480 



UNITED STATES MINERAL RESOURCES 



of photosynthetic organisms was derived (Treibs, 

 1936; Orr and others, 1958; Dunning, 1963). Fur- 

 thermore, the evolution of an impressive series of 

 alkanes (methane through pentane) by low tem- 

 perature pyrolysis from ether-insoluble organic mat- 

 ter (kerogen) extracted from this same stratum 

 (Hoering, 1967, p. 97 and table 4) indicates that the 

 seepage petroleum (first reported by White and 

 Wright, 1954) from the White Pine Copper mine is 

 almost certainly younger Precambrian in age, and 

 the Nonesuch shale is its ancient source rock. Car- 

 bon isotope ratios from the soluble and the insoluble 

 fractions of the Nonesuch organic matter are almost 

 identical and diagnostically biosynthetic (Hoering, 

 1967, table 8) and further strengthen this conclu- 

 sion. Negative results were reported by Hoering 

 from his attempts to detect optical activity (rota- 

 tion in the Nonesuch petroleum by "... a factor of 

 50 less than has been reported from Paleozoic 

 petroleums.") The likelihood that polycyclic, satu- 

 rated hydrocarbons are responsible for some of the 

 optical rotation so characteristic of younger petro- 

 leums (Oakwood and others, 1952; Hills and others, 

 1970) and that sterols are precursors of such com- 

 pounds takes on special interest in view of the fact 

 that anaerobic organisms do not produce highly 

 unsaturated fatty acids or sterols (Bloch, 1965). 



Many other occurrences have been reported (Vas- 

 soyevich and others, 1971; Murray, 1965) of possi- 

 ble, probable, and undoubted Precambrian hydro- 

 carbons from many localities in the world, but none 

 is as thoroughly documented by pertinent observa- 

 tional and analytical detail as the occurrence in the 

 Nonesuch shale. Of these other occurrences, the 

 oldest that appears to be fairly certainly indigenous 

 is 1.2 b.y. (saturated paraffinic compounds extracted 

 from "Muhos shale" of the Jotnian series, Finland — 

 Hoering, 1967, p. 98-100), and most are from 

 youngest Precambrian rocks. Of further interest is 

 the fact that only one undoubtedly Precambrian 

 occurrence has resulted in commercial hydrocarbon 

 production; that of gas, condensate, and oil from 

 the late Proterozoic multizone Markovo field in the 

 Irkutsk part of the western Siberian Angara- 

 Tunguska basin (Vassoyevich and others, 1971, p. 

 412-413). Commercial petroleum and natural gas 

 are almost exclusively products of sedimentary rocks 

 deposited during only the last one-eighth to one- 

 fourth of the earth's history, that part during which 

 an atmosphere rich in oxygen prevailed and during 

 which complex multicellular organisms developed. 

 Carbon is the stuff of life! 



The evidence has been summarized which indi- 

 cates that hydrocarbon compounds are quite scarce 



in rocks of Precambrian age, even those relatively 

 rich in organic carbon and kerogen, and that fluid 

 hydrocarbons (commercially producible or not) are 

 extremely rare in such strata and are restricted thus 

 far to rocks of late Proterozoic age. It is self evi- 

 dent, then, that most of the earth's hydrocarbons 

 must occur in rocks of Phanerozoic age and in Holo- 

 cene sediment (plus the biosphere and hydrosphere) . 

 Qualitatively at least, the long-term increase in 

 organic carbon concentrations of clays of the Rus- 

 sian Platform appears to be paralleled by a world- 

 wide increase in hydrocarbon concentrations from 

 late Precambrian to Mesozoic and Tertiary rocks. 

 Whether these relationships result primarily from 

 temporal variations in the primary productivity of 

 the ancient biosphere, or whether other time- 

 dependent factors intervene and override, such as 

 diagenetic (metamorphic) modifications of the hy- 

 drocarbon precursors in sedimentary organic mat- 

 ter or erosional, structural, or thermal events that 

 reduce sedimentary rock volume, rock porosity, or 

 the effectiveness of hydrocarbon traps, remains to 

 be examined quantitatively Quantitative data are 

 needed regarding variations in the hydrocarbon con- 

 centrations of Phanerozoic rocks as a function of 

 geologic age and depth of burial (thermal history). 

 Unfortunately, only a start has been made toward 

 that goal, and that only coincidentally as a result of 

 commercial prospecting for petroleum and natural 

 gas. 



PRODUCIBLE HYDROCARBON ASSESSMENT 



Compared with the tremendous efforts that have 

 been expended in the industrial search for commer- 

 cially producible fluid hydrocarbons (especially in 

 the United States and elsewhere in North America) , 

 the previously mentioned efforts to assess the or- 

 ganic carbon contents of sedimentary rocks, im- 

 pressive and valuable as they are, are completely 

 overshadowed. In the United States alone, more than 

 2,222,300 wells, totalling 7 billion feet of hole in 

 all (R. F. Meyer, oral commun., Jan. 25, 1973), 

 have been drilled in the search for petroleum and 

 natural gas. Most of those holes were located after 

 much deliberation, on the basis of substantial sci- 

 entific and technical data expertly evaluated. They 

 were drilled either to exploit hydrocarbon reservoirs 

 already known to exist from prior exploratory drill- 

 ing, or as "wildcats" with the specific objective of 

 evaluating scientific hypotheses advanced by tech- 

 nical advisors who suggested the possibility of find- 

 ing abnormally rich concentrations of hydrocarbons ; 

 concentrations large enough and sufficiently ener- 

 gized that part of the crude chemicals could be pro- 



