Sources and deposition of organic matter in Cretaceous passive margin deep-sea sediments: a synthesis of organic geochemical studies from Deep Sea Drilling Project Site 603, outer Hatteras Rise

摘要

The results of organic geochemical studies of rock samples from Cretaceous strata at Site 603 on the outer Hatteras Rise are reviewed and integrated with their lithostratigraphic information. Although most of the strata contain little organic carbon, black shales enriched in organic matter were found in two settings. 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, except during the Cenomanian-Turonian, when the entire Atlantic Ocean may have briefly become anoxic. Organic matter in the sediments from all locations is thermally immature.