Recent studies by physicists, chemists, biologists, and geochemists have yielded new information which has important implications to concepts of petroleum evolution. For example, studies of carbon isotopes in sediments and crude oils suggest that terrestrial plants, instead of marine plants and animals, may be the principal primary substance from which petroleum is derived. Further, the discovery of hydrocarbons in Recent sediments demonstrated the early formation and availability of petroliferous materials in depositional basins. However, characterization has revealed differences in the nature and abundance of hydrocarbons in Recent sediments compared to crudes and ancient rocks, indicating that modification and formation of hydrocarbons during diagenesis may be essential for the development of a source rock.

The distribution and character of hydrocarbons in rocks of the Cherokee Group indicate that some environments generate more hydrocarbons than others, confirming the geologic opinion that there is a range of variation in the nature of petroleum source beds. However, studies of the Cherokee Group indicate that the recognition and evaluation of source rocks on the basis of absolute hydrocarbon content may be an oversimplification because the hydrocarbons may not be indigenous, or may have formed subsequent to primary migration, or that some rocks may have yielded only a small part of their hydrocarbons. Finally, comparison of crude oil-source rock pairs in the Cherokee Group indicates that the development of geochemical correlation techniques will be complicated because primary migration is inefficient, selective, and probably causes considerable modification of hydrocarbons en route.

The problem of petroleum evolution seems ripe for an integrated attack by geologists supported by physicists, chemists, biologists, and geochemists. The belief that an ultimate comprehension of petroleum evolution can only be developed by the interpretation of experimental and analytical data on a sound geological basis is the underlying philosophy of research on petroleum evolution in the Cherokee Group of southeastern Kansas and northeastern Oklahoma.

DONALD R. BAKER

Donald R. Baker is a graduate of California Institute of Technology (B.S., 1950), and Princeton University (Ph.D., 1955). He also attended the University of Oslo, Norway, as a Fulbright Student in 1950-51.

His professional experience includes work with the U.S.G.S., and with Northwestern University as an Instructor in the Department of Geology. Since 1956 he has been Research and Advanced Research Geologist with Marathon Oil Co. (formerly the Ohio Oil Co.) in the Denver Research Center. His exploration research has been primarily in the area of organic geochemistry.

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