 

.005 

.007 

.007 

.003 

.002 

.0015 

.0015 

.002 

.02 

.02 

.015

.05 

.05

.05 

.2 

.2 

.005 

.003 

.007 

.007 

.07 

.05 

.3 

.10 

.01 

.01 

.007

.02 

15 

30 

50

.040

.0071 

.0077 

.032

.0027

.0016

.0011

.021 

.015 

.0097

.013 

.018

.032 

.12 

.042 

.003

.004

.0075 

.0058 

.0039

7.3 

18 

34.8

.037

.0060 

.0060 

.028

.0025

' .0016

.0011

.019 

.014 

.0087

.0096 

.015

.022 

.10 

.023 

.0029

.0034

.0071 

.0052 

.0037

5.5 

11.8 

30.3

>60 

>60 

4.

>10 

7.

7.

7 

>20 

3.

7 

>7 

>3 

2 

2 

2 

>2.

1 

2.

5

16.

7.

7.

10 

40 

2.

3 

4.

7 

>2.

>1 

>6

^O 

2 

3.

3.

10 

15 

5

> Averape for shales, Turekian and Wedepohl (1961, table 2).

»Average of 22 samples of pelagic sediment cores from the eastern Pacific, Goldberg 

and Arrhenius (1958, table 9).

 ' Average of 14 samples of Pierre Shale containing more than 1 percent organic carbon; 

minor elements after Tourtelot, Schultz, and Oil! (I960,, table 205.1), major elements

after H. A. Tourtelot (wr

* Average of 47 coal-bed 

others (1964, table 7).

4 Distribution of sample 
E8 CONTRIBUTIONS TO GEOCHEMISTRY

Published values for the abundance of elements in some sediments 

and sedimentary rocks taken from four recent references are also listed 

in table 1. Included are the average values listed (1) by Turekian and 

Wedepohl (1961, table 2) for the abundance of elements in shales; (2) 

by Goldberg and Arrhenius (1958, table 9) for the abundance of elements in 22 samples of pelagic sediment cores from the eastern Pacific; 

(3) by Tourtelot, 'Schultz, and Gill (1960), table 205.1) for the abundance of elements in 14 samples of Pierre Shale that had more than 1 

percent organic carbon; and (4) by Zubovic, Stadnichenko, and 

Sheffey (1964, table 7) for the average content of minor elements in 

coal beds from the Eastern Interior coal region. These published values 

are average (arithmetic mean) values; therefore, it is not statistically 

valid to make direct comparisons with the median values of table 1. 

Where both median and arithmetic mean values were calculated for 

the samples of black shale in this study, the arithmetic-mean values are 

usually greater.

Whereas values for the median and other percentile categories in 

table 1 are listed according to the same series of 6 numbers used in 

reporting the 6-step spectrographic analyses, the arithmetic and geometric means are rounded to two digits. This is not intended to imply 

greater accuracy for the arithmetic and geometric means than for the 

percentile categories. The second digit is retained because it is a useful 

indication of the skewness of the sample distribution.

In order to test the strength of association between various elements, 

the product moment coefficient of correlation was calculated for every 

pair of elements from every set, if there were no rejected observations 

(see table 2). The 99- and 99.9-percent levels of significance shown on 

the table for each set are quoted from Davies (1954, p. 276) and are 

based only on the number of samples. As this method assumes a 

normal frequency distribution of the sample data, it may give a misleading impression of the strength of association for element pairs that 

do not approach the ideal distribution, as for example, those elements 

having a range of three or fewer class intervals.

DESCRIPTION OF SAMPLE SETS

The chemical data that are the basis for this report are derived from 

the analyses of 220 samples of black shale divided into four sets that 

are individually summarized. Descriptions of individual samples, 

localities, and 6-step spectrographic analyses of all samples are tabulated in a separate report that has been placed on open file by the U.S. 

Geological Survey (Vine, 1965). Only the summary statistics and 

interpretation of the analyses are presented here. Three sets represent 

black shale associated with coal beds of Pennsylvanian age in the Eastern Interior coal province; the fourth set is composed of samples of
E9

graptolitic shale from the western and transitional facies of Ordovician 

and Silurian rocks in the Frazer belt (of Kay, 1947).

Sets 1 and 2 consist of core and outcrop samples, respectively, of 

black shale in the Tradewater and Carbondale Formations of the western Kentucky coal field (fig. 1). Each set includes numerous core or 

channel samples of black shale from beds 1 foot thick or more that lie 

directly above coal beds in a cyclic stratigraphic sequence. Both sets 

also include a few samples of black shale from below coal beds or between closely spaced coal beds. Although most of the beds of black 

shale are less than 3 feet thick, a few are thicker. Many contain 

brachiopods, conodonts, fish scales; and fins, and other faunal remains 

similar to the black shales described by Zangerl and Richardson (1963).

The core samples comprising set 1 were taken from a group of four 

borings, drilled in connection with the Kentucky geologic mapping 

project at locations selected to provide the maximum stratigraphic and 

structural information in an area of poor outcrops and to aid in determining the thickness, grade, and reserves of coal. The complete sequence of black shales penetrated by these four borings is included in 

set 1. The set is probably representative of about 5 beds of unweathered black shale aggregating about 13 feet in thickness, at depths of 

less than 200 feet in the vicinity of Owensboro, Ky. 'Similar black 

shale probably underlies several quadrangles in the northern part of 

the Western Kentucky coal field.

The samples comprising set 2 were collected from all the readily 

accessible natural and artificial exposures of black shale in the areas 

near Owensboro and Madisonville, Ky., that were known to the U.S. 

Geological 'Survey field geologists mapping these areas in the spring of 

3964. Set 2 is probably representative of about 10 beds of slightly 

weathered black shale that have an aggregate thickness of about 18 feet 

as they occur at or near the outcrop in the Western Kentucky coal field. 

'Similar rock probably underlies much of the coal field.

Set 3 consists of a complete sequence of thin laminae split from a 12- 

inch bed of metal-rich black shale that lies above coal III-A in the 

Linton Formation of Parke County, Ind. (fig. 1). This bed was named 

the Mecca Quarry Shale Member by Zangerl and Richardson (1963); 

it was studied in great detail by them because it contains a remarkably 

well preserved fauna of Pennsylvanian sharks and other fish in association with invertebrate remains. Included in the report (Zangerl 

and Richardson, 1963, p. 99) are several spectrographic analyses of the 

shale that indicate unusually large amounts of vanadium, zinc, and 

several other metals. These first analyses were intended to aid in 

understanding the environment of deposition of the contained fossils, 

and it was probably not anticipated that they would be rich in metals.
E10 CONTRIBUTIONS TO GEOCHEMISTRY

o 

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E14 CONTRIBUTIONS TO GEOCHEMISTRY

The association of abundant well-preserved fossils with a metal-rich 

shale, however, may be evidence of a toxic environment. The Indiana 

III-A coal bed and the overlying black shale are recognized over much 

of the Eastern Interior coal province. Stratigraphic equivalents of 

the Mecca Quarry Shale Member in the Western Kentucky coal field 

are included among the samples of sets 1 and 2. * Although the coal 

and black shale are widespread, the chemical composition of the black 

shale samples in set 3 may not represent more than a few hundred 

acres in the vicinity of the Mecca Quarry, Parke County, Ind.

Set 4 includes outcrop samples from widely scattered localities in 

California, Nevada, Idaho, Washington, and British Columbia collected from the graptolitic shale facies that was deposited in or marginal to the lower Paleozoic eugeosyncline of western North America. 

Several samples included in this set were collected from localities 

previously reported to be metal rich. One sample is from the locality 

described by Davidson and Lakin (1961) as the Comus Formation, 

Edna Mountains, Nev., and two were collected from the locality 

described by Davidson and Lakin (1962) as "Taylor Canyon, Elko 

County, Nevada." Other samples were collected wherever shale 

exposures of the Ordovician and Silurian "western" or "transitional" 

f acies as defined by Roberts and others (1958) could be found. Roberts, Hotz, Gilluly, and Ferguson (1958, p. 2816) estimated that shale 

makes up 20-40 percent of the eugeosynclinal stratigraphic sequence 

in central Nevada. Many of the specific localities examined and sampled were suggested to me by colleagues in the U.S. Geological Survey 

or were located from published descriptions of black or graptolitic 

shale. They include several localities from which graptolitic fossils 

were collected by Ross and Berry (1963). Rocks of the graptolitic 

f acies were deposited to the west of, and contrast markedly with, the 

miogeosynclinal rocks typical of eastern Nevada and Utah, which are 

largely carbonate rocks. The eugeosynclinal strata are characteristically siliceous (Ketner and Smith, 1963) and dark in color because of 

large amounts of included carbonaceous matter. Although there has 

been much speculation regarding the origin and environment of deposition including the depth of water in which the graptolitic shales were 

deposited, there is as yet no general agreement (Ross, 1961). However, many field geologists, including R. J. Roberts (oral commun., 

1962), believe that the eugeosynclinal deposits accumulated in deep 

water, far from the continental shore. Ruedemann (1934) regarded 

most of the graptolites and such associated forms as the crustacean 

Caryocaris as being of planktonic origin. These rocks are therefore 

similar in many respects to the carbonaceous and siliceous rocks of the 

Monterey Formation of Miocene age in California that Bramlette
E15

(1946, p. 50-51) thought were derived in large part from such planktonic organisms as diatoms and algae.

The samples making up set 4 are intended to be representative of the 

graptolitic shale facies of western North America. These rocks crop 

out in a region of complex structure, and the details of stratigraphic 

succession have not been worked out. Therefore, it is difficult to estimate the volume of black shale that is represented. Clearly, however, 

the 75 samples of set 4 represent a far greater volume of rock than 

do the 145 samples in the first 3 sets.

The environments of deposition, for those samples collected from 

the shelf area and those samples collected from the eugeosynclinal area 

are in striking contrast. Whereas the samples of black shale in sets 

1-3 may be regarded as characteristic of a near-shore shallow-water 

environment on the continental shelf, the samples of black shale in set 

4 are probably characteristic of a deep marine environment remote 

from the influence of the continent. Furthermore, the composition of 

the organic matter preserved in the two environments is probably quite 

different. As pointed out by Vinogradov (1953, p. 134^135), preDevonian black shales did not include the humic decomposition products of lignin derived from the higher land plants, which had not 

evolved significantly until Devonian time. The organic matter preserved in the samples of sets 1-3 presumably includes abundant humic 

matter similar to the "liver mud" described by Spackman, Scholl, and 

Taft (1964, p. 28-29) derived from vascular land plants growing in 

the nearby coal swamps; in contrast, the organic matter preserved in 

the samples of set 4 is presumably sapropelic.

Each set of samples differs from the others in some significant 

respect that justifies separate statistical treatment. The samples comprising set 1 are less weathered than the other two sets from the Eastern Interior coal province. The samples comprising sets 1 and 2 are 

relatively large channel and core samples from several different beds, 

whereas the samples comprising set 3 are individual thin laminae from 

a single bed. Set 3 therefore represents a smaller scale of sampling. 

The samples comprising set 4 differ from the first three sets not only 

because they are from older rocks in a different environment of deposition, but because they had a wide geographic distribution. They 

represent a larger scale of sampling than the other sample sets. 

Therefore, whatever interpretation is given to the geochemical significance of the analytical data must consider these differences. Some of 

the more pertinent differences are outlined in the table below.
E16 CONTRIBUTIONS TO GEOCHEMISTRY

*DO

I

2 

3

4

Number ofsamples

66 

42 

37

75

Number oflocalities

4 

20 

1

61

Area or 

region

Western 

Kentucky.

... -do.. ......

Western 

North 

America.

Sample

description 

(generalized)

0.5 ft coaly 

shale, drill 

core. 

0.75 ft coaly 

shale, outcrop.

shale, quarry; 

1.0 ft siliceous 

shale, outcrop.

Degree of 

weathering

Unweathered.

Slightly 

weathered.

.....do. . 

.....do........

Age

Pennsylvanian.

.....do.. ...... 

.....do........

Ordoviclan 

and 

Silurian.

Depositional 

environment

Transgressive 

brackish or 

marine, shelf. 

Do.

Do.

Eugeosyncline 

(abyssal 

slope).

SOURCES OF ERROR

No geochemical interpretation, especially one involving statistical 

treatment of data, should be attempted without recognizing the many 

possible sources for error. First, the plan of sample collection, if not 

random, may introduce a bias that is difficult to evaluate. Such a 

plan requires a geologic interpretation of the uniformity, areal distribution, and correlation of stratigraphic units that the samples are 

intended to represent. Because unweathered natural outcrops of 

black shale are rare, samples for this study had to be collected from 

a variety of artificial exposures and previously cored or quarried rock. 

The bias introduced into this study through failure to use truly random methods of sampling is probably no more significant than the 

errors common to most geologic investigations that attempt to represent any significant body of rock by a few chemical analyses of samples collected at natural outcrops, roadcuts, and similar exposures. 

Second, the precision and accuracy of the 6-step spectrographic method of analysis employed in this study is less than other more costly 

techniques. However, in trying to estimate a reasonable value for 

the abundance of a minor element in a given type of rock, as well as 

a range of values that might commonly be found, analysis of numerous 

samples by the 6-step spectrographic method is more informative than 

analysis of a few samples by a more precise method.

Perhaps the greatest danger with any geochemical interpretation is 

attributing to it greater significance than is warranted. This is especially true when one makes comparisons with data derived from samples collected for a different reason, analyzed by different techniques, 

and presented statistically using different measures of central tendency and dispersion. For this reason, comparisons with previously 

published data are not emphasized in this report. The new data are 

considered internally consistent enough to make valid comparisons 

between sample sets.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES El7

The distribution and association of individual elements can be 

determined from table 1, which shows for each set the percentile distribution of organic carbon and each of the 26 elements detected spectrographically, and table 2, which shows for each set the coefficient of 

correlation for element pairs. Two kinds of comparisons should be 

distinguished: (1) statements about strong positive or negative correlations between elements referring to coefficients of correlation having 

at least a 99-percent level of significance between element pairs in a 

specified sample set as shown in table 2 and (2) statements about 

direct or inverse variations between two elements in a series of sample 

sets, referring to the median content of one element that shows a setby-set change which varies directly or inversely with the median content of another element as shown in table 1.

CARBON

Sufficient organic carbon to impart a dark-gray to black color to 

the rock is characteristic of all the samples studied. Analyses for 

organic carbon were made for all samples comprising sets 1-3 and 

for a few samples of set 4. The median organic carbon analyses for 

set 1 is 5 percent; for set 2, 15 percent; and for set 3, 30 percent. 

The median organic carbon analysis for set 4 is estimated to be about 

2-3 percent. Of all the elements studied, organic carbon shows the 

greatest tendency to correlate negatively with most of the other elements, especially the other major elements. This tendency probably 

arises because no major element can vary independently of the others; 

the total element content must always approach 100 percent. Among 

the minor elements, copper and nickel show that most consistent 

positive correlation with organic carbon, and molybdenum shows the 

strongest positive correlation with carbon in a single set.

ALUMINUM

The median content of aluminum is greater than 10 percent for the 

samples in set 1,7 percent in set 2, and 3 percent in set 3. The change 

in these three sets varies inversely with the median content of organic 

carbon. The median content of aluminum for the samples in set 4 

is 3 percent, the same as set 3, which has the highest median carbon 

content. In set 4, however, the other major diluting element is presumed to be silicon, rather than carbon, as many of these samples 

are siliceous. The content of aluminum in all the samples of black 

shale is probably directly related to their clay mineral content. Consequently, of all elements studied except silicon, aluminum is the most
E18 CONTRIBUTIONS TO GEOCHEMISTRY

characteristic element of the detrital mineral fraction. Other elements having a strong correlation with aluminum probably are more 

abundant in the detrital-mineral fraction than in the organic matter 

or in the biogenically and chemically precipitated fraction. Coefficients of correlation for aluminum were calculated only for set 3, 

where aluminum has a strong positive correlation with gallium, magnesium, potassium, strontium, sodium, barium, manganese, titanium, 

and zirconium and a strong negative correlation with organic carbon.

IRON

The median content of iron ranges from 1.5 percent in samples of 

set 4 to 5 percent in those of set 1 which have been weathered the least. 

Iron occurs in pyrite or its secondary alteration products in most of 

these samples, but it has no strong positive correlation with other elements, such as copper, zinc, molybdenum, nickel, or cobalt that might 

also be expected to occur in sulfide minerals. In set 3, iron has a 

strong positive correlation with manganese and titanium, both of 

which form common oxides with iron. A strong positive correlation 

of iron with magnesium in the samples of set 4 may indicate the presence of the mineral ankerite.

MAGNESIUM

The content of magnesium in samples of set 4 ranges from 0.2 percent at the 5-percentile level to 5 percent at the 95-percentile level; 

yet the median content of samples in all 4 sets is very close 0.7 percent in sets 1, 2, and 4, and 0.5 percent in set 3. Magnesium has a 

strong positive correlation with many elements; with sodium, gallium, titanium, manganese, and strontium, it shows such correlation 

in more than one set. Except for titanium, most elements with which 

magnesium correlates could occur in more than one fraction of black 

shale, but they appear repeatedly in combinations that are most readily interpreted as detrital.

CALCIUM

Although the content of calcium has the widest range of all the 

major elements, sets 1, 3, and 4 have the same median content of 0.3 

percent, and set 2 has a median content of 0.1 percent. These median 

contents are significantly less than those for magnesium, which seems 

a little unusual. They are also significantly less than the average 

abundances in shale, pelagic sediment, and Pierre Shale (table 1, col. 

13). The environment of deposition for most of the samples of black 

shale was probably too acid for calcium carbonate to be stable, and 

therefore calcium remained in solution. Calcium has a strong positive 

correlation with only a few elements: nickel and copper in set 1 and
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E19

manganese in set 2; it also has a negative correlation with zirconium 

in set 1. This grouping of elements does not suggest any pattern of 

distribution that can be readily interpreted, except that calcium is 

nondetrital.

SODIUM

The median content of sodium ranges from 0.2 percent for the 

samples in set 4 to 1 percent for the samples in set 1. The occurrence 

of the highest median sodium content in the core samples from set 1 is 

in agreement with the findings of Gluskoter and Kees (1964) and Gluskoter (1965) in the Eastern Interior coal province that the chloride 

content of coal and the sodium chloride content of ground water associated with coal increases with depth. From this relation it may be 

inferred that part of the sodium in the core samples is derived from 

included pore moisture, or is lightly held in the mineral fraction by 

sorption or ion exchange. Probably a greater proportion of the sodium contained in samples from sets 2-4 is an essential part of specific 

minerals. Sodium has a strong positive correlation in sets 1-3 with 

magnesium and titanium, and in sets 2 and 3 with gallium, an element 

grouping suggestive of the detrital mineral fraction.

POTASSIUM

Potassium is consistently more abundant than sodium in the samples. The median content of potassium ranges only from 2 to 3 percent 

and the total range (ratio of P95/P5 ) is less than for sodium for 3 of 

the 4 sets. A strong positive correlation of potassium with the elements 

gallium, magnesium, and titanium as well as with sodium in set 3 indicates that potassium and sodium, are geochemically similar. The 

highest median potassium content occurs in samples of set 1, like that 

of sodium, indicating that potassium too may be subject to weathering 

at the outcrop.

TITANIUM

The median content of titanium ranges from 0.1 percent for the 

samples in set 3 to 0.2 percent for the samples in sets 1 and 4. The corresponding arithmetic means calculated to two digits range from 0.14 

to 0.21 percent titanium, means which appear to be significantly less 

than the average of 0.46 percent titanium in shale listed by Turekian 

and Wedepohl (1961, table 2). This divergence may be due to a greater proportion of detrital minerals in the shale samples used in 

compiling the data for average shale, as contrasted with a greater proportion of chemically or biogenically precipitated mineral matter and 

organic matter in the samples of black shale included in the present 

study. The median titanium content varies directly with the median
E20 CONTRIBUTIONS TO GEOCHEMISTRY

aluminum content in the first three sample sets, but in set 4 the median 

titanium is relatively high and the median aluminum is low. This 

variation may be due to an origin for the detrital fraction of set 4 from 

mafic volcanic rocks rich in titanium. Goldberg and Arrhenius (1958, 

p. 189) suggested a similar explanation for the relatively high content 

of titanium in pelagic sediment. Perhaps the high titanium content 

relative to the aluminum content of the samples in set 4 is due to a 

contribution from biogenically precipitated titanium, as suggested by 

Cressman (1962, p. T13) for the relatively high titanium content of 

some other siliceous sedimentary rocks.

MANGANESE

The content of manganese in the 4 sample sets has a very wide range, 

from 0.001 percent at the 5-percentile level of set 4 to 0.15 percent at 

the 95-percentile level of set 1. The arithmetic-mean content of manganese calculated to two digits ranges from 0.0084 percent in samples 

of set 3 to 0.034 percent in samples of set 1, which is significantly less 

than the 0.085 percent manganese listed for the average shale by 

Turekian and Wedepohl (1961, table 2). The higher content of manganese in the core samples of set 1, like the correspondingly higher 

content of sodium, may be due to the greater degree of weathering that 

has removed the more soluble part of the original manganese from the 

samples of the other three sets. The manganese remaining in the 

more weathered samples may be that which is tightly held in resistant 

minerals, for in set 3 manganese has a strong positive correlation with 

several elements including magnesium, gallium, sodium, potassium, 

titanium, iron, aluminum, and zirconium, elements which presumably 

occur in the detrital fraction of the black shale.

DISTRIBUTION AND ASSOCIATION OF MINOR 

ELEMENTS

SILVER

The silver content of most of the samples of black shale is less than 

the 0.0001 percent lower limit of detection of the 6-step spectrographic 

method. The median value of 0.0005 percent in the samples of set 3 

exceeds the 95 percentile of the samples in sets 1 and 2, but it is equal 

to the 95 percentile of samples in set 4. Thus, samples from the eugeosynclinal environment have local concentrations of silver as high as a 

single bed of metal-rich shale from the shelf environment. Although 

no coefficients of correlation were calculated between silver and other 

elements, because of insufficient data, inspection of the analyses suggests a probable positive correlation between high silver and high 

molybdenum, nickel, vanadium, and carbon.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E21 

BORON

In spite of the large variation in the proportions of detrital minerals 

and carbonaceous matter, the median boron content of the samples 

from the shelf environment, sets 1-3, is 0.003 percent. The 0.007 percent median boron content of set 4 indicates a significantly greater concentration of boron in the samples from the eugeosynclinal environment. Because several recent investigators (for example, Degens, 

Williams, and Keith, 1958) have considered the probability of boron 

being a salinity indicator, one might suspect that the greater content of 

boron in the samples in set 4 indicates a higher salinity environment 

for the eugeosynclinal samples. However, only the 0.02 percent boron 

at the 95-percentile level of samples in set 4 compares with the 0.03 

percent reported by Goldberg and Arrhenius (1958) for boron in 

pelagic sediments. Furthermore, Zubovic, Stadnichenko, and Sheffey 

(1964, table 7) reported about three times as much boron in coal (0.0096 

percent) as was found in black shale from the shelf environment. 

From this it would appear that a comparison of boron content in different rock types or environments cannot be used directly as a salinity 

indicator.

BARIUM

The contrast between set 4 and the other sets is even more marked 

for barium than for boron; the median content of 0.1 percent barium 

in the samples of set 4 exceeds even the 95-percentile value for the other 

samples. The samples from the eugeosynclinal environment are enriched in barium when compared with the samples from the shelf 

environment. Furthermore, barium shows a strong positive correlation with strontium, gallium, aluminum, magnesium, potassium, sodium, titanium, manganese, and scandium in set 3, such correlation suggesting that in this shelf environment what little barium is present 

occurs chiefly in the detrital-mineral fraction. Although coefficients 

of correlation were not calculated between barium and other elements 

for set 4, inspection of the analyses indicates a probable positive correlation between high barium and high vanadium but little or no correlation between barium and strontium. Inasmuch as the samples 

in set 4 include a relatively large proportion of chemically or biogenically precipitated mineral matter, it seems likely that some of the 

barium in these samples occurs as a discrete barium mineral precipitate, probably barite, as suggested by Goldberg and Arrhenius (1958, 

p. 188) for the occurrence of barium in Pacific pelagic sediments.

BERYLLIUM

The median content of beryllium is less than 0.00015 percent in the 

samples of set 4 and 0.0002 percent in the samples of sets 1-3, making
E22 CONTRIBUTIONS TO GEOCHEMISTRY

beryllium one of the least abundant elements of the ones that are 

commonly reported in these samples of black shale. Furthermore, 

only 0.0002-0.0003 percent beryllium was found even at the 95-percentile level in these samples. In contrast to the above generalizations, 

Stadnichenko, Zubovic, and Sheffey (1961) found the beryllium content of coal to be highly variable, some beds containing as much as 

0.0031 percent beryllium. Furthermore, they concluded (1961, p. 

279-281) that most of the beryllium is associated with the organic 

matter of the coal and not with the extraneous ash. In the samples of 

set 1, even though beryllium has a negative correlation with carbon, 

it has a strong positive correlation with vanadium, chromium, nickel, 

copper, and lanthanum. As a group, these five elements are probably 

concentrated in, or associated with, the organic-matter fraction of 

black shale.

COBALT

The total range in content of cobalt in the samples of black shale 

is not large, but the 0.001 percent median cobalt content of samples in 

set 1 is about three times the median content of 0.0003 percent in samples of set 2. So much difference between two similar sets of samples 

seems unusual, unless as was suggested for the difference in content 

of sodium and manganese between sets 1 and 2, it is a reflection of 

the sample depth and degree of leaching or weathering near the surface. The only significant correlation data for cobalt are for the 

samples in set 3. There, cobalt has a strong positive correlation with 

nickel and molybdenum, as well as a positive correlation with vanadium, copper, yttrium, and probably chromium. As a group, these 

elements are probably associated with, or concentrated in, the organicmatter fraction of the black shale samples.

CHROMIUM

The arithmetic-mean content of chromium, calculated to two digits, 

ranges from 0.011 percent for the samples in set 1 to 0.032 percent 

for the samples in set 3. These amounts appear to be only slightly 

greater than the average content of shale, which, according to Turekian 

and Wedepohl (1961, table 2), is 0.009 percent. Chromium has a 

strong positive correlation with vanadium in all four sample sets and 

with copper, nickel, and scandium in two sets each. These elements, 

as a group, are not assignable to a specific fraction of black shale, but 

it is considered significant that vanadium, copper, and nickel, at least, 

are probably associated with the organic-matter fraction.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E23 

COPPER

The median content of copper in the samples of black shale ranges 

from 0.005 percent in sets 1 and 4 to 0.015 percent in set 3. Except 

for set 3, the arithmetic-mean copper content is very close to the 0.0045 

percent listed by Turekian and Wedepohl (1961, table 2) for average 

shale. Even the 0.02 percent copper at the 95-percentile level of 

samples in sets 3 and 4 does not come close to the 0.074 percent listed 

by Goldberg and Arrhenius (1958, table 9) as the average copper 

content of 22 pelagic sediment cores from the Pacific. Moreover, copper is concentrated in economically significant amounts in other black 

shale units, such as the Kupferschiefer of Germany; so it is worth 

noting here that copper is one of the few elements that tends to correlate positively with carbon. Furthermore, copper has a strong positive correlation with vanadium, chromium, and nickel in sets 1 and 

2 and a moderately strong positive correlation with these same elements 

plus molybdenum in set 3. As a group, these elements are probably 

among the most closely associated with the organic-matter fraction 

of black shale.

GALLIUM

The total range in content of gallium in the 4 sets of samples of 

black shale is from 0.0005 percent at the 5-percentile level of samples 

in set 4 to 0.003 percent at the 95-percentile level of samples in sets 1,3, 

and 4. For all sets the median and arithmetic-mean contents of gallium are very close to the 0.0019 percent averages listed by Turekian 

and Wedepohl (1961, table 2) for shale and by Goldberg and Arrhenius (1958, table 9) for pelagic sediments. Gallium has an unusually 

strong positive correlation with aluminum, sodium, titanium, magnesium, potassium, and zirconium and a strong negative correlation 

with carbon in set 3. Goldschmidt (1954, p. 319) has emphasized 

gallium's close geochemical relation with aluminum, for which it 

readily substitutes, especially in clay minerals. Thus it is not surprising that gallium shows a strong positive correlation with those 

elements expected in clay minerals, as well as with other elements, 

such as titanium and zirconium, which occur in other minerals of the 

detrital-mineral fraction of black shale. When analyses for silicon 

and aluminum are not available, gallium is probably one of the most 

characteristic elements of the detrital-mineral fraction.

LANTHANUM

The median content of lanthanum is either 0.003 or 0.005 percent in 

all sample sets, and the highest content at the 95-percentile level is only 

O.OOY percent in set 4. These amounts are less than the average content of lanthanum in shale or pelagic sediment, but they are nearly one
E24 CONTRIBUTIONS TO GEOCHEMISTRY

order of magnitude greater than the 0.00051-percent average content 

that Zubovic, Stadnichenko, and Sheffey (1964, table 7) found in coal 

beds of the Eastern Interior region. Together, these observations 

suggest that lanthanum is more closely associated with the detritalmineral fraction than with either the organic fraction or the chemically or biogenically precipitated fraction of the black shale.

MOLYBDENUM

The molybdenum content is among the most variable of all the 

elements detected in the samples of black shale. The median content 

ranges from 0.0005 percent in samples of set 4 to 0.03 percent in samples of set 3. The samples of set 3 contain more molybdenum at the 

5-percentile level than do the samples of set 4 at the 95-percentile level. 

Even more significant, perhaps, is the fact that the median contents of 

molybdenum in the samples of sets 1 and 2, which are more nearly typical of shelf environment, are 3-10 times greater than the median content of molybdenum in samples of set 4 from the eugeosynclinal environment. Correlation data were calculated for molybdenum only for 

the samples in set 3, where it has a strong positive correlation with 

nickel, cobalt and carbon. Furthermore, if the median content of 

molybdenum and the median content of carbon are compared in sets 

1-3, a direct variation between molybdenum and carbon is evident. 

Coal from the Eastern Interior coal region (Zubovic and others, 1964, 

table 7) contained an average of only 0.00043 percent molybdenum, yet 

the molybdenum-rich samples in set 3 range from shale to coal in carbon content. The difference in molybdenum content between coal and 

black shale is probably due to the differing availability of molybdenum in a fresh-water coal swamp and in brackish or marine water 

adjacent to the strand line.

NICKEL

The total range in content of nickel from less than 0.0005 percent at 

the 5-percentile level of samples in set 4 to 0.07 percent at the 95-percentile level of samples in set 3 is the same as for molybdenum; but the 

range in content of individual sample sets is less than for molybdenum. 

The 0.0015-percent median content of nickel in set 4 is about one-twentieth that of set 3 and one-fifth that of sets 1 and 2, providing another 

example where samples from the shelf environment are much richer 

than samples from the eugeosynclinal environment. Correlation data 

were calculated for the samples in sets 1-3. Nickel has a moderate to 

strong positive correlation with vanadium, copper, and chromium in 

all three sets and also it tends to show a positive correlation with 

carbon. It is not concentrated in fresh water, however, for Zubovic, 

Stadnichenko, and Sheffey (1964, table 7) found an average of only 

0.0015 percent nickel in the coal beds of the Eastern Interior region.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E25 

LEAD

According to data compiled by Wedepohl (1964, p. 308-311), lead 

is less commonly enriched in black shale than vanadium, chromium, 

nickel, and molybdenum; yet there is a marked enrichment of lead in 

the Kupferschief er (Wedepohl, 1964, p. 332-334). The median lead 

content of sample sets 1-4 ranges from 0.001 to 0.003 percent. This 

is close to the amount in average shale and in the Pierre Shale (Tourtelot and others, 1960, table 205.1). Although the median content of 

lead in set 3 is higher than for the other sets, it may be significant 

that the 0.007-percent lead at the 95-percentile level is the same for 

samples in sets 2 and 3, suggesting that none of these samples contain 

unusual amounts of lead. Correlation data for lead are available 

only for set 1, wherein lead has a strong positive correlation with 

potassium and a moderately strong positive correlation with sodium 

and scandium. As a group, these elements suggest that at low concentrations lead is associated with the detrital-mineral fraction of the 

black shale.

SCANDIUM

Although scandium was detected in most of the samples of black 

shale, it has a limited range in content from less than 0.0007 percent 

at the 5-percentile level of set 4 to 0.002 percent at the 95-percentile 

level of sets 1 and 2. The median contents of scandium indicate no 

enrichment of this element with respect to average shale and a somewhat lower content than in pelagic sediment and the Pierre Shale 

(table 1). Correlation data calculated for sets 1 and 3 show that 

scandium has a moderate to strong positive correlation with sodium, 

vanadium, titanium, chromium, potassium, magnesium, and gallium 

in both sets and with zirconium, aluminum, barium, beryllium, lanthanum, and manganese in at least one set. As a group, these elements 

are not diagnostic of a single fraction, but they include several elements 

of the detrital-mineral fraction, as well as a few that are at least 

indirectly associated with the organic-matter fraction.

STRONTIUM

The median content of strontium ranges from 0.01 percent in samples of sets 3 and 4 to 0.02 percent in samples of set 1. For the samples in sets 2 and 3 where the correlation data are most complete, 

strontium has a moderate to strong correlation with magnesium, barium, titanium, sodium, gallium, and zirconium. In set 3 alone, it has a 

positive correlation with aluminum, iron, and potassium and a negative 

correlation with carbon. . If this were the only information, it would 

indicate that in.the shelf environment, strontium, like barium, is 

primarily associated with the detrital-mineral fraction of the black
E26 CONTRIBUTIONS TO GEOCHEMISTRY

shale. However, in set 1, strontium has a moderate positive correlation with copper, calcium, 'beryllium, chromium, and lanthanum, 

indicating that in the unweathered core samples some strontium may 

be associated with nondetrital minerals.

VANADIUM

Of all the metals reportedly enriched in black shales, vanadium is 

probably the most common, yet many black shales contain no more 

than the average 0.013 percent vanadium that Turekian and Wedepohl 

(1961, table 2) listed for shale. Thus, the median content of 0.015 to 

0.02 percent vanadium of the samples in sets 1, 2, and 4 is scarcely 

more than in average shale. The 0.1-percent median vanadium content of samples in set 3 is fairly typical of metal-rich black shale. 

At the 95-percentile level the samples from sets 3 and 4 both contain 

0.2 percent vanadium; the highest 5 percent of the samples from the 

eugeosynclinal environment contain, then, as much vanadium as the 

highest 5 percent of a metal-rich bed in the shelf environment. 

Vanadium has a strong positive correlation with chromium in 'all sets, 

with nickel in the first three, with copper in the first two, and with 

scandium in the first and third. Vanadium and molybdenum have a 

moderately strong positive correlation in set 3, the only set for which 

the data were calculated. In sets 1, 2, and 3, the median content of 

vanadium has a direct variation with the median content of carbon, 

yet there is no strong correlation between vanadium and carbon. Thus, 

vanadium probably has an indirect association with the organic-matter 

fraction of the samples of black shale.

YTTRIUM

The yttrium content of the samples of black shale ranges from 0.001 

percent at the 5-percentile level of sets 2 and 4 to 0.007 percent at the 

95-percentile level of sets 3 and 4. Although not enriched in the black 

shale, yttrium, nevertheless, tends to have a positive correlation in 

set 3 with elements such as nickel and molybdenum, both of which are 

enriched in, and probably associated with, the organic-matter fraction 

of the rock. Yttrium has an insignificant or negative correlation 

with aluminum, gallium, titanium, zirconium, and other elements that 

occur chiefly in the detrital-mineral fraction of black shale; therefore 

it is probably chiefly associated with the nondetrital faction.

ZINC

The lower limit of zinc detection by the 6-step spectrographic 

method is about 0.02 percent, which was too high to disclose zinc in more 

than about 75 percent of the black shale samples of sets 1, 2, and 4.
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E27

However, at the 95-percentile level, the content of zinc is relatively 

high in all sample sets, ranging from 0.05 percent in set 2 to 0.3 percent 

in set 3. Were analyses available for all samples, they would probably 

indicate zinc to be one of the more characteristic elements of metal-rich 

black shale. Visual inspection of the analyses indicates that a high 

content of zinc frequently corresponds with a high content of such 

elements as vanadium, molybdenum, chromium, and nickel. Zinc 

probably occurs commonly in a separate mineral form, such as sphalerite, and is not directly attached to or associated with the organicmatter fraction of the rock. In this respect, zinc probably behaves 

much as does iron in pyrite.

ZIRCONIUM

The median content of zirconium ranges from 0.003 percent in 

samples of set 3 to 0.007 percent in samples of sets 1 and 4. The 

median zirconium content varies among the four sets of samples in a 

manner similar to that of titanium. Zirconium, like titanium, varies 

directly with aluminum in the first three sets, but not in set 4. However, neither a mafic source nor biogenic precipitation provides a 

suitable explanation for the relatively high zirconium in set 4; so this 

problem is unresolved. A strong positive correlation between zirconium and titanium was 'found in the first three sample sets, and 

between zirconium and gallium, sodium, scandium, magnesium, potassium, aluminum, and strontium in set 3. Zirconium also has a strong 

negative correlation with calcium in set 1 and with carbon in sets 

2 and 3. Zirconium is one of the most characteristic elements of the 

detrital-mineral fraction of black shale.

SUMMARY AND CONCLUSIONS

1. A comparison of the analyses of core samples (set 1) with a similar 

set of samples collected in outcrops (set 2) reveals a significant 

difference in concentration of several elements that may be attributed to their relative susceptibility to weathering, leaching, and 

removal from the outcrop and subsequent concentration either in 

pore water or as a separate mineral precipitate at depth. The 

elements involved probably are sodium, potassium, manganese, 

iron, and cobalt.

2. Many elements tend to occur chiefly in either the detrital-mineral 

fraction, the organic-matter fraction, or the chemically and biogenically precipitated fraction. An element may occur at low 

concentration in all fractions of one set and at high concentration 

in one or more fractions of another set. The following groupings 

are admittedly based on incomplete correlation data and on esti-
E28 CONTRIBUTIONS TO GEOCHEMISTRY

mates of the major mineral constituents of black shale, and so 

should be regarded as provisional.

A. Elements primarily associated with the detrital-mineral fraction of black shale include silicon, aluminum, magnesium, 

iron (in part), sodium, potassium, titanium, manganese, barium (in low concentration), gallium, lanthanum, lead, scandium, strontium (in low concentration) and zirconium. 

B. Elements primarily associated with the organic-matter fraction 

of black shale include silver, beryllium, boron(?), cobalt, 

chromium, copper, molybdenum, nickel, vanadium, and 

yttrium (?). Most of these elements are probably fixed or 

sorbed by the decaying organic matter at or a short distance 

below, the sediment-water interface at the time of accumulation. Some of them may be released, mobilized, and recombined in new ways as a result of the chemical changes that 

take place in the organic matter after burial. For example, 

magnesium-bearing chlorophyl pigments in recent sediments 

give way with increasing depth to vanadium and perhaps 

nickel compounds (Abelson, 1963). This change occurs at 

low temperatures in less than a few thousand years. It seems 

possible that part of the vanadium may also combine with 

such clay minerals as illite to form a clay mineral analogous 

to roscoelite mica.

C. Elements primarily associated with the chemical or biogenically 

precipitated mineral fraction include iron (in part), calcium, 

boron(?), strontium (in part) yttrium(?), and zinc. In 

addition, silicon in the eugeosynclinal shales is mostly 

chemically or biogenically precipitated. Thus, elements included in this group comprise the major mineral constituents of siliceous and calcareous shells. Strontium occurs in 

minor amounts in calcareous shells, and the elements iron, 

zinc, and barium form discrete sulfide or sulfate minerals 

associated with or replacements of microorganisms and fecal 

pellets. Boron and yttrium are included in this group, 

although without adequate criteria to exclude the possibility 

that they may also be associated with the organic-matter 

(fraction.

3. Remarkably similar suits of minor elements are concentrated at the 

95-percentile level of samples from both the shelf and eugeosynclinal environments. These elements are mainly those associated 

with the organic-matter fraction of the black shale or are biogenically precipitated; therefore, they may be regarded as characteristic of metal-rich black shale. They are listed here in approxi-
ELEMENT DISTRIBUTION IN SOME BLACK SHALES E29

mately decreasing frequency of occurrence: vanadium, zinc, 

chromium, nickel, silver, barium, molybdenum, cobalt, yttrium, 

boron, and copper. Significant differences between the samples 

from the shelf environment and the samples from the eugeosynclinal environment are apparent, however. Molybdenum and 

nickel are relatively much more concentrated in the samples from 

the shelf environment, and barium is relatively much more concentrated in the samples from the eugeosynclinal environment. 

4. Any future consideration of black shale as a potential commercial 

source of the contained metals would need to evaluate the following geologic factors.

A. The Pennsylvanian black shale beds in the Eastern Interior 

coal province are thin and comprise only a small part of the 

sedimentary sequence, but individual beds are flat lying and 

because they are locally removed during strip coal-mining 

operations, the cost of recovery would thereby be reduced. 

. B. The Ordovician and Silurian graptolitic black shale beds in 

the western eugeosynclinal region are locally thick, but the 

enclosing strata are almost everywhere so intensely deformed 

that systematic prospecting according to their stratigraphic 

position would pose difficult problems in correlation.

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