PALMER, SUSAN E., Amoco Production Company, Tulsa, OK
ABSTRACT: Organic Geochemistry of Organic-Rich Cretaceous Carbonates with Regard to Depositional Setting
Organic-rich carbonates of Albian to Campanian in age have been characterized with regard to kerogen composition, depositional setting, and biological marker distributions. Samples include Campanian inner shelf dolomitic limestones, Croatia; Campanian outer shelf limestones and siliceous limestones of the Sudr "Brown Limestone," Gulf of Suez; middle to outer shelf limestones of the Cenomanian Bahloul Formation, Tunisia; and forereef basin limestones and siliceous limestones of the Albian-Cenomanian Tamaulipas Formation, Mexico. Common features among all of these carbonate units include low to moderate amounts of rearranged relative to normal steranes and the presence of 30-norhopanes. Benzohopanes are present on all samples but are unusually abundant in the Croatia Campanian inner she f deposits, even when their low maturity is considered. Kerogen ranges from high-sulfur Type I-II for samples from Croatia to moderate-sulfur Type I-II kerogen in the "Brown Limestone," and Type II to I-II low-sulfur kerogen in the Bahloul Formation. Gammacerane is prominent in the siliceous limestone facies of the "Brown Limestone;" this facies was deposited under very low oxygen conditions. Influx of detrital material i6 recorded in the isotopic composition and biomarker distributions of the Bahloul samples. However, the occurrence of 28, 30-bisnorhopane, a compound ascribed to organic matter deposited in association with upwelling, has not been correlated to environmental conditions or organic input. Based on a limited set of samples, the Tamaulipas Formation is characterized by high 29 relative to C27 steranes, presence of 30-norhopanes and benzohopanes.
AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.