Occurrence of Biogenic Steranes and Pentacyclic Triterpanes in an Eocene Shale (52 Million Years) and in an Early Precambrian Shale (2.7 Billion Years): A Preliminary Report

Abstract

Thus far, our search for molecular carbonaceous remnants, specifically indicative of biogenic processes, has been epitomized by the isolation and identification of isoprenoid alkanes in a number of ancient sediments of various geologic types ranging from several million to over 2.7 billion years in age.'-3 We have felt that the isoprenoid alkanes could serve as "biological markers" in our quest for evidence of life among geologically well-characterized ancient shales and oils, and more specifically in carbonaceous chondrites.Earlier we reported preliminary studies on the oil shale from the Green River Formation (Eocene age, about 52 X 106 years) at Rifle, Colorado.' 2 These results, which paralleled those of Cummins and Robinson,4 established the biological history of this Cenozoic rock from the very uneven distribution of the n-alkanes and from the presence of large proportions of isoprenoid alkanes [C16-, C18-isoprenoid; C19isoprenoid (pristane); C20-isoprenoid (phytane)].We wish to report now the isolation and identification of the C27-, C28-, and C29steranes and a C3o-pentacyclic triterpane from the branched-cyclic alkane fraction of the Green River Shale. Separation of the branched-cyclic alkane fraction (extraction from shale previously described in detail2) into its individual components was achieved by an initial programed gas-liquid chromatographic run to 3000 (3% SE-30 on Gaschrom Z, 100-120 mesh, 10 ft X 1/4 in. s.s. column, program rate 40 per min) in which peaks were collected and in turn rechromatographed isothermally at temperatures ranging from 2600 to 280°(1% SE-30 on Gaschrom Z, 100-120 mesh, 10 ft X 1/4 in. s.s. column). Mass spectra of these collected samples were determined in a direct inlet system of a modified C.E.C. 21-103C mass spectrometer.' A preliminary mass spectral examination of the fractions collected as indicated in Figure 1 from a programed run revealed the molecular weights which are listed in Table 1 for the major components. From the subsequent isothermal separations, a homologous series of compounds were isolated which display mass spectral fragmentation patterns characteristic of the saturated, tetracyclic sterane carbon skeleton

The organic geochemistry of ancient sediments—Part II

“…Representative samples were examined in a direct inlet system (Burlingame, 1965). In the case of more volatile fractions like those containing the C16 isoprenoid alkane, the probe used for introduction of the sample \~as cooled with liquid nitrogen to avoid pumping off small s~)les.…”

Research Status and Progress of Genetic Mechanism of Abnormal Regular Sterane Distribution in Geological Bodies

“…C 27 , C 28 and C 29 steranes were first identified in the American green river and Pre-Cambrian shale by Burlingame (1965) [1]. Then, Eglinton and Calvin (1966) [2] and Eglinton and Murphy (1969) [3] further confirmed the existence of cholestane, ergostane and sitostane.…”

Crude Petroleum

“…The greater the complexity of such molecules the more information they are likely to convey. Terpenoid hydrocarbons fulfill all of these requirements and the recognition of the precise molecular structure of petroleum steranes [192] and triterpanes [78] would appear to be important since the information contained in their molecular skeletons may well be biologically more specific than that contained in the isoprenoid alkanes. These petroleum steranes and triterpanes appear in abnormal concentration and seem to be chiefly responsible for the high specific rotations of petroleum distillates boiling in the region of 475 0 C [78].…”