Conodont Color Alterationan Index to Organic Metamorphism 

By ANITA G. EPSTEIN, JACK B. EPSTEIN, and 

LEONARD D. HARRIS 

GEOLOGICAL SURVEY PROFESS I ONAL P A P ER 995 

Experimental and fi eld studies 

showing the application of conodont 

color alteration to geothernwmetry_, 

m etamorphism, and structural geology 

and for assessing hydrocarbon potential 

UNITED STATES GOVERNlVIENT PRINTING OFFICE, ' 'V'ASHINGTO N 197 7 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Epstein , Anita G 1937-

Conodont color alteration--an index to organic metamorphism. 

(Geological Survey professional paper; 995) 

Bibliography: p. 

Supt. of Docs. no.: I 19.16:995 

1. Conodonts. 2. Paleontology--Paleozoic. 3. Paleontology--Appalachian Mountains. 4. Geological time. 

5. Earth temperature . 6. Metamorphism (Geology). I. Epstein, Jack Burton, 1935- joint author. 

II. Harris, Leonard D., joint author. III. Title. IV. Series: United States. Geological Survey. Professional 

paper; 995 . 

QE899.E66 562 76-608130 

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

Washington, D.C. 20402- Price $1.10 (paper cover) 

Stock No. 024-001-02856-5 
FIGURE 

CONTENTS 

Page 

Abstract --------------------------------- ------------------------------------------------ 1 

Introduction ---------------- ------------------- ------------- --- --------------------------- 1 

Experimentally induced color alteration _ _ _____ __ _ ___ _ _ ___ _ ___ __ _ ____ _____ _ __ __ _ __ _ _ ___ __ _____ 3 

Open-air heating runs ___ --: - ________ __ ______ _____ _______ __ __ l_ _ ___ __ _ ___ _ ___ __ _ __ _ _ _ __ __ 4 

Determination of color alteration index (CAl) ____________ __ __ j________ __ _________________ 4 

Does pressure affect color alteration? ------ - - --- - --------------------- ----------- ------- 9 

Evaluation of experimental data using field collections of conodonts ---- ------------------------- 10 

CAl as a geothermometer --- - ----------------- - - -------- --------- - - - - ------------------ 10 

Do tectonics influence color alteration or carbonization?------ - - ------------------- ------- 10 

Correlation of conodont CAl with other organic maturity indexes - - ------------ --------------- 12 

Effects of host rock on organic metamorphism ----- ------------ - - ---- ---------------- -------- 14 

Field evaluation and application of conodont CAl -------------- --- --- ---------------- -------- 15 

Ordovician CAl isograd map ----- ------------ ------------ --- - - ------------------------- 16 

Silurian through Middle Devonian CAl isograd map------- - ----------- ------------------ 18 

Upper Devonian through Mississippian CAl isogr ad map ----------------------- --------- 18 

CAl isograds provide cutoffs for occurrence of h ydrocarbons --- ----- ----- ----------------- 22 

Conclusions ---------------------------------------- - - - -------------- --------------- --- ---- 25 

Acknowledgments ------------ - - - - ------------------------- ---- ---- ------------------------ 25 

References cited ------------------------- - - - ----------- -------- ---------- ----- ------------ 25 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

16-20. 

ILLUSTRATIONS 

Photograph showing conodont elements of diverse form, ager and color ------------------------ --

Photograph of unaltered conodont elements used in heating experiments ----------------- ---------

Ahrrenius plot of h eat-induced, open-air, conodont color alter ation data --------------------------

Photograph showing experimentally alt ered conodonts of a ll color alteration indexes _______________ _ 

Chart showing experimentally produced and naturally cc ur~i g colors in conodonts and the geologictemperature and fixed-carbon range for each CAL ___ __ l_ ______ ____________ _______ ____ _____ _ 

Photograph showing expe-rimentally produced pale-yellow to black to crystal-clear conodonts ____ __ _ 

Photograph showing conodonts from chlorite- t o garnet-grade metamorphic facies __________ ______ _ 

Chart showing CAl fo~ :onodont~ subject ed to different pressl1res and chemical environments while under the same cond1twns of time and t emperature ____ ___ ___ _____ ______________________ ______ _ 

Ahrrenius plot of experimental data showing m ethod of corhputing maximum host-rock temperature 

using conodont CAl ________ ____ __ _______ _________ ____ __ __ ___ ___ _____ __________ - - - --------

Map showing selected localities for Early and early Middle Devonian conodonts in part of the Appalachian basin and their known overburden --- - ------ --- ---- -------------------------- ------

Chart showing correlation of three optical organic metamorphjism indexes ____ ____ ________________ _ 

Chart showing age and thermal r ange and relative cost of three optical organic metamorphism indexes ------ ------- - - ----------- ---------- - - - --- ------------------------- ------ --------- Map showing CAl isograds for Ordovician con odont localities in the Appalachian basin ____ ________ _ 

Maps of the West Virginia-Virginia border a ea showing isograds supPrimposed on maximum isotherms for hot springs --------------- ----------- ----- -------- --------------------- ------

Map showing major thrust faults and localities for some Middle and Late Ordovician conodonts from 

eastern T(mnessee __ ___ ____ _____ __ ___ ______ ______ _____ _____ ___ ___________ __ ___ ___________ _ 

Maps of the Appalachian basin showing : 

16. CAl isograds for Silurian thr ough Middle Devonian 1

rocks --- ------------ ---- ------- ------

17. CAl isograds for Upper Devonian t hrough Mississippian rocks and the eastern limit of oil and 

gas fields - - - - - - ------------ ------------- - ---- - - ---- --- ---------- ----------------- 18. Upper Mississippian CAl isograds superimposed on isopachs for Pennsylvanian rocks _____ _ 

Tll 

Page 

2 

3 

4 

5 

6 

7 

8 

9 

11 

12 

13 

14 

16 

18 

19 

20 

21 

22 
IV CONTENTS 

Page 

FIGURES 16-20. Maps of the Appalachian basin showing- Continued 

19. CAl isograds for Ordovician rocks and t he eastern limit of oil and gas fields ______________ 23 

20. CAl isograds for Silurian through Middle Devonian rocks and the eastern limit of oil and gas 

fields ------------------- ----------------- ------------------------ --------------- 24 

TABLE 

Page 

TABLE 1. Munsell soil colors l()f conodont color alteration indexes------------------------------------------- 5 

Metric unit 

millimetre (mm) metre (m) 

kilometre (km) 

square metre (m~) 

squar e kilometre ( km2) 

hectare (ha) 

cubic centimetre (em': ) 

litre (l) 

cubic metre (m ) 

cubic metre cubic hectometre (hm':) 

litre 

litre 

litre 

cubic metre 

cubic metre 

gr am (g) 

gram 

tonne (t) tonne 

kilogram per square 

centimetre (kg/ cm2) 

kilogram per squarr 

centimetre 

eubic metre per· seconrl 

(m3js) 

METRIC-ENGL.ISH EQUIVALENTS 

English equivalent :\Ietric unit English equ ivalent 

Length Specific combinations-Continued 

o.o:-m;n inch (in) 

:;.:! feet ( ft) 

.62 mile (mi) 

Area 

10.76 

-~86 

2.47 

Volume 

0.061 

lil.O:: 

3::J.:n 

.0008 1 =i-:10.7 2.11:: 

1.06 

.:w 

.OOO:!H 

H.:wo 

Weight 

o.o:~ii 

.00:!:! 

1.1 

.ns 

square feet (ft2) 

square mile (mi2) acres 

cubic inch (in ) 

cubic inchr,: 

cubic feet (ft3) 

acre-foot (acre-ft) 

HCL'P-feet 

pints (pt) 

quarts (qt) 

gallon (gal) 

rnillion galiom; (.:IIgal or 10° ga l) harr·p],; ( hhl ) (1 hh1=42 ,!.:HI) 

Oll ll('P. aYoirdupois (or. :t\d)') 

pound, a Yoirdupois (lh awlp) 

tons, ;;hort ( 2.000 l h) 

ton, loug (2,240 lb ) 

Specific combinations 

O.!lfl 

.!Ii-I 

atrnospherP (atm) 

har· (O.!lf'fi!l atm) 

c:ubic feet v~t· sceon<l (ft':/ ,:) 

litre per second (1/ s) 

cubic metre per second 

per square kilometre 

[ (m3/ s) / km2 ) 

metre per day (m/ d) 

metre per kilometre 

(m/km) 

kilometre per honr· 

(km/ h) metre per second (m/ s) metre squared per day 

(m2/ d) 

cubic metre per second 

(m3/ s) 

cubi c metr e per minute 

(m3 /min ) 

litr e per second (l/s) 

litre per second pf'r metre [ (1/~'>) / m 1 

kilometre pe r hour 

(km/ h) metre per seco nd (mj,:) 

gram per cubic 

centimetre (g/rm::) 

l!l'am per ~'>qua re 

ecntimetn• (_g r·nt~) 

:,:-ram per squan• eentimetre 

llf'gree CelsiuH ( •r.) 

rkl!rees Ceh;ius 

(tPBIJ!f'I'Ht UrP ) _____________ _ __:_ _ __ ----- ---·---- --

.0353 cubic foot per second 

!ll.--17 cubic feet p er seco nd per 

square mile [ (ft3/s) / mi2 ) 

:::.28 feet per day (hydraulic 

conductivity) (ft/d) 

;;_2S feet pe r mile (ft/mi) 

.9113 foot per second (ft/s) :1 .2S feet per second 

10.764 feet squared per clay (ft2/d) 

(transmissivity) 

= 22.826 million gallons per day (Mgal/d) 

= ~64.2 gallons per minute (gal/ min) 

13.8() ~allons per minute 

4.S::I gallons per minute per foot 

[(gal/ min) /ftl 

.6:! mile per hour (mi/ h) 

2.2:::7 miles per hour 

li:!.-t:: poun<l,: 1wr euhif' foot (lh/ft::) 

~.O-!S pountb Jl<'l' square foot (lh/ ft2 ) 

.0142 pound per square inch (lb/in2) 

Temperature ----------------------- l.S rtegrees Fahrenheit ( •F) 

= L (1.8 X •c) + H2) degrees Fahrenheit 
CONODONT COLOR ALTERATION-AN INDEX TO 

ORGANIC METAMORPHISM 

1---

By ANITA G. EPSTEIN) JAcK B. EPSTEIN) and LEONARD D. HARRIS 

I ____ _ 

ABSTRACT 

Field and laboratory experiments show that color alteration in conodonts is directly related to the depth and duration of burial and the geothermal gradient and corr late s 

with fixed carbon, vitrinite reflectance, palynomorph tr anslucency, and isopach data. Five progressive and irreve~·sibl e 

color changes ranging from pale yellow to black are discriminated. Compilation of color alteration index (CAl) maps for 

limestones of several ages in the Appalachian basin show : 

(1) a general systematic change from pale yellow (CAI=1) 

tO black (CAI=5) from west to east; (2) within a structural 

belt, aider conodonts are darkest; ( 3) fixed carbon values 

determined from coals cannot be directly applied to carbonate 

rocks; ( 4) several areas of anomalously low CAl values in 

windows exposing Ordovician rocks within the Blue RidgePiedmont terrane. 

All field colors were reproduced by controlled high-temperature (300°-600° C) long-term (10-50 days) runs in open air 

with and without water. These data show: ( 1) color alteration of conodonts is time and temperature dependent; (2) the 

sequence of color change from pale yellow to black found in 

field collections is the same as that produced by heating alone; 

(3) upper and lower geologic temperature limits for each 

CAl determined from a log time versus reciprocal of absolute 

temperature plot. Experiments at high temperature (550° C), 

confined pressure ( 1 kbar) , with and without water, using 

methane (reducing) and argon (inert), indicate that wate1· 

in combination with confined pressure retards color alteration. 

The color alteration of conodonts is a valuable tool for assessing organic metamorphism because it is a rapid and inexpensive method requiring only standard laboratory techniques and a binocular microscope. Standards can be easily 

assembled and reproduced. The technique does not provide 

thermal thresholds for oil generation, but does provide thermal 

cutoffs for oil, condensate, and dry gas generation. Conodont 

color alteration begins near the upper thermal limit for the 

preservation of many palynomorphs. Moreover, conodonts are 

most abundant and most easily concentrated from marine carbonate rocks in which palynomorphs generally are poorly preserved and in which vitrinite is least abundant and commonly 

absent. 

INTRODUCTION 

In the last two decades, geochemists, coal petrologists, and even micropaleontologists have added an 

instrumental and chiefly microscopic sophistication to 

the application of David White's ( 1915) carbonratio theory. Light transmission and reflectance 

measuremenus of palynomorphs and coaly particles, 

as well as pyrolysis and gas chromatography of organic matter are now standard petroleum and coal 

industry techniques for assessing organic maturity 

(see Bostick, 1974; Castano and Sparks, 1974; 

Gutjahr, 1966; Martin and others, 1964; Patteisky 

and others, 1962; Staplin, 1969). This study adds 

a new index, the conodont, to the growing list of 

indicators of organic metamorphism. Our technique, 

moreover, is inexpensive and rapid and is applicable 

to rock types and to age and thermal r anges that are 

not readily analyzed by other methods. Until now, 

we have presented only preliminary evaluations of 

this technique (Epstein and others, 197 4, 1975a, b; 

Epstein, 1975). 

In the last 15-20 years, conodonts have become 

one of the dominant fossil groups for biostratigraphy and worldwide correlation within most of 

their geologic range (for example, Sweet and Bergstrom, 1971). This study increases their use from 

index fossils to metamorphic indexes and demonstrates their application to geothermometry, metamorphism, structural geology, and for assessing oil 

and gas potential. 

Conodonts, which are the microscopic hard parts 

of an unknown organic group, are commonly 0.1 to 

1 mm in size (fig. 1). Several individual conodonts, 

in most cases, of different shape or form, belonged 

to one conodont apparatus or conodont-bearing organism (for example, all form elements in fig. 4, 

column 1.5). Conodonts have a worldwide distribution in most marine rocks of Cambrian through most 

of Triassic age, although their abundance varies considerably. Where deposition was rapid, conodonts 

may be absent or as rare as 1-2 per kilogram; 

where deposition was slow, there may be several 

thousand per kilogram. They are readily recovered 

from mud-drilled cuttings but are generally not re1 
2 CONODONT COLOR ALTERATION 

0.2 mm 0 

CONODONTS 

1. Microfossils (generally 0.1.-1 mm). 

2. Hard parts of an unknown organic group. 

3. Several conodont elements belonged to one organism. 

4. Range--Cambrian thru Triassic. 

5. Worldwide distribution in most marine rocks. 

6. Mineral composition-carbonate apatite. 

7. Color-pale yellow, brown, black, opaque white, and crystal clear. 

FIGURE 1.-A selection of conodont elements of diverse form, age, and color and some generalizations about conodonts. Specimens shown in figures m-o were kindly given to us by H. P. Schonlaub, Geological Survey of Austria. 

coverable from air-drilled cuttings which are usually 

finer than the lower size limit of determinable conodonts. Most important for our purposes is their 

mineral and chemical composition. Conodonts are 

essentially carbonate apatite, and approximate the 

mineral francolite (Pietzner and others, 1968, p. 

124, show the bulk formula as Ca,-,Nao.l l (PO~) :1.01 

(CO:,) o.1nF o , :, ( H20) o. :-r.). Thus they can be easily extracted fro carbonate rocks by acetic- or forrnicacid treatment and concentrated with heavy liquids 

and (or) a magnetic separator. Because of their 

mineral composition, they ·readily persist into greenschist metamorphic terranes and have even been 

recovered from marbles interbedded with garnetmica schists (H. P. Schonlaub, written and oral 

communs., 1974). Unweathered conodonts are pale 

yellow (fig. la-d), light to dark brown (fig. le--j), 

black (fig. lk, l), opaque white (fig. lm), and crystal clear (fig. ln, o). If unweathered and unaltered, 

they are pale yellow to light amber (fig. la-d). 

Unweathered conodonts from thin undisturbed 

cratonic sequences are generally pale yellow (fig. 

la-d), and those from thick geosynclinal sequences 

that also happen to be complexly deformed are 

light to dark brown (fig. l e-j), black (fig. llc, l), 

opaque white (fig. lm), and crystal clear (fig. ln, o). 

In 1944, Ellison reported that conodonts heated 

in a closed tube give off water and turn dark gray. 

Two decades later, Lindstrom (1964) correctly attributed this color alteration to a carbon-fixing process. Trace amounts of organic matter, probably 

amino acids, were reported from demineralized 

conodonts by Pietzner and others ( 1968). The basal 

part of the conodont element, which is very well 

laminated, contains higher concentrations of organic 

material than the denticles. It appears that organic 

matter is one of the chief contributors to conodont 

color. 

Until now, color alteration in conodonts has not 

been systematically mapped nor explained, even 

though earlier conodont workers noted these color 

changes. We have evaluated these color changes by 

using field data-that is, by mapping conodont color 

throughout the Appalachian basin, and in laboratory 

experiments by inducing color alteration. 
EXPERIMENTALLY INDUCED 3 

EXPERIMENTALLY INDUCED COLOR 

ALTERATION 

The literature concerning diagenesis of organic 

matter emphasizes heat and time as the dorninant 

factors in carbonization and thus color alteration (see 

for example, Abelson, 1954; Philippi, 1965; Teichmtiller and Teichmtiller, 1968; Bostick, 1973 ; Hood 

and others, 1975) . 

In the experiments, we used conodonts from the 

Kope Formation of Late Ordovician age fom northcentral Kentucky. Conodonts from this limest one a r e 

especially well suited for this purpose because, they 

are abundant (about 5,000 per kilogram), well preserved, and among the lightest colored in the Appalachian basin (fig. 2). Their pale-yellow color reflects the fact that these conodonts have had a minimal thermal history because they were never buried 

by more than 2,000-3,000 feet (610-910 m) of overburden, and t here are no structural or intrusive 

complications at the collecting locality. Figure 2 

shows, however, that even an unaltered assemblage 

of conodonts has some color variation which is related to the maturity and (or) robustness of the 

individual element. Larger, thicker (fig. 2c, d), or 

adult (fig. 2a, d ) elements are darker colored than 

thin (fig. 2/, g ) , delicate (fig. 2h), or juvenile (fig. 

FIGURE 2.-Some Late Ordovician conodont elements from the Kope Formation of north-central Kentucky. These are among 

the lightest (pale yellow) conodonts in the Appalachian basin and were used t o st udy the effects of experimental metamorphism on conodont color alteration. The collecting locality ( 60G81) and conodonts are described in Bergstrom and Sweet 

(1966). Lettered conodonts are discussed in the text. 
4 CONODONT COLOR JALTERA TION 

2b, e) elements because the larger conodonts have 

more lamellae and thus more interlamellar spaces 

containing organic matter. 

OPEN-AIR HEATING RUNS 

The pale-yellow conodonts were heated in an electric furnace, in covered porcelain crucibles, in air, 

at 50 ° C-increments from 300°-600° C and from 10 

to 50 days. Specimens were pulled at regular intervals so that there is a permanent record of color 

change. Figure 3 is an Ahrrenius plot of the data. 

The experiments showed that: 

1. The sequence of color change from pale yellow 

to black found in field collections is the same 

as that produced by heating alone. 

2. Color alteration is progressive, cumulative, and 

irreversible. 

3. Color alteration is time and temperature dependent. At 300° C, color alteration begins after 

350 hours of heating; at 400 ° C, after 5 hours 

of heating; at 500 ° C, after only half an hour 

of heating. 

4. A comparison of the experimental data with field 

collections indicated that five color intervals 

could be readily discriminated. These are numbered and termed color alteration indexes 

(CAI). 

DETERMINATION OF COLOR ALTERATION INDEX 

(CAl) 

Figure 4 shows experimentally altered conodonts 

that represent all CAI values. It is mainly the basal 

pale yellow to amber part of the unaltered conodont 

el ment that changes color. The white matter, which 

5X10 -------------- ------------ ------~------ ------------------------~ 

(/) 

0::: 

108 

106 

~ 105 

>-

z 

-_ 104 

UJ 

~ 

~ 

103 

102 

10 

50 

RANGE OF CONODONTS 

(/) 

0::: 

::J 

100 0 

:I: 

~ 

ui 

~ 1-

100 150 200 

RECIPROCAL OF ABSOLUTE TEMPERATURE RECALIBRATED IN oc 

FIGURE ~.-Ahrrenius plot of the heat-induced, open-air, conodont color alteration data. Vertical bars represent duration of 

heatmg runs at constant temperature. For the 300°- 400° C runs, conodonts we~e pulled every 24 hours; for higher tempe.rature r~ns, conodonts were pulled every half hour or hour for the first 24 hours and at 24-hour intervals thereafter. 

Diagonal hnes bound color alteration index (CAl) fields. 
EXPERIMENTALLY INDUCED 5 

1 1.5 2 3 4 5 

FIGURE 4.-Late Ordovician conodont elements showing experimentally induced color alteration. CAl given at top of each 

column. Most of the conodonts shown are phragmodiform, dichognathiform, and oistodiform elements of Phragmodus undatus Branson and Mehl. 

is nearly confined to the denticles, is generally unaltered up to CAl 4 (fig. 4) ; beyond CAl 4, the 

denticles become crystal clear, gray, or black. 

At CAl 1, conodont color is assumed to be unaltered, and conodonts are generally pale yellow. 

(Colors were determined from Munsell soil color 

chips (fig. 5 and table 1) .) Very pale brown conodonts mark the beginning of color alteration (CAl= 

1.5, fig. 4). CAl 2 is brown to dark brown, and so 

on to CAl 5 which is black. Each CAl is distinctive 

enough that half indexes frequently may be determined (see fig. 9.) 

To ensure consistent indexing, sets of standards 

were assembled using induced color alteration specimens as well as conodonts from field collections. 

Figure 5 is a color chart for CAl determination. 

TABLE 1.-Munsell soil colors of conodont color alteration indexes 

fSeveral form elements of each color alteration index from field collec- - tions and laboratory experiments were matched to Munsell soil color chips 

(see fig. 5) (Munsell Color Company, 1971)] 

Conodont 

alteration Munsell soil color jndex 

1 Pale yellow (2.5Y7 I 4 to 8/ 4). 

11;2 Very pale brown (10YR7/3 to 10YR8/4). 

2 Brown to dark brown (10YR4/2 to 

7.5YR3/2). 

3 Very dark grayish brown (10YR4/2) to dark 

reddish brown (5YR2.5/2) /to black 

(10YR2.5/1 ) . 

4 Black (5YR2.5/1) to black (10YR2:.5/1). 

5 Black (7.5YR2.5/0) to black (2.5YR2.5/0). 

1 Color not shown in figure 5. 

Any collection of conodont elements shows variation in shape and size and thus color; we generally 
, 6 CONODONT COLOR ALTERATION 

1 

2 

3 

4 

5 

<60% 

55% 

to 

70% 

70% 

to 

80% 

80% 

to 

95% 

+95% 

FIGURE 5.-(For explanation see facing page.) 

determine the alteration index from the lightest 

colored elements or parts of elements. If only robust elements are resent, CAl is determined on 

the thin edge of an element. The same procedure 

is used in determining palynomorph translucency, 

where wall thickness, ornamentation, or reworking 

produce similar variations in color in a palynomorph 

assemblage ( Staplin, 1969). 

Naturally occurring conodont collections that 

have a CAl of 4.5 or higher, show changes in surface texture as well as color. At these high indexes, 

conodont surfaces change from smooth and vitreous 
EXPERIMENTALLY INDUCED 7 

FIGURE 6.-N aturally occurring pale-yellow (CAl 1) and heat-induced dark-brown (CAl 3), black (CAl 5), gray (CAl 6) ~ 

opaque white (CAl 7), and nearly crystal-clear (CAl 8) phragmodiform elements. CAl 8 was produced by heating paleyellow conodonts wrapped in platinum foil in an open-air electric furnace at 950° C for 4 hours. 

FIGURE 5.-Cha,rt showing experimentally produced and naturally occurring colors in conodonts and the geologic-temperature and fixed-carbon range for each CAL 

The shape and size of conodonts aff.ects their color. Even 

though the experimental conodonts shown are all form elements of Phragmodus undatus Branson and Mehl, there is 

still some .range in color within each index because of the 

robustness or delicateness of the various specimens. If, howev·er, the same form element is compared for all indexes (for 

example, the thin bar fragment of the phragmodiform element in the lower right of each box), the index sequence is 

obvious. Robust elements should not be compared with delicate elements. Note too that once CAl 5 is reached, all morphotypes are black. In center column, specimens labeled D 

are Devonian, all others are Ordovician. Specimens shown in 

the column for CAl 1.5 are mostly robust hyaline forms 

(elements that virtually lack white matter) and therefore appear darker than many conodonts of slightly higher index. 

The temperature ranges are from the Ahrrenius plot of the 

experimental data (fig. 3). These ranges cover durations 

of 1 million to 500 million years. The higher temper ature 

value is therefore extreme and in most geologic situations 

the temperature determination would be near the lower end 

of the temperature range (the method for temperature determination is shown in fig. 9). The fixed carbon values are 

from refl.ectance determinations on vitrinite obtained from 

the same field samples as indexed conodonts. The color 

range for each CAl is also shown by Munsell soil color 

chips, color values are given in table 1. 

to pitted and grainy. The high temperatures that 

produce these high indexes undoubtedly also promote corrosion of the conodont surface. 

We are now in the process of extending the color 

chart (fig. 5) into higher temperature ranges. With 

continued heating, black conodonts become gray, 

then opaque white, and in the last stage before decomposition, crystal clear (fig. 6). We believe· that 

the fixed carbon of the black conodont is driven out 

of the conodont element (volatilized) at these high 

temperatures, thus clearing the conodont element. 

The change from opaque white to crystal clear 

conodonts may result from the release of water of 

crystallization (see "Introduction," this report, for 

bulk chemical formula) as well as from recrystallization. 

Recently (1974), conodonts have been recovered 

from increasingly higher grade regional metamorphic facies in the Austrian Alps b(Y H. P. Schonlaub, Geological Survey of Austria (written commun., 1974). We gratefully acknowledge his adventuresomeness in processing these high-grade 

carbonates for conodonts and for allowing us to use 

his specimens in our study (fig. 7) . Thermal alteration and metamorphic grade increase from left to 
8 CONODONT COLOR ALTERATION 

5 6 7 8 

0.2 .mm 

FIGURE 7.-Conodont elements from carbonate rocks within chlorite- (CAl 5) through garnet- (CAl 8) grade metamorphic 

facies in the Austrian Alps. CAl 5 and 6 specimens are from Lower Silurian carbonate rocks interbedded with slates at 

Radmer, Austria, and are from collections about 100 m apart; CAl 7, from lower Middle Devonian carbonate rocks, Styria, 

Austria; CAl 8, from Upper Silurian marbles interbedded with garnet-mica schists, serpentinites, and amphibolites, Salzburg, Austria. 

right (fig. 7), from black (chlorite grade), to gray, 

to opaque white, and finally crystal-clear conodonts 

from marbles interbedded with garnet-mica schists, 

serpentinites, and amphibolites. We produced nearly crystal-clear conodonts in the laboratory by heating at 950° C for 4 hours (fig. 6, column indexed 8.). 

Schonlaub has noted (written commun., 1974) that 

the two collections from Radmer, Austria, although 

only 100 m apart, have conodonts of very different 

color; black conodonts (CAl 5) were recovered from 

black platy carbonate rock interbedded with black 

slates (fig. 7); gray to opaque white (CAl 6) conodonts were recovered from light-gray carbonate 

rock (fig. 7). Schonlaub suggests that the different 

host and (or) adjacent rock at this locality may be 

affecting conodont color alteration. Schonlaub also 

states (written commun., 1974) that other samples 

only a few metres apart from the Styrian "Erzberg," contain black, gray, opaque white, and transition (column 6 lower specimen) conodonts. The 

black to gray to opaque white transition may be 

very short lived. CAl 6 may overlap the upper and 

lower temperature ranges of CAl 5 and CAl 7, 

respectively. 

In addition, we sampled several localities in the 

western United States where carbonate rocks containing pale-yellow conodonts are intruded by small 

dikes or sills or are in contact with lava flows. At 

each locality the thermal effect of the intrusive or 

extrusive body was recorded by conodont color alteration; conodonts changed from white to black to 

brown to pale yellow with increasing distance from 

the igneous body. 

The alteration index of conodont elements can be 

determined by any of the following procedures: 

1. Starting with pale-yellow conodonts, a set of 

standards can be cooked in open air in an 

electric furnace using the following recipe: 

CAl= 1.5, heat for half an hour at 500° C. 

CAl= 2, heat for 3 hours at 500° C. 

CAl= 3, heat for 14 hours at 500° C. 

CAl= 4, heat for 8 hours at 550° C. 

CAl= 5, heat for 48 hours at 600° C. 

Clusters of each laboratory-produced index are 

then placed on a clear glass slide overlying 

a ground glass plate. The unknowns can then 

be placed amid or adjacent to each cluster; a 
EXPERIMENt ALLY INDUCED 9 

best match is determined under a binocular 

microscope using unfiltered reflected light. 

2. A set of standards can be assembled frorn field 

collections. Then follow the procedure outlined 

in 1. It is helpful to have several sets of standards representing conodonts of different ages 

and morphotypes. 

3. The Munsell soil color chips given for each index 

in table 1 can be mounted in sequence on gray 

mounting board. The conodonts are placed on 

the gray board adjacent to the chip and 

matched under a binocular microscope. 

4. The conodonts shown on the color chart (fig. 5) 

can be cut out and placed in sequence on gray 

mounting board. CAl value can then be determined using the same procedure as in 3. 

If conodonts cannot be freed from their matrix 

(conodonts exposed on bedding plane of clastic rock 

or chert), the CAl value may be crudely determined 

by placing conodont standards on the host rock adjacent to the embedded conodont and select ing a 

best match. 

DOES PRESSURE AFFECT COLOR ALTERATION ? 

The long-term experiments showed that conodonts 

heated at 550 ° C for 3 hours in open air have a CAl 

value of 3 (figs. 3, 8) .Using argon and then methane 

as pressure media, the Kope Formation conodonts 

(fig. 2) were sealed in platinum capsules and heated 

at 550 ° C for 3 hours at 1 kilobar (kbar) in bombsthe CAl value was the same as in open air (fig. 8). 

Confined pressure and anoxic conditions neither retarded nor accelerated carbonization. Huck and 

Patteisky ( 1964) showed similar results involving 

experimental metamorphism of coal. They reported 

an increase in rank from 67 to 82 percent fixed carbon for coal heated in a vacuum at 350° C and that 

the same coal heated at the same temperature, but 

at 8,000 atmospheres still maintained the 67 to 82 

percent change in fixed carbon. Bostick ( 1970) also 

reported no change in vitrinite reflectance of phytoclasts from runs in which temperature was kept 

constant and pressure was varied from 260 to 1,650 

bars. Mcintyre (1972), however, in his study on the 

effect of experimental metamorphism on pollen in a 

lignite, stated that his experiments showed that 

pressure retards carbonization. Unfortunately his 

data ( 1972, table 1) do not appear to support his 

conclusion. 

The Kope Formation conodonts were next heated 

in open air in an electric furnace having a continuous 

550° C FOR 3 HOURS 

PRESSURE GAS CAl 

1 atm Air 3 

WITHOUT 

WATER 1 kbar Argon 3 

1 kbar Methane 3 

FIGURE 8.-Chart showing CAl for conodonts subjected to different pre-E,sures and chemical environments while under the same conditions of time and tempe-rature. 
10 CONODONT COLOR ALTERATION 

water-vapor feed. All conodont pulls had the same 

CAl values as conodonts heated under the same conditions of time and temperature, but without water. 

Using argon and then methane as pressure media, 

conodonts were sealed in platinum capsules containing distilled water. The conodonts recovered after 

3 hours of 550° C heating at 1 kbar had a CAl of 

1.5 (fig. 8). Thus, in a sealed system, water in combination with confined pressure and heat considerably retards carbonization. Consequently, the open-air 

experimental temperature data cannot be applied 

to wet sealed systems at relatively high pressure, 

simply because, the temperature determinations 

would be too low. The assessment of the organic 

maturity, however, would still be accurate. This 

helps explain oil production at anomalously high 

temperatures from overpressured rocks. 

EVALUATION OF EXPERIMENTAL DATA 

USING FIELD COLLECTIONS OF CONODONTS 

CAl AS A GEOTHERMOMETER 

Conodonts from Monterey, Va., in the Valley and 

Ridge province, were compared with our standards 

and were determined to have a CAl value between 

4 and 4.5. The conodonts are of Middle Ordovician 

age; thus the maximum possible time for burial and 

heating could be as long as 470 m.y. One can, however, impose a few time limits from a knowledge of 

Appalachian geology. The Middle Triassic is the 

latest possible time for beginning of unloading by 

erosion in this part of the Appalachian basin. Therefore, 270 m.y. is the maximum possible time for 

burial and heating, thus providing the lowest possible temperature for conodonts of CAl 4-4.5 (fig. 

9, heavy solid lines). Projecting the 4-4.5 field segment of the 270 m.y.-line to the x axis yields a temperature range of 185°-220° C for these conodonts. 

If, however, unloading began in the Late Pennsylvanian, which is the earliest possible time for unloading in this part of the basin, the maximum time 

for burial and heating is 210 m.y. (fig. 9, dashed 

lines), thus a maximum temperature range of 190°-

2300 C. This temperature range is very close to the 

first determination, showing that time becomes less 

important beyond durations of about 50 million 

years. 

Are these calculated temperatures compatible 

with field geologic data? In the vicinity of Monterey, 

at least 14,300 feet ( 4,770 m) of rock is known to 

overlie the Middle Ordovician (fig. 9). Assuming 

an average geothermal gradient of 1 o C per 100 

feet, known overburden alone can account for a temperature of 160° C. In the calculation we have not 

taken into account the thickening of section by folding and faulting, nor have we tried to completely 

restore missing section. In spite of this, the temperatures determined from the Ahrrenius plot are 

compatible with isopach data. Moreover, Paleozoic 

rocks in the Monterey area are cut by Cenozoic intrusions. The additional 30°-70° C can easily be accounted for by a higher than average Cenozoic 

geothermal gradient. 

DO TECTONICS INFLUENCE COLOR ALTERATION 

OR CARBONIZATION? 

Several regional coal-rank studies have shown 

that depth of burial and not amount of deformation is the main influence on carbonization or coalification. In many terranes containing coal-bearing 

sequences, the highest rank of coalification is usually reached during the period of greatest depth of 

burial, which may be pre-orogenic. Tectonism appears to influence coalification only where it has 

increased depth of burial. Patteisky and others 

(1962) reported that in the Ruhr basin of western 

Germany, the lowest rank of one particular coal seam 

occurs where folding and thrusting are most prominent, but where burial of the seam was minimal. 

Hacquebard and Donaldson (1974), similarly reported the preservation of pre-orogenic coalification 

patterns in Jurassic and Cretaceous coal-bearing 

strata in the Rocky Mountains and inner foothills 

belt of Canada, because rank increases uniformly 

with depth of burial, irrespective of geologic age or 

amount of deformation. Dam berger, in his 197 4 

study of coalification patterns of Pennsylvanian 

coal basins in eastern United States reported that 

coal rank in most of the basins was determined during the main phase of coalification, that is during 

the Pennsylvanian and Permian, and thus reflects 

former greatest depths of burial. 

Our laboratory experiments show that confined 

pressure in conjunction with time and temperature 

neither retards nor accelerates carbonization. 

The effects of overburden as well as tectonism on 

conodont color can be readily assessed in the northeastern part of the Appalachian basin. Figure 10 

shows a selection of localities for Early and early 

Middle Devonian conodonts in New York and Pennsylvania. The value at each locality is the total thickness of known overburden with no attempt to account for missing section. In western New York, 

overburden is relatively thin ( 4,000 ft; 1,220 m) 

and conodonts are only slightly altered (CAl 1.5-2) 

Devonian rocks are virtually flat lying across New 

York. Only the easternmost part of the outcrop belt 
107 

1Q6 

(j) 

EVALUATION OF EXPERIMENTAL DATA 

Middle Ordovician conodonts 

from Highland County, Va. 

11 

0::: 

<( 

LIJ 

>-

THICKNESS OF 

SEDIMENTARY OVERBURDEN 

z 

w 

~ 

t= 

104 

10 3 

10 2 

Pennsylvanian 1000' + 

Mississippian 3000' 

Devonian 6000' 

Silurian 1500' 

Upper Ordovician 2800' 

14,300' 

10 

CAl=l 

Temperature based on 

sedimentary burial only 

(assuming 1 °C/ 100 ft. 

geothermal gradient) 

160°C minimum 

1000 

100 

10 

Maximum 

50 100 150 180 200 230 250 300 350 400 450 500 600 

190 220 550 

RECIPROCAL OF ABSOLUTE TEMPERATURE, CALIBRATED IN oc 

FIGURE 9.-Ahrrenius plot of data from conodont open-air heating runs (same plot as in fig. 3) showing best color fit for 

Middle Ordovician conodonts from the Valley and Ridge province near Monterey, Va. The CAl of these conodonts was 

determined by comparing them with index standards. Use of this plot for determination of minimum and maximum temperature ranges of conodont samples is explained in the text. 

is within the folded and faulted Valley and Ridge 

province, which begins just west of Albany (fig. 10, 

red line). Conodont color, however, gradually 

darkens across New York and no abrupt color 

change occurs east or west of the tectonic front. 

(See fig. 16.) The color alteration in New York 

conforms chiefly to the eastward-thickening wedge 

of Upper Devonian clastic rocks. (See Oliver and 

others, 1971, sheet 6.) Conodonts in south-central 

Pennsylvania in the western part of the folded and 

faulted Valley and Ridge province are the same 

color as conodonts in flat-lying rocks, but with comparable overburden, in east-central New York. The 

darkest conodonts are in outliers east of the main 

outcrop belts and adjacent to the anthracite fields 

in eastern Pennsylvania, where Mississippian and 

Pennsylvanian rocks are thickest. Thus, it seems 

likely that tectonics do not affect color alteration 

in conodonts, but that depth of burial and the attendant increase in temperature is the dominant 

factor in observed conodont color· alteration or carbonization. 

en 

0::: 

:::J 

0 

J: 

z 

a.J 

:?! 

t= 
12 CONODONT COLOR ALTERATION 

I 0 20 40 MILES 

1-l ..,..-~+•'-;...--,,.......1' 

50 KILOMETRES I 

~-----------_;' 

0 

\/ 

\ 

Generalized outcrop area of Devonian 

rocks (from Oliver and others, 1971) 

Early or Middle Devonian • conodont locality, 

showing approximate total thickness of 

known overburden and CAl 

~---------------- -------

Western limit of 

Appalachian folding 

FIGURE 10.-Map showing selected localities for Early and early Middle Devonian conodonts in the northeastern part of the 

Appalachian basin. Conodonts, CAl, and known overburden are shown for each locality. Note the correlation of conodont 

color (CAl) with thickness of overburden regardless of tectonic setting (compare south-central Pennsylvania with central 

New York). The thicker the overburden, the darker the conodont! 

CORRELATION OF CONODONT CAl WITH 

OTHER ORGANIC MATURITY INDEXES 

All our field collections of conodonts are from the 

Appalachian basin. At the beginning of our study, 

we had hoped to tie conodont color alteration to 

percent fixed carbon via the isocarb (or isorank) 

maps for Carboniferous coals that are available for 

most of the Appalachian basin (Damberger, 1974, 

figs. 6, 7, and map references cited on p. 71). These 

maps are based on bulk chemical analysis of coals 
CORRELATION WITH OTHER ORGANIC MATURITY INDEXES 13 

or on vitrinite reflectance. Unfortunately, conodonts 

were absent from the few marine carbonate rocks 

interbedded with the higher rank coals of the eastern half of the northern Appalachian basin. Thus, 

it was necessary to correlate conodont CAl with 

percent fixed carbon using chemical analysis of the 

conodont host rock or another organic maturity index. 

Amoco Production Company kindly analyzed 66 

of our conodont-bearing limestones from throughout Appalachian basin for weight percent fixed carbon in kerogen. Surprisingly, there was not enough 

kerogen in any of the 66 500-gram samples to make 

this determination. The clean marine carbonate 

rocks in which conodonts are abundant are disappointingly low in kerogen. Fortunately the conodontbearing samples also contained palynomorphs and 

vitrinite which could be tied to previous chemically 

determined fixed-carbon standards. Palynomorph 

translucency (Gutjahr, 1966; Staplin, 1969; Correia, 1971) and vitrinite reflectance measurements 

(Bostick, 1970; Castano and Sparks, 197 4; Hacquebard and Donaldson, 1970; Patteisky and others, 

1962; Teichmtiller and Teichmtiller, 1968) were made 

using the same rock samples from which conodont 

CAl had been determined. Figure 11 shows the correlation of these three indexes. The columns under 

conodonts give CAl and temperature ranges derived from the Ahrl"enius plot of the experimental 

data. The columns for palynomorphs give the translucency carbonization indexes used by Amoco Production Company. The values are visual estimates 

made using transmitted-light comparison of an unknown to a specific palynomorph translucency standard. Amoco has equated their translucency indexes 

to weight percent fixed carbon in kerogen and these 

values are also shown here. The palynomorph correlation is based on 66 limestone samples of Ordovician through Mississippian age from the Appalachian basin. Seven percent of the samples (not ineluded in the 66) originally submitted for processing 

had no palynomorphs; these were mainly samples 

of deep-water limestone. 

Conodont color alteration does not begin until a 

late stage of palynomorph diagenesis (fig. 11). Thus, 

CAl 1 equals translucency indexes 1 through 5. 

Palynomorphs, therefore, and not conodonts, are excellent indicators of low-temperature organic metamorphism. They have been successfully used in the 

petroleum industry as low-level organic maturity 

indexes, especially in the critical realm of threshold 

hydrocarbon generation ( Gutj ahr, 1966; Staplin, 

1969; Correia, 1971; Staplin and others, in press). 

Conversely, palynomorphs are cruder indexes of 

late-stage organic metamorphism than conodonts 

(fig. 11). Moreover, vitrinite reflectance measurements on many of the same samples used to correlate conodont CAl and palynomorph translucency, 

corroborate the greater accuracy of conodont CAl at 

these high levels of organic metamorphism. 

Palynomorph and conodont indexes dovetail 

nicely; palynomorphs provide an accurate assessment 

of early-stage organic metamorphism and are best 

preserved and most abundant in clastic rocks; conodonts provide a better assessment of late-stage organic metamorphism and are most easily obtained 

from carbonate rocks. 

The vitrinite correlation (fig. 11) is based on 20 

limestone samples of Devonian and Mississippian 

age from the Appalachian basin. Many more samples were processed for vitrinite; unfortunately, 42 

percent of all samples processed had none. Vitrinite 

is least abundant in the relatively clean marine carbonates in which conodonts are most abundant. Because so many of the conodont samples lacked vitrinite, we tried to obtain reflectance readings on the 

very fine dispersed organic matter within the conodont element itself. The mineralogy of the conodont 

interfered with and made reflectance readings on 

CONODONTS PALYNOMORPHS VITRINITE 

TEMEPERATURE TRANSLUCENCY 

CAl "C INDEX (AMOCO) 

1 <50-80 1-5 

1Y2 S.0-90 5-up. 5 

2 60-140 5-6 

3 110-200 up. 5-6 

4 190-300 6 

5 300-400 up.6-7 

FIGURE 11.-Chart showing correlation of three organic metamorphism indexes; all are optical techniques. Palynomorph 

translucency and vitrinite reflectance determinations were 

made on the same rock samples from which conodont CAI 

had been determined. The temperature ranges for conodonts 

are from the Ahrrenius plot of the experimental data and 

WEIGHT PERCENT PERCENT 

CARBON IN FIXED 

KEROGEN REFLECTANCE CARBON 

<82 <0.8 <60 

81-84 0.7-0.85 60-65 

81-87 0.85-1.3 65-73 

83-89 1.4-1.95 . 74-84 

84-90 1.95-3.6 84-95 

+90 +3.6 +95 

represent heating durations of 500 million to 1 million years 

(lower temperature is 500 m.y.-value). The upper temperature limit for CAI 5 is from experiments now in progress. 

The translucency indexes are me,an range values and are 

visual comparison estimates and not photometric determinations. 
14 CONODONT COLOR ALTERATION 

the organic matter impossible. Vitrinite reflectance 

determinations were also used to check areas where 

conodont CAl appeared to be geologically anomalous. In all cases, the vitrinite data corroborated the 

CAl values (see fig. 16, area of high CAl and correspondingly high reflectance in Maryland and West 

Virginia). According to most investigators, (for example, Hacquebard and Donaldson, 1970 ; Bostick, 

1974), vitrinite reflectance measurements are best at 

high levels of organic metamorphism-above 62 percent fixed carbon. Vitrinite is generally confined to 

Devonian through Quaternary deposits and is most 

abundant in fine-grained clastic rocks ; conodonts, on 

the other hand, are found in marine, chiefly carbonate and to a lesser extent, clastic rocks of Cambrian through Triassic age. 

The three optical indexes of organic maturity can 

be compared for age and thermal range, and ease 

and expense of laboratory preparation and index 

determination (fig. 12) . The age and thermal ranges 

of the three indexes combine well to cover most 

geologic conditions. Conodonts overlap and extend 

below the age range of vitrinite, providing a good 

index of maturity for Ordovician and Silurian 

rocks, and to a lesser extent, of Cambrian rocks 

where conodonts are rare. 

Palynomorphs are longer ranging than either 

conodonts or vitrinite (fig. 12). Palynomorphs can 

be used to assess organic metamorphism lin terranes 

where maximum temperatures were n~ver higher 

than 50° C or where fixed carbon values are less 

than 60 percent. Many spores and pollen do not survive in terranes where fixed carbon is greater than 

70 percent (Wilson, 1961). Vitrinite can be read 

to 100 percent fixed carbon equivalence or even to 

graphite-grade metamorphic facies (Schapiro and 

Gray, 1966). According to Bostick (1974), vitrinite 

reflectance measurements are most appli~able above 

80° C. Conodonts extend into garnet-grade metamorphic facies where rocks have beenl regionally 

subjected to temperatures as high as 500° C. Conodont CAl cannot discriminate temperature intervals below 50° C. 

Who can make conodont CAl determinations? In 

contrast to palynomorph and vitrinite indexing 

which require a trained operator with technical 

skills (determinations are generally made by a 

palynologist or coal petrologist), conodont indexing can be accomplished by anyone who isn't color 

blind. The cost of conodont preparation and indexing is relatively small. Preparation of carbonate 

samples requires acetic- or formic-acid demineralization followed by heavy-liquid separation using 

bromoform or tetrabromethane, and then color determination with a standard binocular microscope. 

Palynomorph translucency indexing requires a more 

chemically complicated concentration procedure, followed by either a rapid and inexpensive visual comparison using translucency standards for index determination, or by a more expensive photometric 

determination. (See Gutjahr, 1966, for a description 

of laboratory processing and photometric determination.) Commercial laboratories price organic-maturity assessment using palynomorph translucency 

techniques at $30-$50 per sample· ( 1975). 

Vitrinite analysis involves concentration techniques similar to those for palynomorphs but requires a more careful and complicated mounting 

procedure, as well as more sophisticated and expensive optical hardware. Vitrinite reflectance determinations are made by some major oil companies 

and a few state and federal coal laboratories. Commercial laboratories charge $40-$180 per sample 

for reflectance determination ( 1975). 

EFFECTS OF HOST ROCK ON ORGANIC 

METAMORPHISM 

We had initially intended to correlate conodont 

CAl in Pennsylvanian carbonate rocks to existing 

fixed-carbon determinations (chemical and optical) 

in nearby or interbedded coals. This correlation was 

not possible. We did, howeve,r, plot the vitrinite 

fixed-carbon values obtained from our Devonian and 

Mississippian carbonate rocks on Pennsylvanian 

coal ioscarb maps (Ashley, 1928; Damberger, 1974; 

Eby, 1923; Meyer and Edgerton, 1968; Postley, 

AGE RANGE __________________ __!_______ c~:=~~AO:~~ PALYNOMORPHS VITRINITE 

PRECAMBRIAN DEVONIAN 

TRIASSIC. TO HOLOCENE. TO HOLOCENE. 

TEMPERATURE RANGE --------------- 50°-500° C 

OPERATOR ---------------------1------- Almost anyone EXPENSE ----------------- ----- ------- $1Q-$25 per sample 

<160° C >Sooc• Palynologist Palynologist 

$3Q-$50 per sample $40- $180 per sample 

*Schapiro and Gray (1966) have used vitrinite reflectance measurements to separate different stages of natural coke and graphite at rj:!ftectances as high as 11.5. These values represent temperatures com- parable to the upper temperature limit of conodonts. 

FIGURE 12.-Chart comparing age and thermal range and relativ,e cost of three organic 

maturity indexes; all are optical techniques. 
EFFECTS OF HOST ROCK 15 

1935). Vitrinite fixed-carbon values from the carbonate rocks averaged 7 percent fixed-carbon points 

lower than fixed-carbon values of Pennsylvanian 

coals in the same area. This was surprising, especially as the limestones were 1,000 (305 m) to 7,000 

(2,135 m) feet stratigraphically below the Pennsylvanian coals. The literature on vitrinite reflectance indicates some controversy concerning the influence of host-rock lithology on reflectance. Some 

workers have found that vitrinite scattered in country rocks often has the same or only slightly different reflectance values than vitrinite in adjacent 

coal beds (Ammosov, 1970). Castano and Sparks 

(1974) found virtually no difference in vitrinite reflectance of coal-shale pairs, provided that vitrinite 

was relatively abundant in the shale, or the sample 

size was sufficiently large. Where sample size or 

amount of vitrinite was small, a marked difference 

in reflectance values of coal- and shale-derived vitrinite was noted. They attributed this difference to 

the disproportionate influence of recycled and 

weathered vitrinite in small samples or to samples 

having a low amount of indigenous vitrinite. Several 

major oil companies have informed us that within 

an interbedded sequence of coals, sandstones, shales, 

and limestones, fixed carbon determined from vitrinite reflectance can vary by as much as 5-10 percent between lithic types; the coals have the highest 

values and the carbonate rocks the lowest values. If 

this variation were solely a function of greater vitrinite abundance in rocks other than carbonate rocks, 

as suggested by Castano and Sparks (1974), then 

the carbonate rocks, which generally have the least 

vitrinite, would yield the highest reflectance values 

because of their higher content of reworked and 

weathered vitrinite. Our own plots of carbonate and 

coal data as well as oil company data show the 

carbonates to have the lowest reflectance values. 

Correia's ( 1971) study of color alteration of palynomorphs from well samples in the Paris basin, 

shows that palynomorphs having the same burial 

history are less altered in carbonate rocks than in 

mudrocks, but that palynomorphs extracted from 

carbonate rocks have more uniform alteration patterns than palynomorphs from mudrocks. According to Timofeev and Bogolyubova (1963) and Chichua (1964), the reflectance and refractiv index of 

vitrinite differ sharply from sandstones nd mudstones; the mudstones have the highest val es. Vitrinite reflectance may be affected by the per eability, 

porosity, and chemical composition, all of which 

affect thermal conductivity, of the host 

mosov ( 1970) briefly discusses the effects 

conductivity on reflectance and presents a table of 

thermal conductivity coefficients for some of the 

common minerals, rocks, liquids, and gases. 

Even coal beds show variation in reflectance. 

Vitrinite reflectance and thus percent fixed cabon 

are known to increase regularly from the center of 

a coal bed to its upper and lower contacts (Ammosov, 1970). Wilson (1961) reported this phenomenon as a common occurrence in the Arkoma basin 

of Oklahoma and Arkansas. 

Because of the unknown effects of host-rock texture and composition on organic metamorphism, it 

seemed preferable to tie conodont CAl to percent 

fixed carbon determined from vitrinite derived from 

the same host rock and to limit our study to one 

reasonably homogeneous rock type-limestone. 

FIELD EVALUATION AND APPLICATION OF 

CONODONT CAl 

The Appalachian basin is an ideal area to field 

test the CAl of conodonts because most of the bedrock is of Paleozoic age. Igneous and metamorphic 

rocks of the Adirondacks (New York), Blue Ridge, 

and Piedmont terranes outline the basin on the 

north and east. Coastal Plain deposits overlap the 

basin on the south (in Alabama and Georgia) and 

the Nashville dome, Jessamine dome, and Cincinnati 

arch bound it on the west (fig. 13). 

Alteration index maps were compiled for the Appalachian basin using our own collections and many 

specimens and samples kindly loaned to us by colleagues in universities, state surveys, and the petroleum industry. Almost all collections are from limestone; 66 of our 705 samples are from the subsurface. Conodonts from noncarbonate rocks were not 

used, so that variation in host-rock lithology could 

be neglected. To be sure, conodonts from other rock 

types also change color. Many bedding planes of 

black shale and siltstone from the U per Devonian 

and Lower Mississippian Chattanooga Shale from 

the west half of the .southern Appalachian basin contain conodonts, Sporangites (a megascopic palynomorph), and phosphatic brachiopods. All three organic elements are darker in slabs from more easterly outcrops, where overburden was greater in the 

Appalachian basin. 

Because depth and duration of burial affect color 

alteration, we compiled conodont CAl isograd maps 

for three stratigraphic intervals: Ordovician, Silurian through Middle Devonian, and Upper Devonian 

through Pennsylvanian. These intervals were chosen 

mainly because they contain widespread marine carbonate rocks. 
16 CONODONT COLOR ALTERATION 

ORDOVICIAN CAl ISOGRAD MAP 

Figure 13 shows CAl isograds for mainly Middle 

Ordovician conodonts in the Appalachian basin. 

Analysis of the isograd map requires an isopach map 

of Middle Ordovician through Permian rocks. Such 

82° 

a map was compiled for the basin (not shown in 

this report) using data given in de Witt (1975), de 

Witt, Perry, and Wallace (1975), and Miller (1975). 

Throughout most of the basin, CAl isograd and isopach trends are conformable, especially in the west-

/ / 

1.5 •• 

I 

/ / 

44·-i--1 

./ 

I 

IND. 

O\ 

go• 

' / 

( 

EXPLANATION 

0 

Surface sample Drill-hole sample 

34·--+- Conodont locality 

®2 

Anomalous CAl value 

I 

I 

I 

0 

0 

100 MILES 

100 KILOMETRES 

----2 

CAl isograd-drawn on first occurrence of 

index value, dashed where inferred . 

Based on 366 surface and 31 drill-hole 

localities. 

FIGURE 13.-Map showing CAl isograds in Ordovician rocks in the Appalachian basin. Conodonts from 60 Lower Ordovician, 

308 Middle Ordovician, and 29 Upper Ordovician localities were indexed, for a total of 397 points. Wherever possible, 

early Middle Ordovician collections were used in order to provide as uniform a stratigraphic position as possjble. 
FIELD EVALUATION AND APPLICATION 17 

ern and central parts of the basin where Ordovician 

rocks are mainly in the subsurface and deformation 

is minimum. The consistent westward bulge of Ordovician isograds in Pennsylvania reflects the con1posite effect of eastward-thickening Silurian, Devonian, Mississippian, Pennsylvanian, and Permian 

clastic wedges that are superimposed in that area. 

In most of Pennsylvania the original post-Ordovician overburden patterns are not as severely disrupted by late Paleozoic faulting as in areas south 

of central Virginia. 

In western Pennsylvania, Ohio, West Virginia, 

and Kentucky, areas where most of the post-Ordovician rock sequence is still preserved, a comparison 

of Ordovician CAI isograds and Middle Ordovician 

to Permian isopachs show that: ( 1) conodont color 

alteration ( CAI=l.5) begins at about 4,000 feet 

(1,220 m) of overburden; (2) CAI 1.5 persists 

from 4,000-8,000 feet (1,220-2,440 m) of overburden; (3) CAI 2 persists from about 8,000-12,000 

feet (2,440-3,660 m) of overburden; ( 4) CAI 3 

persists from about 12,000-18,000 feet (3,660-5,490 

m) of overburden; ( 5) CAI 4 persists from about 

18,000-25,000 feet (5,490-7,625 m) of overburden; 

( 6) CAI 5 begins at about 25,000 to 30,000 feet 

(7,625-9,150 m) of overburden. If the paleogeothermal gradient is assumed to have been similar 

to the present-day average geothermal gradient ( 1 o 

C per 100 ft) and to have been reasonably consistent 

throughout post-Ordovician time, then from the 

above data, the CAI 11 -2 interval ( 4,000-8,000 

ft overburden interval) equates to a temperature 

range of 60 °-100° C. The experimental data (figs. 

3, 5) predict a 50°-90° C range for the field of CAI 

1 Vt to 2. CAI 5 begins at about 25,000 to 30,000 feet 

of overburden (or at a calculated temperature of 

270°-320° C). The experimental data indicat e 300° 

C for the threshold of CAI 5. The close correlation 

of these temperature ranges indicates an apparent 

long-lived and consistent average geothermal gradient for a large part of the Appalachian basin. 

Moreover, the close correlation of these data also 

indicates that in the Appalachian basin, CAl values 

can be used to estimate overburden values, restore 

missing section, and reconstruct basin configuration. 

An overview of figure 13 shows CAI 1 in areas 

having minimal burial history, which are along the 

western edge of the basin following the Nashville 

dome, Jessamine dome, and Cincinnati arch. Overburden and CAl increase eastward. Isograd trends 

and the strike of .the overriding Blue Ridge-Piedmont terrane are discordant in Alabama, Georgia, 

Tennessee, and southern Virginia. In Georgia and 

Tennessee, isograds parallel trends of major fold 

axes; both fold axes and isograds strike into the 

overthrust Blue Ridge-Piedmont terrane, indicating 

metamorphism preceeded thrusting. Thus we see 

preservation of prethrust carbonization patterns. 

The circled localities (fig. 13) are anomalously 

low CAI values within higher index terrane. In 

Tennessee, conodonts from a window in the Great . 

Smoky thrust sheet have a CAI of only 2. The two 

localities in New Jersey are in Taconic-type klippen 

whose present structural positions must therefore 

be the result of Appalachian thrusting. The anomalous areas have had a cooler thermal history than 

the surrounding terranes. These areas have farreaching paleogeographic and tectonic implications. 

In Tennessee and New Jersey, the conodonts are 

from rbcks representing the eastern edge of the 

Appalachian basin, which were thrust westward 

during a late tectonic event and are now near the 

depocenter of the basin. 

The CAl 3 high in cental northeast Alabama, may 

reflect an area of high heat flow, because it does not 

correlate with either isopach or structural trends. 

The westward bulge of the CAI 4 isograd in Highland County, Va., does correlate with an area of 

Cenozoic igneous activity. 

Figure 14 shows the Virginia-West Virginia 

border area that includes the area of Cenozoic 

igneous activity. CAl isograds for Ordovician and 

Upper Silurian-Lower Devonian rocks have been 

superimposed on maximum isotherms for hot 

springs. The western bulge of the isograds on both 

maps can be explained by a higher than average 

heat flow associated with the known Eocene intrusions. Known overburden alone does not account for 

the high CAI values. Ideally, one would expect to 

see better closure of isograds around intrusions. The 

data points, however, were inadequate for more detailed contouring. The Ordovician CAl highs in the 

southern part of the map area showed no correlation with either isopach data or known igneous activity. The central West Virginia-Virginia border 

area, however, has long been known for its spas 

and thermal springs, and towns named Hot Springs, 

Warm Springs, and Mineral Springs dot the area. 

The hot spring isotherms show a high coincidence 

with Ordovician CAl highs. Thus, the isotherm configuration and the CAl highs may be related to a 

buried pluton from which the waters in the area 

derive their heat. Dennison and Johnson (1971) 

earlier proposed a buried felsic pluton to account 

for the hot spring activity, small Cenozoic igneous 
18 CONODONT COLOR ALTERATION 

3 

0 50 MILES 

0 50 KILOMETRES 

FIGURE 14.-Maps of the West Virginia-Virginia borde'I' area showing Ordovician and Upper Silurian to Lower Devonian 

CAl isograds (solid lines) superimposed on maximum isotherms, in degrees Fahrenheit, for hot springs (dashed lines). 

Isotherms from Dennison and Johnson (1971). 

intrusive rocks, and large· negative gravity anomaly 

in the Virginia-West Virginia border area. 

Figure 15 shows the major faults in the Valley 

and Ridge province of Tennessee and a few localities for Middle and Late Ordovician conodonts. The 

lightest conodonts are from the Nashville dome area 

to the west. CAl 1 persists into the Pine Mountain 

overthrust block and then conodonts become progressively darker through more easterly thrust 

belts-from the Sequatchie to the Dumplin Valley. 

Conodonts from the Tuckaleechee Cove window in 

the Great Smoky thrust sheet, however, have a CAl 

of only 2, indicating that these rocks could not have 

been buried as deeply or have reached the same degree of thermal maturity as correlative rocks, 10-

15 miles ( 16-24 km) to the west, which are exactly 

the same age but have conodonts with a CAl of 4 

(fig. 15). 

SILURIAN THROUGH MIDDLE DEVONIAN CAl 

ISOGRAD MAP 

Almost all points shown on the map (fig. 16) are 

for uppermost Silurian and lowermost Devonian 

limestones. Early Devonian conodonts near the Allegheny front in Pennsylvania have CAl values of 

2.5 to 3. The 4 index first occurs 30 miles ( 48 km) 

across strike to the east. The 4 isograd on this map 

is considerably east of the 4 isograd on the Ordovician map (compare figs. 13 and 16). Along the 

eastern edge of the Valley and Ridge province in 

Pennsylvania, Early Devonian conodonts have CAl 

values of 4.5. Vitrinite particles from the same rocks 

have reflectance values of + 3.5, indicating greater 

than 95 percent fixed carbon (fig. 16, values adjacent 

to dots). Pennsylvanian coals immediately to the 

west, have 91-96 percent fixed carbon (Wood and 

others, 1969). An area of high CAl 4 occurs in 

West Virginia and Maryland. Fixed carbon values 

of 88-90 within the high, determined using vitrinite 

from the same samples as the conodonts, corroborate 

this high level of organic metamorphism. 

UPPER DEVONIAN THROUGH MISSISSIPPIAN CAl 

ISOGRAD MAP 

Figure 17 shows Upper Devonian through Mississippian localities and isograds. Pennsylvanian 
• 

Collected 

100 miles 

to west 

• 

Major thrust fault 

Sawtee.':h on upper plate 

1 

~ 

FIELD EVALUATION AND APPLICATION 

TENNESSEE 

EXPLANATION 

Cross fault 

D 

Area underlain chiefly 

by Precambrian rocks 

19 

KENTUCKY /-~-~JRGINIA __ ------- c 

0 10 20 ao 40 50 KILOMETRES 

Middle Ordovician conodont locality 

Value is color alteration index 

FIGURE 15.-Map showing major thrust faults and some localities for Middle and Late Ordovician conodonts from eastern 

Tennessee. 
20 CONODONT COLOR ALTERATION 

IND. 

goo 

0 100 MILES 

0 100 KILOMETRES 

FIGURE 16.-Map showing CAl isograds for Silurian through 

Middle Devonian rocks in the Appalachian basin. Conodonts from 43 Silurian and 108 Lower and Middle Devonian 

localities were inQexed for a total of 151 points. Isograds 

do not extend south of southern Virginia because carbonate 

rocks of this age are generally absent in the outcrop belt. 

A Devonian through Permian isopach map was compiled 

for the Appalachian basin (not shown is this report) using data from de Witt (1975) and de Witt, Perry, and 

Wallace (1975). Silurian to Middle Devonian CAl isograds 

82° 

44° ·-·+·-

EXPLANATION 

0 

Surface sample Drill-hole sample 

Conodont locality 

.as 

Conodont locality showing percent fixed 

carbon determined from vitrinite obtained from same sample as conodonts 

-----4 

CAl isograd-drawn on first occurrence of 

index value, dashed where inferred. 

Based on 144 surface and 7 drill-hole 

localities 

and Devonian to P·ermian isopachs show good correlation. 

The westward extension of all isograds in Pennsylvania 

correspond to west-trending, eastward-thickening Upper . 

Devonian, Mississippian, and Pennsylvanian clastic wedges. 

Comparison of isopachs and isograds in the north-central 

part of the Appalachian basin show that CAl 2 persists 

from 6,000 to 12,000 feet (1,830-3,660 m) of overburden 

and CAl 4 persists from about 22,000 to +26,000 feet 

(6,710-7,930 m). 
FIELD EVALUATION AND APPLICATION 21 

go· 

34·--L 

I 

0 

0 

82° 

100 MILES 

100 KILOMETRES 

EXPLANATION 

0 

Surface sample Drill-hole sample 

Upper Devonian and Mississippian 

Conodont locality 

.68 

• 

Surface sample 

Pennsylvanian 

Conodont locality showing percent fixed 

carbon determined from vitrinite obtained from same sample as conodonts 

-----2 

CAl isograd-drawn on first occurrence of 

index value, dashed where inferred. 

Based on 129 surface and 28 drill-hole 

localities 

Eastern limit of oil fields 

in Appalachian basin 

Eastern limit of dry gas fields 

in Appalachian basin 

FIGURE 17.-Map showing CAl isograds for Upper Devonian through Mississippian rocks and the eastern limit of oil and 

gas fields in the Appalachian basin (from Vlissides and Quirin, 1964). Pennsylvanian localities are shown but have not 

been contoured. Conodonts from 143 Upper Devonian through Mississippian and 14 Pennsylvanian localities were indexed. 

localities are shown separately. Mississippian conodonts along the Allegheny front in the north half 

of the basin generally have indexes of 2.5 to 3, 

whereas in the same area, Ordovician conodonts 

have an index of 4, showing increase in index with 

increase in depth of burial. An area of higher index 

terrane extends westward into part of the Pine 

Mountain, overthrust block. In this area, where 

data are closely spaced, isograds follow the fold patterns of the outcrop belts, indicating preservation 

of pre-orogenic CAl patterns. 

Figure 18 is an enlargement of a map of part of 

the southern Appalachian basin showing CAl isograds for Upper Mississippian limestones and iso-
22 CONODONT COLOR ALTERATION 

• 

_I 

I 

r'\,) '-t) ..... • 

--------r{~N . ------

• 

• 

0 

,__, 

\ 

/" 

\ 

\ 

( 

) 

,.J 

50 MILES 

0 50 KILOMETRES 

EXPLANATION 

• 0 

Surface sample Drill-hole sample 

Upper Mississippian 

Conodont locality 

• 

Surface sample 

Pennsylvanian 

Generalized outcrop area of 

Pre-Pennsylvanian rocks 

- 500-

lsopachs of Pennsylvanian rocks 

Thickness in feet 

-----1% 

CAl isograd for Mississippian rocks 

Dashed where inferred 

FIGURE 18.-Map of part of the Appalachian basin showing Upper Mississippian CAl isograds superimposed on isopachs for 

Pennsylvanian rocks (from de Witt, 1975, sheet 2). 

pachs for Pennsylvanian rocks. The Pennsylvanian 

rocks probably represent most of the post-Missisippian deposits because younger deposits were very 

thin or absent. The westward projecting lobe of the 

1.5 isograd at the Kentucky-Tennessee border may 

conform to a lobe of Pennsylvanian rocks that at 

one time extended farther westward. Significantly 

the 1.5 isograd outlines an area of oil and gas production from Mississippian rocks in Tennessee and 

Kentucky (de Witt, 1975, sheet 4). The 2 isograd 

in West Virginia encompasses the 2,500-foot-thick 

outlier of Pennsylvanian rock that must have at 

one time been part of a much thicker continuous 

northwest-trending clastic wedge. The 5,000-footthick lobe of Pennsylvanian rock in southern Virginia is not noticeably reflected in the CAl isograds 

because we have no subsurface data in that area. 

The northwest-trending area of CAl 2 to 3.5 in 

southeast West Virginia coincides with anomalous 

Ordovician CAl highs (figs. 13, 14). These highs 

probably result from the high heat flow associated 

with a buried pluton. 

CAl ISOGRADS PROVIDE CUTOFFS FOR OCCURRENCE 

OF HYDROCARBONS 

CAl isograds for Ordovician rocks and the eastern limit of oil and gas fields (Vlissides and Quirin, 

1964) producing from Ordovician rocks in the Appalachian basin are shown in figure 19. The oil fields 

are west of the 2 isograd in surface rocks and gas 

production is in areas where surface rocks have CAl 

values of 2 to 3. 

lsograds for Silurian through Middle Devonian 

rocks and the eastern limit of oil and gas fields in 
FIELD EVALUATION AND APPLICATION 23 

90' 

I 

I 

I 0 100 MILES 

0 100 KILOMETRES 

EXPLANATION 

Anomalous CAl value 

----2 

CAl isograd for Ordovician rocks. Dashed 

where inferred. Based on 397 localities 

Eastern limit of oil fields 

producing from Ordovician rocks 

Eastern limit of gas fields 

producing from Ordovician rocks 

FIGURE 19.-Map showing CAl isograds for Ordovician rocks and the eastern limit of oil and gas. fields (from Vlis.sides and 

Quirin, 1964) in these same rocks in the Appalachian basin. Circled localities are areas of low CAl within higher index 

terrane. 

these same rocks are shown in figure 20. The oil 

fields are once again west of the 2 isograd in surface 

rocks, but gas production extends into areas where 

surface rocks have CAl values as high as 4. 

Figure 17 shows that an alteration index of 2: appears to be just east of the upper thermal limilt of 

known oil and condensate production. A CAl of 1.5 

correlates with a fixed carbon range of 60-65 percent and with a vitrinite reflectance range of 0.7-

0.85 (fig. 11). Most reports give 0.8 reflectance 

and 62-65 percent fixed carbon as the cutoff for 

most commercial oil and condensate production 
24 CONODONT COLOR ALTERATION 

82' 

I 44'--t90' 

34'-r 

0 100 MILES 

0 100 KILOMETRES 

EXPLANATION 

-----2 

CAl isograd for Silurian through Middle 

Devonian rocks. Dashed where inferred . Based on 151 localities 

Eastern limits of oil fields producing 

from Silurian through Middle Devonian 

rocks 

Eastern limit of gas fields producing 

from Silurian through Middle Devonian 

rocks 

FIGURE 20.-Map showing CAl isograds f or Silurian th rough Middle Devonian rocks and the eastern limit of oil and gas fields 

(from Vlissides and Quirin, 1964, and de Witt, P erry, and Wallace, 1975) in these same r ocks in the Appalachian basin. 

(Bostick and Damberger, 1971, table 1). It is important to note that cutoffs for oil production for 

different stratigraphic intervals are not coincident 

geographically. In Pennsylvania, dry gas has been 

produced from strata containing coal beds and dispersed coaly particles in an area where surface rocks 

have fixed carbon values of 90 percent or higher. 

The upper thermal limit for dry gas production appears to be near an index of 4 to 4.5. Interestingly, 

this may also be near the thermal threshold for the 

development of slaty cleavage (Epstein, 197 4). A 

CAl of 4-4.5 correlates with a fixed carbon range 
FIELD EVALUATION AND APPLICATION 25 

of 84-95 percent and a vitrinite reflectance range of 

0.95-3.6 (fig. 11). Bostick and Damberger (1971, 

table 1) show 95 percent fixed carbon and a reflectance of 3.0 as the limit for commercial dry gas production. 

The maps indicate that the best potential for oil 

or gas production is in the western part of the southern Appalachian basin and the best potential for 

gas production is in the eastern part of the southern 

Appalachian basin. 

Some possibilities for gas exist beneath the leading edge of the Blue Ridge-Piedmont terrane a s indicated by thermal lows in windows and klippen in 

that area (fig. 19). 

CONCLUSIONS 

The color alteration index (CAl) of conodonts is 

a valuable tool for assessing organic metamorphism 

because: 

1. It is a rapid and inexpensive method requiring 

only standard laboratory techniques and a 

binocular microscope. 

2. A color chart can be used for index determination or a set of standards can be assemb1ed 

from field collections or cooked in the laboratory. Thus standards can be easily assembled 

and reproduced. 

3. Conodont color alteration begins near the upper 

thermal limit for many palynomorphs. The 

CAl of conodonts provides thermal cutoffs 

for oil, condensate, and dry gas production. 

4. The CAl of conodonts is applicable to rocks as 

old as Cambrian, whereas reflectance techniques for vitrinite cannot be used for pre-Devonian rocks. 

5. AND MOST IMPORTANT-Conodonts are most 

abundant and most easily concentrated from 

marine carbonate rocks in which palynomorphs 

are generally poorly preserved and in which 

vitrinite is least abundant and often absent. 

ACKNOWLEDG~IENTS 

We wish to thank P.R. Rose, U.S. Geological Survey, for his enthusiastic support of our study and 

for seeing its potential. C. W. Cressler, U.S. Geo·-

logical Survey, was invaluable in locating all the 

outcrops of fresh Paleozoic carbonate rocks in northwest Georgia. Thanks are due the Georgia Geological Survey for field support in the largest state 

east of the Mississippi. Many colleagues in universities, state surveys, and the petroleum industry 

provided us with specimens and (or) carbonate 

samples from the Appalachian basin. They include, 

S. G. Barnett, III, SUNY, Plattsburg, N.Y.; P. J. 

Brown, Columbia Gas Transmission Corp.; J . A. 

Drahovzal, Alabama Geol. Survey; P. W. Goodwin, 

Temple Univ.; G. K. Merrill, The College of Charleston; W. C. Sweet, The Ohio State Univ.; C. G. Tillman, Virginia Polytechnic Inst.; C. C. Rust, General Crude Corp.; Shell Canada Ltd.; Amoco Production Co.; Columbia Gas Transmission Corp.; we 

hope we remembered them all. 

N.H. Bostick and H. H. Damberger, Illinois Geol. 

Survey, J. A. Clendening, Amoco Production Co., 

F. L. Staplin, Imperial Oil Ltd., and Logan Urban, 

Phillips Petroleum, were exceedingly helpful in discussing the technology and application of other organic indexes with rank amateurs. J. A. Clendening 

also provided us with the palynomorph translucency 

determinations. 

We are deeply indebted to P. J. Brown, Columbia 

Gas Transmission Corp., for providing us with numerous well samples from the central Appalachian 

basin. Special thanks are also due S. M. Bergstrom, 

The Ohio State Univ., for providing us with access 

to his numerous Appalachian basin collections and 

to the collections of the Orton Museum. We thank 

him too for the use of office space and for the conodont-rich rock samples from which we obtained all 

our experimental specimens. Charles Sandberg, U.S. 

Geological Survey, reviewed the manuscript and 

provided several helpful suggestions and criticisms. 

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i:7 U.S. GOVERNMENT PRINTING OFFICE : 1976 0-215-329