Hydrocarbon source potential of organic facies of lacustrine Elko formation (Eocene-Oligocene), northeastern Nevada
The Elko Formation, an Eocene-Oligocene lacustrine deposit cropping out in northeastern Nevada, is composed of two distinctly different organic-rich facies: a lignitic, gas-prone siltstone and an oil shale. A third organic-lean facies is represented by mudstones containing small amounts of fine-grained reworked kerogen. The deposit is thermally immature with respect to oil generation. Geochemical indicators of the two major organic facies are distribution of steranes and diterpanes, presence or absence of a specific triterpenoid biomarker (gammacerane), kerogen form, and Rock-Eval pyrolysis parameters, S/sub 2//S/sub 3/ and (S/sub 1/ + S/sub 2/)TOC. The siltstones are characterized by: (1) vitrinitic kerogen, (2) pristane/phytane ratios slightly greater than 1.0, (3) relatively less negative delta/sup 13/C values for kerogen and C/sub 15//sup +/ hydrocarbons, (4) a predominance of C/sub 29/ steranes and small amounts of rearranged steranes, (5) primarily C/sub 19/ and C/sub 20/ tricyclic diterpanes, and (6) a predominance of 17..beta..(H)-22,29,30-trisnorhopane with respect to 17..cap alpha..(H)hopanes and 17..beta..(H) moretanes. The oil shales are characterized by:(1) algal kerogen, (2) pristane/phytane ratios less than 0.5, (3) relatively more negative delta/sup 13/C values for kerogen and C/sub 15/+ hydrocarbons, (4) a mixture of C/sub 27/, C/sub 29/ steranes and 4-methyl steranes, (5) a mixture of C/sub 19/ to C/sub 26/ diterpanes, and (6) a predominance of hopane and moretane and the presence of gammacerane. Hydrous pyrolysis of solvent-extracted oil shale produced a waxy oil-like bitumen whose more mature biomarkers and stable carbon isotopic composition resembled the unreacted oil shale.
- Research Organization:
- Cities Service Oil and Gas Corp., Tulsa, OK
- OSTI ID:
- 5589973
- Report Number(s):
- CONF-8408161-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 68:7; Conference: Energy and More in '84, Salt Lake City, UT, USA, 27 Aug 1984
- Country of Publication:
- United States
- Language:
- English
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