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J. G. Palacas

Publications and source records attributed to J. G. Palacas.

6 recordsLinked to original sources
USGS1996

Source rock potential of middle Cretaceous rocks in southwestern Montana

The middle Cretaceous in southwestern Montana is composed of a marine and nonmarine succession of predominantly clastic rocks that were deposited along the western margin of the Western Interior Seaway. In places, middle Cretaceous rocks contain appreciable total organic carbon (TOC), such as 5.59% for the Mowry Shale and 8.11% for the Frontier Formation in the Madison Range. Most samples, however, exhibit less than 1.0% TOC. The genetic or hydrocarbon potential (S 1 +S 2 ) of all the samples analyzed, except one, yield less than 1 mg HC/g rock, strongly indicating poor potential for generating commercial amounts of hydrocarbons. Out of 51 samples analyzed, only one (a Thermopolis Shale sample from the Snowcrest Range) showed a moderate petroleum potenti l of 3.1 mg HC/g rock. Most of the middle Cretaceous samples are thermally immature to marginally mature, with vitrinite reflectance ranging from about 0.4 to 0.6% R 0 . Maturity is high in the Pioneer Mountains, where vitrinite reflectance averages 3.4% R 0 , and at Big Sky, Montana, where vitrinite reflectance averages 2.5% R 0 . At both localities, high R 0 values are due to local heat sources, such as the Pioneer batholith in the Pioneer Mountains.

Montana↗
USGS1986

Geochemical correlation of surface and subsurface oils, western Greece

Biodegraded seep oils, devoid of n -alkanes and most isoprenoid hydrocarbons, were successfully correlated with subsurface crude oils in western Greece primarily using carbon isotopes and the more microbially resistant tricyclic terpane and aromatic steroid hydrocarbon distributions. All the studied oils seem to fit into three major genetic groups which are consistent with the geologic, tectonic, and geographic settings and are presumably related to different source-rock facies. Group I oils are typical of the abundant oil shows in the Epirus province, northwest Greece. Minor but consistent biomarker differences necessitated subgrouping of the Epirus oils, implying derivation from slightly different sources. Group II oils are located in the Katakolon area, northwestern Peloponnese. Group III oils, which are clearly distinct from the other groups, are centered in Zakynthos Island. An oil seep at Trifos, west central Greece, and a subsurface oil from Paxi Island, because of uncertain correlations, are classed intermediate between Group I and II oils. An aromatic steroid hydrocarbon measurement, modified after Mackenzie et al. (1981), appears useful in determining the relative maturity of biodegraded and conventional oils and carbonate rock extracts.

western Greece↗
USGS1982

Geochemical analysis of potash mine seep oils, collapsed breccia pipe oil shows and selected crude oils, Eddy County, New Mexico

Oil shows, in the form of oil stains and bleeding oil, in core samples from two breccia pipes, Hills A and C, Eddy County, New Mexico, and seepage oils in a potash mine near Hill C breccia pipe are geochemically similar. The geochemical similarities strongly suggest that they belong to the same family of oils and were derived from similar sources. The oils are relatively high in sulfur (0.89 to 1.23 percent), rich in hydrocarbons (average 82 percent), relatively high in saturated hydrocarbon/aromatic hydrocarbon ratios (average 2.9), and based on analysis of seep oils alone, have a low API gravity (average 19.4?). The oils are for the most part severely biodegraded as attested by the loss of n-paraffin molecules. Geochemical comparison of seven crude oils collected in the vicinity of the breccia pipes indicates that the Yates oils are the likely source of the above family of oils. Six barrels of crude oil that were dumped into a potash exploration borehole near Hill C breccia pipe, to release stuck casing, are considered an unlikely source of the breccia pipe and mine seep oils. Volumetric and hydrodynamic constraints make it highly improbable that such a small volume of 'dumped' oil could migrate over distances ranging from about 600 feet to 2.5 miles to the sites of the oil shows.

Open-File Report↗