Origin of Buckhorn Asphalt, Deese Group (Pennsylvanian), Central Arbuckle Mountains, Oklahoma
James L. Sadd, Neil Peterson, Christopher G. St. C. Kendall
Asphalt-impregnated sediments of the Pennsylvanian Deese Group (Buckhorn asphalt), in the Mill Creek syncline asphalt district, share many similarities with the nearby tar-sand bitumens of the Ordovician Oil Creek Formation. Both originated as oils emplaced during Middle to Late Pennsylvanian orogenesis (Arbuckle event) when the two formations were juxtaposed by combined wrench and dip-slip faulting. Sterane patterns indicate that the two oils were generated from similar source rocks, both rich in terrestrial plant organic matter; terpane patterns suggest source rock deposition in marine deltaic to shallow-shelf conditions. Both oils were subjected to varying degrees of biodegradation and formation water washing. Saturate and aromatic fractions were removed more completel than the NSO fraction; asphaltenes were generated and/or added during alteration. Certain biomarker terpanes (e.g., C27 hopane, gammacerane) were more resistant to biodegradation than previously reported. Deese asphalts differ from the Oil Creek bitumens in important ways. They are two to three times richer in asphaltenes (to 78%) and show considerable variation in sterane alteration at a given level of saturates and aromatics depletion, suggesting that formation water washing was more important to Deese alteration. Formation of some of the asphaltene-rich asphalts may have been accompanied by gas deasphalting of the parent oil resulting in asphaltene precipitation within the Deese section. This hypothesis is favored by the abundance of mature Type III (woody, herbaceous) ker gen in the asphaltic section and by physical evidence of overpressuring during petroleum emplacement, including concordant seams of asphaltite and of passively precipitated calcite (calcite beef).
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.