Synthesis of Organic Geochemical Studies, Deep Sea Drilling Project Leg 93, North American Continental Margin

Abstract

The results of organic geochemical studies of samples from Site 603 on the outer Hatteras Rise and from Sites 604 and 605 on the New Jersey continental slope are reviewed and integrated with lithostratigraphic information from those locations. Although most of the sediments and rocks encountered at all three sites contain little organic carbon, "black shales" enriched in organic matter were found in Cretaceous strata obtained from Hole 603B. These rocks exist as claystones in the Aptian to Turonian Hatteras Formation and as marlstones in the Neocomian Blake-Bahama Formation. Terrigenous organic matter predominates in these deposits, except in Cenomanian and Valanginian rocks, where marine material becomes dominant. Organic carbon concentrations in Cenomanian black claystones are higher than any previously reported from the western North Atlantic, but lower than the concentrations found in the eastern North Atlantic. Black shales at Site 603 appear to result from downslope transport and rapid reburial of coastal and ocean margin sediments by turbidity flows. Deep-basin anoxia is not a major factor. At Site 605, a well-defined Cretaceous/Tertiary boundary was obtained, and terrigenous components of the organic matter diminished in sediments deposited above this boundary. Organic matter in the sediments from all locations is thermally immature.