Petroleum Source Rock Evaluation of the Cretaceous Newark Canyon Formation in North-Central Nevada
MULLARKEY, J. C., Colorado School of Mines, Golden, CO, J. L. CLAYTON, U.S. Geological Survey, Denver, CO, R. F. WENDLANDT, Colorado School of Mines, Golden, CO, and T. A. DAWS, U.S. Geological Survey, Denver, CO
The petroleum source rock potential of the Cretaceous Newark Canyon Formation, Eureka and Elko counties, Nevada, has been determined by integrated field and subsurface sampling and mapping and by geochemical analyses. To supplement geologic mapping we measured a reference stratigraphic section and made four gamma-ray traverses to help correlate poor exposures. Cores and cuttings from three wells provided subsurface control for the organic-rich part of the section. Sixty-six outcrop and ten subsurface Newark Canyon samples were collected and pyrolyzed (Rock-Eval II) to determine hydrocarbon yield, total organic carbon content (TOC), and thermal maturity. Through solvent extraction, two samples were prepared for gas chromatography and mass spectrometry analyses used to evaluate the envi onment of deposition.
The Newark Canyon Formation is 2055 ft thick in the Cortez Range, comprised primarily of conglomerates and sandstones with 115 ft of intercalated limestone and calcareous shale in the upper 650 ft. The limestone and shales average 2.5 wt. % TOC, consisting of type II/III kerogen (hydrogen indices 7-424 mg hydrocarbon/g TOC). The correlative section in the Pinon Range contains approximately 200 ft of calcareous shale that averages 8% TOC and has as much as 23.5% TOC, representing type I/II kerogen (hydrogen indices 457-912 mg hydrocarbon/g TOC). Organic content and kerogen type in subsurface samples are similar to that of the Cortez Range samples. The Newark Canyon Formation is marginally mature to mature with respect to petroleum generation (average Tmax values = approximately 440 deg ees C and vitrinite reflectance values between 0.53 and 0.78). Terpane and sterane abundance and transformations suggest Newark Canyon Formation outcrops are marginally mature.
These data distinguish the Newark Canyon Formation as an excellent potential source rock. Saturated hydrocarbon distributions and transmitted light microscopy confirm field observations that the Newark Canyon's organic-rich facies was deposited in a low-energy lacustrine environment.
AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)