INFERENCES ABOUT THE ORIGIN OF OIL AS · INDICATED BY THE COMPOSITION OF 

THE ORGANIC CONSTITUENTS OF SEDIMENTS 

By PARKER D. TRASK 

ABSTRACT 

Petroleum originates mainly from the organic matter in 

marine sediments, which is derived chiefly from remains of 

planktonic organisms in the overlying water. The originf~-1 

organic source material, represented by ·the plankton, is taken 

in as food by many other types of organisms in· succession, 

and in this process of utilization it decreases very greatly in 

quantity before the time it reaches the sea floor and is deposited 

in the sediments. The quantity of organic material continues 

to diminish after it is buried in the sediments, but the rate of 

diminution is small compared with the rate while the organic 

matter is in the overlying water. The composition of the 

average plankton i~ 24 percent of protein, 3 percent of fat, and 

73 percent of carbohydrates and other nonnitrogenous cOinpounds. In recently deposited sediments the proportion is 

protein 40 percent, fat 1 percent, and carbohydrates and other 

compounds less than 60 percent. In ancient (lithified) sediments the proportion is protein 27 percent, fat 1 rercent, and 

other compounds more than 60 percent. 

As the organic matter passes from plankton to lithified sediments it tends to become more complex in composition. This 

is because the oxygen content decreases progressively with depth 

in the buried sediments, and in an environment deficient in 

oxygen complex organic matter becomes progressively less satisfactory as food for living organisms; thus the unutilizable 

residue becomes more and more complex. The influence of 

the lack of free oxygen in the environments in which the 

organic matter lies is refle.cted in the progressive loss of oxygen 

in the organic constituents between the time of formation of 

the plankton and the time of the burial of the organic matter 

in the sediments. In plankton the oxygen content of the 

organic constituents is estimated to be 39 percent, in recent 

sediments 30 percent, .and in ancient sediments 23 percent. 

These are average figures; individual samples may vary considerably. · 

Estimates of the ultimate composition of the organic matter 

in different stages of its history afford a means of evaluating 

the ratio of organic matter to carbon. This ratio is a useful 

index in calculating the organic content of substances provided 

the qi1antity of carbon is known. The average ratio of total 

organic matter to carbon in plankton is 2.1, in recent sediments 1.8, and in ancient sediments 1.6. 

Cellulose, fats, and simple proteins ordi:r;1arily seem to be 

present in sediments in amounts too small to be the principal 

source of petroleum. Further evidence against fats as a source 

of oil is the unsaturated character of the fats compared with the 

saturated character of petroleum; the prevalence of naphthene 

and other ring compounds ·in crude oil and their scarcity in 

fats; and the chemical stability of fatty substances. Petroleum 

apparently must come mainly from other compounds, such as 

complex proteins and nonnitrogenous complexes. 

The tendency of the organic constituents to come to chemical 

equilibrium after they have been buried to .a depth at which 

bacterial decomposition is insignificant is regarded as a possible 

79196-37 

factor in the · generation of liquid hydrocarbons. Liquid hydrocarbons after they are formed may dissolve organic substances. 

The organic constituents of the resulting solution may then 

react with one another in an effort to reach a point of equilibril.Jm. 

Repeated solution and subsequent adjustments of this character 

lead eventually to the formation of petroleum. · 

INTRODUCTION 

To solve the problem of the origin of petroleum it 

is essential to know something about the composition 

of the substances from which the oil might be derived. 

Much information concerning source beds has been 

gathered in the course of studies supported jointly by 

the United States Geological Survey and the American 

Petroleum Institute. The av~ilable data suggest certain inferences about the origin of oil, which are presented in this paper for consideration by geologists. 

Petroleum is generally believed to be formed from 

organic substances that have accumulated in sediments. The geologic conditions under which it is 

found indicate that it is commonly derived from finegrained marine deposits, though some oil possibly niay 

have originated from continental sediments. The 

mother materials of petroleum, therefore, being large.ly 

confined to marine sediments, must be derived irom 

organic matter present in the overlying water. Most 

of this organic matter originates in the sea water itself, 

but some is washed from the land. . 

The successive changes in the chemical nature of 

the mother substances of petroleum from the time 

these substances first g~t into the water until they 

accumulate in the underlying sediments give clues as 

to the processes that may take place after they have 

been deposited. After sediments have been buried to 

a depth of a few feet they cannot be collected for study 

by ordinary coring devices, and the changes that take 

place in them have to be ascertained largely by in- · 

ference and by comparison with lithified sediments of 

different geologic ages which appear to have had a 

similar origin. Petroleum, apparently, is not generated 

until the sediments have been buried for some time. 1 

Consequently, any method of study that affords evidence of ways in which organic substances in sediments 

may be altered is an aid in the solution of the problem. 

I Trask, P. D., and Wu, c. c .,_Does petroleum form in sediments at time Gf deposition?: Am. Assoc. Petroleum Geologists Bull., vol. 14, pp. 1451-1463, 1930. 

147 
148 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936 

The chemical composition of. organic substances in less than 20 percent of the food they consume is transsea water and in the underlying sediments. is difficult formed into protoplasm. Consequently, even in the 

to ascertain, because of the paucity and inadequacy of type of organism that has a relatively long growing 

available information. The data, therefore, have to period, proba't>ly _a co~parativcly small proportion of 

be pres!3nted in very general form, and care must be the food consumed is transformed into protoplasm. 

taken in drawing conclusions. The inferences presented Thus -the first time the planktonic organisms serve as 

in this paper may serve mainly to stimulate discussion . f()od, a relatively large part-under ordinary conditions 

and to suggest lines of study that may advantageo~;iy much ~ore than half-is transformed into energy and is 

be pursued further. · · · lost as organic matter; a small part is excreted as unasDECR. EASE IN QUANTITY 0 ·. ~- -- ---similable residue; and only the part that goes into the 

F SOURCE MATERIAL WITH b ild' · . - · TIME u Ing of protoplasm remains as organiC matter more 

DECREASE IN WATER 

The main source of organic matter in sediments is 

the floating . plant life -the phytoplankton. 2 The 

phytoplankton serves as the main supply of food for 

the animal life of the sea, and much of it is devoured 

or decomposed before it is buried in the underlying 

sediments. . ·· 

When organic matter in any form is taken in as food 

by another organism, part of it is assimilated into the · 

tissues of the organism, part is excreted as unutilizable 

residue, and the rest is used by the organism to generate 

energy. The part that is converted into energy is 

largely destroyed in the process, leaving waste products, 

such as carbon dioxide and water. 

The quantity of unutilizable residue in food is small, 

though the proportion varies somewhat with the form 

of food and the type of animal that eats it. . In human 

beings the quantity of unassimilable residue is about 

5 percent of the food consumed,3 and this fig~e can be 

taken as generally indicative of the small proportion 

of unassimilable organic matter in the food eaten by 

other organisms, such as marine animals. 

The proportion of the food transformed into body 

tissue also is small. If the mature stage of the animal 

is long compared with the growing stage, this proportion is particularly small. The plaice a kind of ' ~ flounder, may be taken as an example of an organism 

of this type in the sea. While the plaice is growing, 

about one-sixth of the food it consumes is transformed 

into body tissue/ but after it reaches maturity it 

increases very little in weight; therefore, for its life as a 

whole the quantity of food material transformed into 

pr~toplasm is ~all. If the mature stage of the orO'an- • • 0 

Ism Is short . compared with the growing stage, the 

proportion of food converted into protoplasm might 

be thought to be 'relatively large . . However, bacteria, 

which may be taken as an example of this type of 

organism, utilize less than 20 percent of the . energy 

they eyolve.5 Accordingly it may be presumed that 

2 Trask, . P. D., Origin and environment of source sediments of petroleum, pp. 

llQ-172, Houston, Tex., Gulf Publishing Co., 1932. · 

3 Sherman, H. C., Chemistry of foorl and nutrition, p. 101, New York, Macmillan 

Co .. 1918. · ·- --.. _ 

4 Petersen, C. G. J., and Jensen, P. B., Valuation of the sea, I, Animal life of the 

sea bottom, its food and quantity: Danish Bioi. Sta. Rapt, 20, p. 66, 1911. 

5 Waksnian, S. A., Principles of soil microbiology, p. 420, Bl,\ltimore, Williams, 

Wilkins Co., 1927. 

or less similar in nature to the original food material. 

The organism that .fed upon the plankton in turn 

serves as food for some other organism; with a simihtr 

transformation of organic matter into energy, residue, 

and a relatively small amount of · new protoplasm. 

This process may be repeated several times. The 

ultimate result is an immense diminution . in volume 

of the original orgamc matter, the presence of a moder-

. ate amount of unassimilable residue, and the formation of a very small proportion of living organic matter. 

· The unassimilable residue inay still serve as food for 

certain .types of organisms, but, as pointed out by 

Krogh,6 being composed of waste products,.it is likely 

to be a relatively poor source of nourishment for most 

forms of life. As the organisms that feed upon it are 

subsequently consumed by other organisms, the resulting waste products become. progressively less satisfactory as sources of food, until ultimately the residue consists of rather complex substances that are resistant 

to decomposition. · In the later stages of its history, 

particularly after it has been buried some distance 

beneath the surface of the deposits, where micro-organisms are the main forms of life present, some of the · 

organic residue may consist of undecomposed cells of 

bacteria. 

The nature and quantity of the ultimate residual 

material depends to a considerable extent upon the 

availability of oxygen for the oxidation of the organic 

substances and the resulting production of energy. 

In the water and in the upper few inches of the sediments the supply of oxygen is ordinarily adequate to 

support considerable life. In this zone, therefore, the 

organic matter decreases greatly in quantity. In fact, 

in some areas in which the water is well aerated the 

organic matter may be almost completely destroyed 

before it reaches the sea bottom, and only very little 

residual organic material may be deposited. 

DECREASE IN SEDIMENTS 

The organic matter that accumulates in sediments 

consists maiJily of the resistant residual compounds. 

After it has been buried a few inches beneath later 

sediments, it is associated with little or no free oxygen 7 

6 Krogh, A., Dissolved substances as a food of aquatic organisms: Conseil perm. 

expl. mer Rapports et proces-verb., vol. 75, pp. 7-37, 1931. 

7 ZoBell, C. E., and Anderson, D. Q., Vertical distribution of bacteria in marine 

sediments: Am. Assoc. Petroleum Geologists Bull., vol. 20, p. 266, 1936. 
INFERENCES ABOUT THE ORIGIN OF OIL 149 

and hence is unlikely to be altered greatly during its 

future history. The remarkable decrease in number 

of bacteria within the · upper 8 inches of marine sediments 8 is evidence of the decreas~ in oxidation of 

organic matter. Thus, the rate of decrease in quantity of organic matter is much greater during the 

interval between the time itis formed by the phytoplankton and the time it is buried a few inches beneath 

the sea floor than in the subsequent stages of its history. 

The data on the organic content of recent (unconsolidated) and ancient (lithified) sediments obtained by 

the writer and his associates in general support this 

conclusion . . The average decrease in organic matter 

within the upper 12 inches of marine sediments, as 

indicated by 150 samples of sediments from many types 

of environment, is 15 percerit,9 and the range of decrease 

is from less than 1 percent to 45 percent. Twenhofel 10 

mentions a lake in Wisconsin in which the organic content of the sediments practically disappears within a 

·few feet of the surface of the deposits, but complete 

decomposition of the organic matter within a few feet 

of the surface almost certainly is not a general characteristic of marine sediments. · Of many thousand samples of. ancient sediments analyzed by the writer and 

his associates/1 practically all contain measurable 

amounts of organic matter, and the aver~;tge organic 

content is 1.5 percent of the weight. In recent marine 

sediments of similar character, represented by about 

2,000 analyses from many parts of the world, the 

average organic content is 2.5 pei'cent.U The number 

of samples is so large and the localities from which they 

came are so wjdespread that the data may be considered as indicating the general order of magnitude of 

the organic content of recent and ancient fine-grained 

• Idem, p. 262. Reuszer, H. W., Marine bacteria and their role in the cycle of life 

in the sea, Ill, The distribution of bacteria in the ooean waters and muds about Cape 

Cod: Biol. Bull., vol. 65, pp. 48G-497, 1933. 

9 Trask, P. D., op. cit., p. 206. 

. Io Twenhofel, W. H ., Sedimentation and stratigraphy from modern points of 

view: Jour. Paleontology, vol.8, pp. 456-458, 1934. 

u Trask, P. D., and Hammar, H. E., Organic content of sediments: Drilling and 

Production Practice, 1934, pp. 117-130, Am. Petroleum IIist., 1935. 

12 Trask, P. D., Origin and environment of source· sediments of petroleum, pp. 

249-284, Houston, Tex., Gulf Publishing Co., 1932. · 

marine clastic sediments. The average loss in organic · 

content during burial is therefon of the order of magnitude of 2.5-1.5, or 1 percent, and the proportionate 

.loss is 1.0-;-2.5, or 40 percent. This figure ' of 40 per~ 

cent naturally is an approximation, and the loss in 

individual sediments may differ considerably from it. 

Nevertheless, the loss of organic matter iii buried sediments is relatively small compared with the loss of 

organic matter between its planktonic source and the 

form in which it occurs in the upper layers of sediment. 

GENERAL COMPOSITION OF ORGANIC MATTER 

PLANKTON 

The phytoplankton (the part of the plankton consisting of plants) comprises two main groups of organisms-the diatoms, which have siliceous skeletons, and 

the peridineans or dinoflagellates, which consist entirely of soft parts. Other forms of plant life are 

present, but these two groups represent the types that · 

are most commonly caught in tlie nets used in oceanographic investigation. The copepods, small crustaceans that feed on the phytoplankton, ate generally 

considered a part of the plankton. · 

The composition of these three forms of ,plankton, 

as determined by Brandt/3 is summarized in table 1. 

The results are ·presented on an ash-free basis and are 

given in terms of ether extract, crude protein, and 

nonnitrogenous constituents. The ~ther extract is 

roughly equivalent to the fat content; the crude protein represents the nitrogenous constituents and is 6.25 

times the nitrogen content; the nonnitrogenous constituents represent the remainder of the organic mattei-that is, the nitrogen-free, nonfatty compounds. 

The nonnitrogenous compounds correspond principally 

to the carbohydrates. The term_ "crude fiber" refers 

to the nonnitrogenous compounds that are insoluble in 

weak acid and weak alkali; cellulose is included with 

the crude fiber. 

13 Brandt, K., Beitrage zur Kenntniss· der chemischen Zusammensetzung der 

Plankton: Wiss. Meeresuntersuchungen, neue Folge, Abt. Kiel, Band 3, pp. 43-90, 

11)98 . 

. I 
150 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936 

TABLE I.-Composition of different types of organic matter on ash-free basis 

Percent 1 Ratio 

Crude 

protein 

Ether 

.extract 

N onnitrog- Crude fiber Organic mat- Carbon to 

co~~~~~ds or cellulose ter to carbon nitrogen 

Hydrogen 

atoms to carbon 

atoms 

Marine plankton:2 

Peridineans-- ----- -------~---------------------- Diatoms ______ ________ ___ _________ ____ _____ ____ _ _ 14 

29 

1.5 85? 

8 63 

42? 2. 2 12. 3 1. 77 

0 2. 0 8. 0 2. 2? Copepods ____________________________ ____ _______ _ 3 65 8 22 0 2. 0 4. 9 1. 88 Average plankton __________________ ___ ___ .:. _______ _ 24 3 73 14? 2. 1 10. 2 1. 87 

Lake plankton:4 . . Net plankton _________ ___ _______ ________ ____ ____ _ 53 8 39 5 1. 97 6. 2 -------- Nannoplankton _____________________ __ ___________ _ 49 5 46 5 1. 98 6. 4 -------- Micro-organisms: 5 

Marine algae ________________________________ ____ _ 6 3 85 4 ---------- -------- -- ------ Soil fungL _____ __ __ _______ _____ __ _______________ _ 7- 50 1- 10 37- 82 -------- 2. 05 8-50 1. 94 Soil bacteria ___ _____ ______ ______________________ _ 40- 75 -- ------ - ------- -------- 1. 78 5± 1. 65 

Marine invertebrates:o 

Crustaceans-- ------~----- ---- ------- ---- ----- Pelecypods ________ ___ ____________ __ _____________ _ Gastropods _____ _________ ____ ___ __ ____ _____ _____ _ Echinoderms ____________ ____________ _______ _____ _ VVorms __ _____ _______ __ ____ ______ __ __________ ___ _ 

Coelenterates ______________________ __ ____________ _ 

Fishes:2 . IIerring __ _____________ _____________________ __ __ _ 

Flounder ___ ~-------------------------------- -- -- Marine plants:7 Fresh ~ostera ___ ______________ ______ ___ ______ __ _ _ 

Decaying Zostera ________ _____________ ______ ___ __ _ Decomposed Zostera _______ __________ ____________ _ 

Land plan~s:2 !lay ____ ____ ___ ______________________ ____ _______ _ 

Legumes ___ _____________________ ____ ____________ _ Rye straw ___ ___ _____________ __ _________________ _ 

Sediments:s · ' 

Recent sediments ________________________________ _ Ancient sediments _______________________________ _ Surface soils ______ ...: _____________________________ _ 

75 

72 

64 

67 

64 

78 

60 

95 

19 

6 

8 

15 

22 

4 

40 

27 

34 

6 5 

8 20 

9 25 

11 18 

13 19 

11 7 

38 0 

5 0 

-- ------ 75 

-------- 90 

-------- 88 

4 81 

3 75 

2 94 

1 47 

1 63 

1 56 

0 2. 05 4. 0 1. 70 

0 2. 19 4. 2 1. 67 

0 2. 10 4. 9 1. 67 . 

0 2. 10 4. 6 1. 76 

0 1. 89 5. 1 1. 68 

0 2. 00 4. 2 1. 66 

0 ---------- 5? --------

0 ---------- 4? --------

-------- 2. 18 11. 4 -------- -- ------ 2. 41 34. 9 -------- -------- 2. 15 25. 2 --------

29 ---------- 20± -------- 36 ---------- 12± -- ------ 54 ---------- 60± --------

1 1. 7-2. 0 8-12 1. 7? 

0 1. 4--1. 8 13-20 1. 7? 

12 1. 7-2. 0 9-14 --------

1 Where the items do not add up to 100 percent the figures given represent material recovered during the analysis. 2 Brandt, K., Beitrage zur Kenntniss der chemischeu Zusammensetzung der Plankton: Wiss. Meeresuntersuchungen, neue Folge, Abt. Kiel, Band3, pp. 55-88,1898. The figures for the averaF:e plankton represent the average composition of the plankton that is caught in nets, not the numerical average of the composition of the three 

main components of the plankton, except for the figure of 14 percent for crude fiber or cellulose, which is an average for the three main groups of plankton. 3 Does not include chitin compounds. . 1 Birge, E. A., and Juday, C., The inland lakes of Wisconsin, The plankton, I, Its quantity and chemical composition: Wisconsin Geol. and Nat. History Survey Bull. 

64, p. 196, 1922. ~ Waksman, S. A., Principles of soil microbiology, pp. 377-383, Baltimore, Williams, Wilkins Co., 1927; The role of bacteria in the cycle of the life in the sea: Sci. Monthly, vol. 38, pp. 35-47, 1934. . 6 Delff, C., Beitrage zur Kenntniss der chemischen Zusammensetzung.wirbelloser Meerestiere: Wiss. Meeresuntersuchungen, neue Folge, Abt. Kiel, Band 14, pp. 56-71, 

1912. '' 1 Jensen, P . B., St~~ies concer~ing the organic matter of the sea bottom: Danish Bioi. Sta. Rept., vol. 22, pp. 36-39, 1915. s Trask, P . D ., Ongm and environment of source sedments of petroleum, p. 200, Houston, Tex., Gulf Publishing Co., 1932. 

The average composition of the plankton is 24 percent of· protein, 3 percent of fat, and 73 percent of 

carbohydrates and similar nitrogen-free substa:uces. 

The crude fiber is given as 14 percent, but this figure . 

is based on the analysis of ~ single catch of plankton 

and can be considered only as indicating that the cellulosic compounds may be !?resent in the basic planktonic source material. . In fact, all the figures for 

the average composition of the plankton are based on 

few data and represent only a rough •approximation. 

Crude protein is· more plentiful in animal life .than 

in plant life. The copepods contain 65 percent of 

·crude protein, in contrast .with 29 percent in the diatoms and 14 percent in the . peridineans. · The diatoms and copepods each contain 8 percent of fat, the 

peridineans only 1.5 percent. The peridine~ns are 

rich in carbohy;drate, and some forms presumably contain appreciable quantities of cellulose. 

In order to illustrate the relation of the marine 

plankton to other forms of life, the composition of 

several groups of animals and plants is given in table 1. 

The animal forms are ric}J_ in protein and fat. The 

plant forms are poor in protein, rich in carbohydrate, 

and, as compared with animals, poo.r in fat. The proportion of protein, fat, and carbohydrate differs considerably in the different groups of plants and animals. 

Moreover, some types of organisms differ in composition during different periods of the year. This 

seems especially true of th~ plankton.14 . 

In the absence of data for the forms of marine plankton that pass throug4 the meshes o.f the net (~he nannoplankton), figures for orga.Qisms of this group living 

in lake water in Wisconsin are included i:n table 1.15 

u Brandt, K., op. cit., pp. 43-90. 

15 Birge, E. A., and Juday, C., The inland lakes of Wisconsin, The plankton, I, 

lts quantity and chemical composition: Wisconsin Geol. and Nat. History Survey 

Bt11l. 64, p. 196, 1922. 
INFERENCES ABOUT THE ORIGIN OF OIL 151 

In this lake water the nannoplankton is similar in 

composition to the net plankton. By analogy it 

might be assumed that in the sea· also the nannoplankton is simil-ar in composition to the net plankton. 

Thus the ave!age for plankton givep. in the table may 

he assumed to indicate roughly the general composition 

of marine plankton, which may be considered a basic 

source of petroleum. However, in interpreting the 

significance of these figures with respect to the origin 

of oi1, one should bear in mind the probability that 

different types of planktonic substances are not all 

equally good sources of oil. 

ORGANIC MATTER IN SEDIMENTS 

The composition of the organic constituents of sediments is niore difficult to determine than that of plankton, because of the admixtures of inorgani~ debris. 

The data th~t have been compiled indicate that 

recent n1arine sediments contain 40~- percent of crude 

protein, and ancient sediments 27 percent. The proportion of nitrogenous compounds in the organic 

constituents of recent sediments, therefore, is less than 

in most animals and higher than in most plants. 

Furthermore, the proportion of nitrogenous compounds 

is less in ancient. sediments than recent sediments. 

The fat content of the organic substances in sediments, as indicated by the ether extract, is 1 percent, 

. which is considerably less than in plants or animals. 

Fatty substances, however, may be present in sediments in greate~" amounts than 1 per,cent, as they may 

·occur as insoluble soaps 16-that is, they may be combined with metals, such as calcium, magnesium, or 

aluminum, and therefore insoluble in ether. One of 

the most urgent needs at present is a practicable method 

of ascertaining the amount of such metallic soaps in 

sediments. 

The nonnitrogenous constituents are present in ancient sediments in greater proporti<tn than in recent 

!Sediments, and from this it may be ·inferred that they 

are relatively more resistant to d~composition than 

nitrogenous co:n::\.pounds. . 

The cellulose :~ content of marine sediments is very 

sn1all. In recent sediments it forms;,only 1 percent of 

the total organic content, and in ancient sediments it is 

practically ~bsent. The small content of cellulose in 

recent sediments and its disappearance as the sediments 

become progressively more deeply hbried may be explained as due to the readiness with which cellulose is 

attacked by microorganisms. 

Data on the composition of soils are given for comparison in table 1. The crude protein content of soils 

is 34 percent, as compared with 40 percent for recent 

16 Trask, P. D., Result& of distillation and other studies of the organic nature 

of some modern sediments: Am. Assoc. Petroleum {Jeologists Bull., vol. 11, p. 1228, 

1927. Wells, R. 0., and Erickson, E. T., The analysis and composition of the fatty 

material produced by the decomposition of herring in sea water: Am. Ohern. Soc. 

Jour., vol. 55, pp. 338-341, 1933. 

sediments. The lower protein content of soils may be 

due to the fact that the organic constituents of soils 

are derived to a greater extent from plants, which 

contain "less protein than animals. The fat content 

of soils is approximately the same as that of sediments. 

Soils are richer in nonnitrogenous compounds than 

recen~ sediments, and they contain much more cellulose. The d;.fference in the source of the organic matter 

would account for the greater content of carbohydrates 

and cellulose. 

COMPOSITION OF ORGANIC MATTE.R ON BASIS OF 

ULTIMATE ANALYSIS 

METHODS OF DETERMINING COMPOSITION 

The segregation of organic matter into protein, fat, 

and ca~bohj_drate, though generally satisfactory for 

living matt~r, is not so satisfactory for the organic 

constituents. of sediments, which consist mainly of 

residua:! products that have resisted decomposition and 

therefore no longer may properly be called proteins or 

. carbohydrates. The organic constituents of possible 

source materials of oil may advantageously be examined 

in terms of the elements of which they are composed, 

but this proeedure, too, is accompanied by difficulties, 

because in' sediments it is impossible to segregate the 

organic constituents from the in'organic constituents. 

In the determination of the organic content of sed.iments, the total quantit._1 of orga.nic matter must be 

determined, as well as tt e proportion of different elements. The principal elements in organic substances 

are carbon, oxygen, hydrogen, and nitrogen; other elements are present but ordinarily in quantities so small 

that they can be ignored without serious disadvantage 

for the purposes of this report. On this pasis the organic content can be considered as the sum of the 

carbon, oxygen, hydrogen, and nitrogen. 

Nitrogen in sediments is found almost exclusively in 

the organic constituents and is readily determined. 

Carbon can be measured directly if the mineral carbonates are first removed with acid. .Hydrogen generally cannot · be determined directly, as there is no 

good means of separating organic from inorganic hydrogen. qxygen also cannot be determined directly, 

even in org~nic matter that contains no admixed 

mineral debris~ 

OXYGEN CONTENT 

In living organisms the oxygen content is ordinarily 

taken to be th:e remainder after all the other elements 

have been Q.etermined. On this basis, the oxygen 

content in average plankton is .39 percent, in marine 

invertebrates 34 percent, in marine worms 30 percent, 

and in bact_eria 25 percent. (See table 2.) The 

oxygen content therefore seems to decrease progressively in the forms of life that feed successively on the 

original plankton. 
152 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936 

TABLE 2.-Composition of different types of organic matter · on basis of ultimate analysis · 

[Percent. Based mainly on same sources as table 1] 

Carbon Nitrogen Hydrogen Oxygen 

Peridineans ________ -- __ 45 3 7 45 

Diatoms ___________ - - __ 50 6 8 36 Copepods ______________ 50 10 8 32 

Average plankton _______ 48 5 8 39 

Soil fungL _____ :.. _______ 49 4 8 41 

Soil bacteria _________ '- _ 56 11 8 25 

Marine invertebrates ____ 48 11 7 34 VVorms ________________ 53 10 7 30 

Recent sediments _______ 52-60 6 7-8 25-35 

Ancient sediments __ - ___ 55-71 4 8-10 15- 30 

In recent marine sediments the organic matter 

should be essentially the same in composition as in 

the organisms that can live in the upper layers . of 

these sediments, such as marine invertebrates, and 

therefore the oxygen content of the organic matter 

should range chiefly between 25 and 35 percent. 

The deeper layers of sediment, which are inhabited 

mainly by bacteria, might be expected to have the 

minimunr content of 25 percent, but . the surface 

lay'ers, which are at or near the point of supply of 

organic matter from the overlying water, would probably have more nearly the maximum content of 3,5 

percent. The mean of the postulated minimum and 

maximum percentages-30 percent-seems the most 

reasonable single figure for the oxygen content of the 

organic constituents of marine clastic sediments at 

and shortly after the time of their deposition. . However, the quantity almost certainly differs considerably 

in different sediments. 

In ancient sediments the oxygen content of the 

organic constituents generally should be less than in 

recent sediments, because of the greater ease with 

which oxygen, as con1pared with carbon, can be lost 

from organic constituents under reducing conditions. 

Moreover, the oxygen · content would probably di~er 

among different sediments because of the different 

conditions to which the sediments have been subjected 

during and after lithification. 

The smaller content of oxygen in the organic constituents of ancient sediments, as compared with recent sediments, is indicated by the greater amount of 

chromic acid . the ancient sediments can reduce per unit 

of carbon. In this process of reduction both organic 

and inorganic constituents are oxidized, but most of 

the oxygen is used for oxidizing the organic substances. 17 

The quantity of oxygen requited to oxidize the sediments varies with the carbon content. The more oxygen consumed, the less is the state of oxidation (or 

the greater is the state of reduction) of the sediment. 

The ratio of the carbon content of the sediment to the 

quantity of chromic acid of standard strength that a 

11 Trask, P. D., and Hammar, H. E., Degrees of reduction and volatility as indices 

or source beds: Drilling and Production Practice, 1935, pp. 25(}-266, Am. Petroleum • 

Inst., 1936. 

given amount of the sedi.ment will reduce may be used 

as a m·easure of the state of oxidation (or reduction) of 

the sediment. A satisfactory form to use is the rati~ 

of the percentage of organic carbon in the organ~c : 

constituents of the sediment to the number of cubic 

centimeters of 0.4 ·normal chromic acid that can be 

reduced by 100' milligrams' of sediment. · The greater 

this ratio, the less is t;he oxygen required for oxidation· 

of the sediment and the greater the oxygen cbntent of 

the organic constituents. The nitio· is therefore a direct 

index of the oxygen content of the organic' constituents 

and hence is called the "oxidation factor." The oxida-· 

tion factor, however, cannot be used as an exact means 

of determining the oxygen content of the organic 

matter because of the uncertainty as to the aniouiit of . ' ' ' ' 

oxygen cons~med by the oxidation of the inorganic 

constituents of the sediments. ' '' ' 

The oxidation factor for ancient sediments· ranges 

. mainly between 0.75 and 1.20 a~d the average is approx-' 

imately 1.00. For recent sediments, according to dat·a: 

supplied by W aksman, 18 the factor is 1.20. · The higher. 

·oxidation factor for re·cent sediments indicates that 

their organic constit~ents ~ontain ·more oxygen ·'than 

those of ancient sediments. · · · 

. The oxygen content of :the ·organic · :matter can ·be· 

calculated from the oxidation factor if data 'are avail- . 

able t'o show the proportion of org:tnic' matter oxidiz~d 

and the proportion _of oxygen used fo'r oxidation of thf( 

inorganic constituents. In the . absence of accurate 

data on the' magnitude 'of these two variables it does· 

. not seem practicable in this paper to' attempt more than~ 

a rough calculation. The oxygen content of the orga:h~c 

constituents of rece!lt sediment's as estimated · from a 

~ompariso~ with living organisms ranges between 25' 

and 35 percent. · The oxygeri content of ancient sedi:.. 

· ments is materially less and, as indicated by the oxida'.:. 

• tion factor, may be 15 to 30 percent, or an average of 

, about· 23 percent. . · . . 

When these figures for the oxygen content a~e sub-

. stitu.ted in -the equation for calculating the oxygen 

· content from the oxidation factor, certain ~gures fof 

the proportion of organic matter oxidized and the pro-

, portion of oxygen required for oxidation of inorganic 

' constituents have to be assumed in orderto make the· 

: equation balance. As the assumed figu'res are reasori-' 

able and in accord with' known data, these estimates· 

. of the oxygen content of ancient sediments, though 

· questionable, are presumably -of the proper. order of 

. magnitude. · . · · ··' 

In a significant proportion of ancient sedimentS the 

oxidation factor is less than 0.85, which indicates that' 

the oxygen content of their organic constituents is' 

considerably below the average, perhaps as low as 

15 percent. 'rhe hypothesis should be considered that 

such reduced sediments may be more favorable source 

beds than sediments of average reduction. The re1s Waksman, S. A., personal communication. 
INFERENCES ABOUT THE ORIGIN OF OIL 153 

search project on source beds now being carried on by 

the United States Geological Survey and the American 

Petroleum Institute includes an intensive study of the 

relation of the oxidation factor to the occurrence of 

oil, to see if this factor can be used as an index of source · 

beds. 19 

CONTENT OF CARBON, HYDROGEN, AND NITROGEN 

If the amount of oxygen in the organic constituents 

is known the percentages of the other major constituents-carbon, hydrogen, and nitrogen-can be calculated readily. 

In the average plankton the ratio of hydrogen atoms 

to carbo~ atoms is about · 1.9. (See table 1.) In 

marine invertebrates the ratio ranges from 1.66 to 1. 76 

and the average is 1.7. As the marine invertebrates as 

a class feed on the plankton, it would appear that the 

planktonic organic matter loses hydrogen with respect 

to carbon in being transformed into the protoplasm of 

the animals that feed upon it. In soil bacte~ia, which 

may be considered analogous to marine bacteria, the 

of the organic matter; the weight of the carbon, therefore, is (100-30)-+-1.25==56 percent; hydrogen, being 

0.14 times the carbon, is 8 percent; and nitrogen, being 

0:11 time·s the carbon, is 6 percent. (See table 3.) In 

average ' ancient sediments oxygen is assumed to be 23 

percent of the total weight · of the organic matter,. 

whence carbon is64 percent, hydrogen 9 percent, and 

nitrogen 4 percent. In reduced ancient sediments, 

where the oxygen may be as low as 15 percent, carbon 

is 71 percent, hydrogen 10 percent, and nitrogen 4 

percent. 

TABLE 3.-Ratio of organ£c matter to carbon in different types of 

organic matter in sediments 

Percent by weight Ratio of 

organic- matter 

Carbon Hydro- Oxygen Nitro- to car- gen gen bon 

--- -------

Plankton ________________ 48 8 39 5 2. 1 

Recent sediments ___ _____ 56 8 30 6 1.8 

Ancient sediments _____ ___ 64 9 23 4 1.6 

Reduced ancient sediments_ 71 10 15 4 1.4 

ratio of hydrogen atoms to carbon atoms is 1.65. Bae- • 

tei-ia feed upon the organic matter at a later stage than CHANGES IN COMPOSITION WITH RESPECT TO TIME 

inv-ertebrates, and the composition of the bacteria is As the total quantity of organic matter· represented 

similar to that of the organic substances upon which by the original planktonic source decreases in the coursethey feed. 20 It therefore seems probable that in the . of time, the relative proportions of · its constituents 

organic constituents of recent sediments the ratio of change. The oxygen content of the organic constituhydrogen atoms to carbon atoms should be of the same · ents decreases from 39 percent in plankton to 15 perorder of ruagnituqe as in bacteria and bottom-living cent in . reduced ancient sediments. Carbon increases 

organisms-namely, about 1.7-though the ratio pre- from 48 to 71 percent. · Hydrogen increases from 8 to 

su.mably v-arie~ among different sediments. The hy- 10 percent . . Nitrogen is 5 percent in plankton, 6 perdrogen content, accordingly, can be estimated by multi- cent in recent sediments, and 4 percent in ancient 

plying the carbon content by the factor 1. 7. In the sediments. These quantities of carbon, hydrogen, 

absence of evidence to the contrary the ·same ratio can oxygen, and nitrogen refer to the average percentage 

be used tentatively for ancient sediments. As carbon by weight of the particular type of organic matter, not 

is 12 times as heavy as hydrogen, the relative weight to the proportions of the original quantity of ·organic 

of the hydrogen is 1.7-+-12 or 0.14 tinies the weight of matter in the plankton. · 

the carbon. Table 3 shows the relative changes in the carbon, 

In recent sediments the ratio of the weight of carbon · hydrogen, oxygen, and nitrogen as the organic matter 

to nitrogen is about 9; 21 accordingly, the weight of the ' diminishes. The main change is the progressive loss 

nitrogen is 0.11 times the weight of the carbon. In of oxygen with respect to the other ·constituents. As 

ancient sediments the carbon-nitrogen ratio seems to . the proportion of oxygen decreases, the proportions of 

range mainly between 13 and 20 and to average about carbon and hydrogen necessarily increase. The increase 

17; 22 the weight of the nitrogen is therefore 0.06 times in nitrogen from 5 percent in plankton to 6 percent in 

the weight of the carbon. . recent sediments is mainly a mathematical consequence 

Thus, the combined weight of the carbon, hydrogen, of the decrease in oxygen and implies no real increase 

and nitrogen in recent sediments is 1.0+0.14+0.11 = . in nitrogen; but the decrease to 4 percent in the ancient 

1.25 times the weight of the carbon, and in ancient : sediments indicates · a relative loss of nitrogen during 

sediments it is 1.00+0.14+0.06 = 1.20 times the weight . burial of the sediments. 

of the carbon. In recent sediments the weight of the : The changes in the nature of the organi~ matter 

oxygen is ~stimated to be 30 percent of the total weight i during the course of time may be illustrated more 

19 Trask, P. D., and Hammar, H. E., op. cit., pp. 25Q-266. 

20 Waksman, S. A., Principles of soil microbiology, pp. 377-383, Baltimore, 

Williams, Wilkins Co., 1927. 

21 Trask, P . D., Origin and environment of source sediments of petroleum, p. 21, 

Houston, Tex., Gulf Publishing Co., 1932. 

22 Trask, P . :b., and Haw,mar, H. E., Organic content of sediments: Drilling and 

Production Practice, 1934, p. 118, Am. Petroleum Inst., 1935. Also data in a paper 

to be published in Drilling and Petroleum Practice, 1936. 

· clearly if the composition is expressed in terms of 

· atomic ratios rather than as percentag~s by weight. 

The percentages given in table 3 have been recalculated 

; as atomic ratios and reduced to a common denominator 

' in table 4. Throughout this series· the carbon content 

has been arbitrarily taken as 18. According to this 
154 SHORTER CONTRIBUTIONS 'TO GENERAL GEOLOGY, 1936 

calculation hydrogen decreases from 34 in average 

plankton to 31 in recent and ancient sediments. 

· Oxygen decreases from 11 in plankton to 7 in recent 

sediments and to 3 in reduced ancient sediments. 

Nitrogen decreases from about 2 in plankton to 1 in 

ancient sediments. Thus the organic matter as it 

changes from plankton to organic constituents of 

ancient sediments loses most of its oxygen and a considerable part of its nitrogen. It must be borne in 

mind, however, that the figures for the atomic ratios 

are based on general averages and that the ratios may 

vary considerably among individual sediments. . 

TABLE 4.-Atomic ratios of constituents of different types of · organic matter in sediments 

Carbon Hydro- Oxygen Nitro- gen gen 

---- -----

Plankton __ ___________ _____ ____ 18 34 11 2 

Recent sediments __ _____ ________ 18 31 7 2 

Ancient sediments _______ ____ __ _ 18 31 5 1 

Reduced ancient sediments ___ ___ 18 31 3 1 

RATIO OF ORGANIC MATTER TO CARBON IN 

SEDIMENTS 

The determination of the total quantity of organic 

matter in sediments is an essential step in the study of 

source beds. The. common procedure for estimating 

the organic content is to determine the carbon content 

and multiply it by a factor which is the reciprocal of 

the proportion of carbon to . total organic matter. 

This factor naturally differs for different types of sediments and for different types of organic matter. It 

has been calculated for each of the four groups of 

organic matter considered in this report. 'For plankton 

it is 2.1, for recent sediments 1.8, for ancient sediments 

1.6, and for reduced ancient sediments 1.4. (See 

table 3.) 

In previous work 23 the writer has assumed a ratio 

of 1. 7 for recent sediments, which is the same that soil 

chemists have used for many years for soils. Recently Alexander and Byers 24 have questioned' the 

propriety of a single ratio of 1. 7 and have -pointed out 

that the ratio varies considerably among different soils. 

They have suggested that 1.93 is probably the most 

satisfactory single factor. Waksman 25 has proposed 

the factor 1.92 for recent marine sediments and . ' 

Potonie and Reunert 26 present data that indicate the 

factor 1.83 ·for certa.ln recent lacustrine sediments in 

Germany. 

2a Trask, P. D., Origin and environment of source sediments of petroleum, p. 18, 

Houston, Tex., Gulf Publishing Co., 1932. 

24 Alexander, L. T., and Byers, H. G., A critical laboratory review of methods 

of determining organic matter and carbonates in soil: U. S. Dept. Agr. Tech. Bull. 

317, pp. 1-24, 1932. 

25 Waksman, S. A., The role of bacteria in the cycle of life in the sea: Sci. Monthly, 

vol. 38, pp. 35-49, 1934. · 

26.Potonie, R., and Rennert, D., Geologis.ch-chemische Untersuchungen von 

Sapropelen qes Unteriicker und Sakrower Sees: Schriften aus dem Gebiet der 

Brennsto:ff-geologie, Heft 10, pp. 149-169, 1935. 

Organic constituents of recent sediments, ·being 

always submerged in water, should usually be more 

reduced than those of soils, which are not always completely saturated with water. The ratio of organic 

matter to carbon in recerit ·sediments, therefore, would 

as a rule probably be less than in soils. Consequently, 

a ratio of 1.8 presu:mably would be betterthan 1.9. 

In the absence of data to the contrary the writer 

in previous work 27 assumed that the ratio in· ancient 

. sediments was 1.5. According to the data given in 

table 3, the ratio 1.6 would be better for general use for 

ancient sedi:ments and 1.4 for reduced ancient sediments. 

The writer presents these ratios of organic matter to 

carbon content very tentatively. In orde:r; to estimate 

the organic content of sediments it is necessary to use 

some kind of a ratio of this type. At present, the ratio 1 of organic matter to carbon see:ms the most practicable, 

and according to available data the figures given here 

seem the hlOSt satisfactory. 

INTERPRETATION OF DATA 

POSSIBLE SOURCE MATERIALS 

General character and relative quantity of organic 

material.-The foregoing attempt to discuss quantitatively the changes in the organic constituents of 

sedi:ments during the course of their history seems to 

indicate rather clearly that only a very small proportion of the original organic matter . generated by the 

plankton actually accumulates in. sediments, and that 

organic constituents buried a few inches in. the muds 

· on the sea bottom do not thereafter decrease greatly in 

quantity. 

The organic constituents in sediments consist chiefly 

of complex resistant compounds, which with respect to 

their original planktonic source are chemically reduced 

. in,that they contain comparatively little oxygen. The 

· relatively elementary substances such as sugars, celluloses, fats, and simple proteins, of which the original 

· plankton is mainly composed, are decomposed or 

altered to a considerable extent during the process of 

deposition and probably occur in sediments in quantities so small that they are not likely to be major 

sources of petroleum. 

In most oil fields the proportion of the organic matter 

that is converted into petroleum is difficult to ascertain. In the Santa Fe Springs field of California the 

proportion is probably about -;1: percent, though it may 

be as low as 2 percent or as high as 15 percent.28 In 

other fields the amount transformed into oil :rp.ay be 

less, but as the sediments in the Santa Fe Springs fieid 

21 Trask, P. D., Results of the American Petroleum Institute research project on 

origin and environment of source beds of petroleum: Am. Petroleum Inst. Production 

Bull. 211, pp. 19-31. 1933. 

2s Trask, P . D., Proportion of organic matter converted into petroleum in Santa Fe 

Springs field, Calif.: Am. Assoc. Petroleum Geologists Bull., vol. ·20, pp. 245-257, 

1936. 
INFERENCES ABOUT THE ORIGIN OF OIL 155 

are mainly Pliocene and hence relatively young, the 

figures given are presumably minimum figures. Any 

constituent present in an amount less than 1 or 2 

percent of the organic matter, therefore, in all pro-bability cannot be a major source of petroleum. 

Cellulose.-The three main constituents of the original planktonic protoplasm are carbohydrates, fats, and 

proteins, but by the time the derived organic materials 

are deposited in the sediments their nature has changed 

considerably. Cellulose, though perhaps constituting 

14 perceht of the original plankton, ordinarily is found 

in amounts of 1 percent or less in recent marine sediments.29 Many sediments contain no measurable 

trace of cellulose, and the maximum observed was in 

a shallow lagoon deposit, where it was 5 percent of the 

organic constituents. In recent marine sediments the 

cellulose decreases in quantity from the surface downward, and in ancient sediments it is usually not present 

at all.30 

Because of the small quantity of cellulose found in 

sedinients, therefore, it does not seem probable that 

petroleum is derived mainly from the cellulosic constituents of the sedin1ents, as advocated by 1

Berl.31 

However, as the original planktonic source material 

may contain as much as 14 percent of cellulose, it is 

possible that some of the mother substances of petroleum in sediments may be derived from cellulose .. 

Other carbohydrates.-Other carbohydrates, such as 

hemicelluloses, starches, and sugars, are present in 

recent sediments in as small quantities as celluloses, 

and hence in all likelihood they are not major sources 

of oil. The organic constituents present in the sediments, however, may be derived to a considerable 

extent from carbohydrates of these types in the 

original planktonic protoplasm. T~e pentoses, because of their similarity to ring compounds, such as 

naphthenes., have been postulated as "possible mother 

substances of petroleu:m,32 but they a1so . seem to be 

present in sediments in quantities too small to be a 

main source of oil. 

Proteins.-Proteins can be considered as possible 

source material, as nitrogenous compounds form about 

40 percent of the organic constituents in recent sediments and 27 percent in ancient sediments.33 These 

nitrogenous compounds are derived largely from 

proteins ;in the basic planktonic organic matter, but 

the proteins in the sedi:ments consist mainly of complex 

resistant co:mpol._lnds that apparently differ considerably from the proteins in the original plankton. 

Petroleum contains appreciable quantities of combined 

29 Trask, P. D., Origin and environment of source sediments of petroleum, p. 302, 

Houston, Tex., Gulf Publishing Co., 1932. 

ao Idem, pp. 2D0-218. · 

31 Berl, E., Origin of asphalt, oil, natural gas, and bituminous coal: Science·, new 

ser., vol. 80, pp. 227-228, 1934, 

32 Brooks, B. T., The chemical evidence for the low-temperature history of 

petroleum: Inst. Petroleum Technologists Jour., vol. 20 ,pp. 177-205, 1934. 

33 Trask, P. D., op. cit. ,p. 200. 

nitrogen, though the proportion ordinarily is less than 

in the organic constituents of the sediments from which 

the oil see:ms to be derived. 

Simple proteins are present in recent marine ·sediments in quantities so s:mall that they probably should 

not be considered as :major sources of oil. The average 

quantity of simple water-soluble proteins in the upper 

layers of recent :marine sediments is about 3 percent 

of the organic :matter.33 This protein content in part 

may represent the protoplasm of micro-organisms living 

in the sediment and therefore :may be destroyed or 

considerably :modified after death of the organisms. 

Simple proteins terid to decompose rather readily in 

sediments and in the overlying water.34 Therefore, if 

petroleum is derived from proteins, it presumably 

comes from the more resistant, complex nitrogenous 

compounds. 

Fats.-Fatty substances have been regarded by 

many writers 35 as the :main source of petroleum, but 

this hypothesis :may not be correct. The chief reasons 

for believing that· oil is derived from fatty substances 

are the low oxygen content of fatty materials and their 

similarity in composition to paraffin hydrocarbons. 

However, fats are chain compounds; all petroleums 

contain . an appreciable proportion of ring compounds, 

and many petroleums contain more ring compounds 

(naphthenic, polycyclic, and benzenoid) than chain 

compounds (paraffenic).36 Fatty materials are either 

saturated or unsaturated; petroleum is composed 

almost entirely of saturated substances.37 The iodine 

number of the fatty substances found in marine 

animals and plankton ranges chiefly between 110 and 

120; 38 in most crude oils the iodine nu:mber is less 

than 20, and in some it is as low as 2.39 As the iodine 

number is an index of the degree of unsaturation of 

fatty and oily substances, the fatty materials that 

eventually are deposited in sediments evidently are 

much more unsaturated than the compounds ordinarily 

present in crude oil. 

Consequently, if petroleum is derived mainly from 

fats, some special process such as polymerization has 

to be invoked to account for the formation of the ring 

compounds and the al:most · complete absence of 

unsaturated compounds. If polymerization or some 

other process has to be assumed, why limit the source 

to fatty materials? Other organic substances, in all 

probability, cou~~ serve as well as fats. 

34 Hecht, F., Der Verbleib der organischen Substanz der Tl::re bci meerische 

Einbettung: Senckenbergiana, Band 15, pp. 165-249, 1933. Jensen, P. B., Studies 

concerning the organic matter of the sea bottom: Danish Bioi. Sta. Rept. 22, pp. 

1-39. 1915. 

35 Notably Engler, C., and Hofer, H., Das Erdol, Band 2, pp. 59-146, 1909. 

a6 Gruse, W. A., Petroleum and its products, pp. 4, 36, New York, McGraw-Hill 

Co., 1928. . , 

a; Sakhanov, A .. and Wirabianz, R., Die chemische Zusammensetzung der ErdOle 

der U. S. S. R.: Petroleum, Band 25, pp. 867-892, 1929. 

as Rosenfeld, G., Studien tiber das Fett der Meeresorganismen: Wiss. Meeres-

. untersuchungen, neue Folge, Abt. Helgoland, Band 5, pp. 57-84, 1904. 

a9 Sakhanov, A. and .Wirabianz, R.,op. cit., pp. 877-882. Gruse, W. A., op. cit., 

pp. 27-32. Gurwitsch, L., The scientific principles of petroleum technology, trans. 

lated and revised by H. Moore, pp. 28-33, London, Chapman & Hall, Ltd., 1926. 
156 SHORTER CONTRIBUTIONS TO GEN:ERAL GEOLOGY, 1936 

Another argument against the derivation of oil from 

fatty substances is the chemical stability of such substances.40 Large quantities of fatty and waxy rna.;. 

terials (which contain fatty acid radicals) are present 

in oil shales of continental origin, yet oil shales of this· 

type are associated with very few oil fields. 

Flirthermore, fats-that is, fatty materials soluble 

in carbon tetrachloride-form less than 1 percent of 

the organic content of recent marine sedimentsn and 

therefore· apparently are present in quantities too small 

to be a major source of oil. . Other fatty materials, . 

such as metallic soap or waxes, may be present in 

sediments in larger amounts than fats. 42 Fatty materials tend to ionize in water, and in the presence of 

an excess of metallic ions they are precipitated as 

soaps. No data are yet available on the quantity ·of 

·· metallic soaps in sediments. Metallic soaps may possibly be present in sufficient amounts to account for 

the oil, but if they exist in such quantities the problem 

still remains as to how they can be. transformed into 

naphtbenic and other ring compounds.· 

Other substances:-Cellulose, carbohydrates, simple 

proteins, and fats, which form the major part of the 

organic constitutents of the planktonic source material, 

are so · much altered in the course of deposition that 

they form not more than 5 percent of the organic 

constituents of sediments and therefore are present in 

quantities probably too small to be main sources of 

petroleum. The oil evidently must come from the 

. remaining 95 percent of the organic matter-the indigestible residues that probably consist mainly of complex compounds and are relatively deficient in oxygen. · 

Petroleum in several areas in the United States is 

associated with sediments whose organic constituents 

are comparatively low in oxygen.43 · 

ORIGIN OF OIL 

The complex residual substances that constitute the 

main part of the organic matter in sediments may 

contain loosely attached radicals of chain or ring structure. Under favorable conditions, perhaps aided by 

polymerization or methylation/4 these loosely attached 

radicals may become separated from their parent substances and form liquid hydrocarbons. One of the 

conditions that might favor . such a process is the 

_ tendency of the organic constituents of sediments to 

come to chemical equilibrium after the sediments have 

40 Brooks, B. T., The chemical evidence for the low-temperature history of petroleum: Inst. Petroieum Technologists Jour. vol. 20, p. 185, 1934. 

•• Trask, P. D ., Origin and environment of source sediments of petroleum, p. 200, 

Houston, Tex., Gulf PubliShing Co. 1932. 

42 Trask, P. D., Results of distillation and other studies of the organic nature of 

soine modern sediments: Am. Assoc. Petroleum Geologists Bull., vol. 11, p. 1228, 

1927. Wells, R. C., and Erickson, E. T., The analysis and composition of the fatty 

material pro'duced by the de'composition of. herring in sea water: Am. Chern. Soc. 

Jour. vol. 55, p. 338-341, 1933. 

43 Trask, P. D., and Keyte, W. R ., Degree of reduction of sediments in the east 

Texas basin as an index of source beds: Oil Weekly, vol. 81, no. 10, pp. 6Q-70, May . 

18, 1936. -

H Pratt, W. E., Hydrogenation ·and the origin of oil: Problems of Petroleum 

Geology, pp. 235-245, Tulsa, Okla., Am. Assoc. Petroleum Geologists, 1934. 

· been buried bey~nd the limit of effective microbial 

action. Individual organic substances·· found in sediments may be relatively stable in a free state but not 

stable when pressed in close contact with other organic 

substances in. a sediment. If they are unstable with 

respect t_o adjoining organic materials they will · tend 

to reach a stable state, and liquid hy;drocarbons .may 

possibly ·be formed as a result of the readjustments 

that take place as .. the· organic constitl).ents endeavor to 

come into equilibrium. _.As _ the residual organic -substances consist mainly of solids and,are largely i:nsolubl~ 

in water, the chemical changes caused in .this manner 

- would take place very slowly as compared with chang~s 

resulting from· 'the activities _·of org~nisms. · 

While the organic constituents ·are in the overlying 

water or in the ·upper layers of sediments, alterations 

caused by living things greatly · predominate .· over 

changes caused by purely physical and chemical agen-' 

cies. In such environments the organic substances 

have less physical contact with' one another and are, 

therefore, less susceptible to ·purely chemical (nqnbiologic) changes than when in the deeper layers of sedi7 · 

ment, where they are. firmly pressed together. . Consequently, they would have relatively little tirne to corqe 

into chemical equilibrium ·with . one another . before 

they would be attacked by some living organism. ·: ~ · 

As the sediments become buried de·eper .and -deeper, 

the activity of living -organisms becomes progressively 

less, and ultimately a depth is· reached where -the 

changes in the organic matter resulting from the activ7 

ity of organisms becomes . relatively insignificant. ~ 

The sediments thenceforth are dominated by purely, 

physical and chemical agencies, and the . organic con-

. stituents proceed toward ·effecting a state :.of equilibriu-m. A st~te of complete equilibrium, however, 

might never be attained because of the effect of chang~s 

in temperature and pressure- to which. the sediments 

may be subjected during the course of time.. . 

As soon as· liquid hydrocarbons were :generated,' they 

would form an oily phase insoluble in water-the ·ances.:. 

tral pe_troleum. Certain organic constituents, such as 

some of the pigments, waxes, and fatty acids that 

hitherto had existed in the solid state, would be solp.ble 

in thi::l oily liquid. Organic substances that -lay ·near 

the place where the oil was firs't fo.rmed might be 

dissolved before the ancestral -petroleum migrated~ 

Other substances that lay in the path of the migr~ting 

oil ·might be dissolved later. The opticaJly active .;onstituents of petroleum might . to some· extent be · due to 

such a process. The similarity between certain organic 

pigments in ancient and modern sediments -

46 suggests 

that some substances, after being dissolved by the l •I I 

45 White, David, Geology and occurrence of petroleum in the United States: Petroleum investigation, pt. 2 (73d Cong., H. R., Comm. on. Interstate and. Foreign Commerce, Hearings on H . Res. 441), p. 901, 1934. 

46 Dhere, C., and Hradil, G., Fluoreszenzspektrographische Untersuchungen aJ;l 

Oelschiefer: Schweizer. niin.-pet. Mitt., Band 14 . pp. 279-295,, 1934 · 
INFERENCES ABOUT THE ORIGIN OF OIL 157 

ancestral petroleum, might persist in a relatively unchanged condition for a long time. 

As soon as any materials were dissolved, the equilibrium relations of the constituents of the ancestral 

petroleum would be altered, and these constituents 

would tend to readjust themselves in an effort. to come 

to a stable condition. As the oil migrated and dissolved new constituents, its composition would be subject to continued change. Even after it reached the · 

reservoir, it seems evident that it would slowly alter 

until a final stable condition was reached. Such a 

concept is in accordance with the progressive paraffination of crude oils advocated by Barton.47 Nevertheless, an ultimate state of complete equilibrium may 

never be attained. If the conditions of heat and presli Barton, D. C., Natural history of Gulf coast crude oil: Problems of Petroleum 

Geology, pp. 109-155, r.rulsa, Okla., Am. Assoc. Petroleum Geologists, 1934. 

0 

sure should change while the ancestral petroleum was 

in the process of developing into crude oil, new conditions of equilibrium might be set up, and consequent 

readjustments in composition· would ensue. 

This discussion of the origin of oil by physicochemical 

readjustment of the organic constituents of sediments 

is incomplete in that it does not consider what particular types of organic substances are likely to he transformed into oil, but it seems inadvisabie to speculate 

further in the study of possible source material until 

more detailed information is available on the chemical 

nature of the organic constituents of sediments. The 

most favorable mother substances of petroleum are 

presumably compounds deficient in oxygen. Additional data on the chemical composition of possible 

source materials of petroleum are urgently needed. 

I•