Abstract: Newly Recognized Petroleum Source-Rock Units in East-Central Utah--Implications for Detection of Petroleum in Nonmarine Units

Thomas D. Fouch, George E. Claypool, John H. Hanley, Robert H. Tschudy

Many important source-rock units that are difficult to detect commonly are grouped with facies generally not considered to contain petroleum source beds. In Price River Canyon, rocks of the North Horn Formation include attrital coal of subbituminous rank intercalated with organic-rich laminated ostracod, charophyte, and mollusk-lime wackestone. The coal yields as much as 83 gal of oil per ton (346 1/MT). Cumulative thickness of the coal is about 3 ft (1 m), and the sequence can be traced southeast on outcrop for more than 4 mi (6.5 km) to an erosional edge. Analysis of representative samples indicates that the most abundant compound within the heavy (C₁₅) saturated hydrocarbon fraction is pristane and that the ratio of pristane to phytane is very high (6.7 to 9 0). Odd carbon numbers of n-paraffins greatly predominate over even carbon numbers (CPI = 1.9 to 1.5). These characteristics indicate the presence of organic matter derived from land plants. The coals contain palynomorphs and mollusks that indicate formation during the late Paleocene in a fresh, clear quiet-water environment that included aquatic vegetation. Petroleum source-rock coals also are present in the basal part of the main body of the Green River Formation at Willow Creek Canyon and near Soldier Summit. Similar depositional settings are present in much of the Great Basin and in the Rocky Mountains. Sedimentary structures, rock type, and mollusk, charophyte, and palynomorph content of the associated units can be characterized and used to predict the presence and distribution of other organic-rich beds in strata not previously considered to contain petroleum source rocks.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC