Cretaceous calcareous nannoplankton biostratigraphy, sedimentation history, and paleoceanography of western North Atlantic Ocean

Abstract

Integration of biostratigraphy and sedimentology of Deep Sea Drilling Project (DSDP) drill core samples from the western North Atlantic Ocean resulted in a reconstruction of the Cretaceous geologic history of this ocean basin. Comparison with COST well data from the eastern United States continental shelf allowed for a comparison of sedimentary events which occurred during the Cretaceous in both continental margin and deep ocean locales. Variation in organic carbon content, CaCO3 content, grain size (all taken from DSDP reports), and sedimentary structures were used to characterize the sediments and, therefore, the sedimentary process. These sedimentologic factors and certain paleoclimatic indicators (e.g.: paleotemperature data; latitudinal distribution of coal and evaporates) were used to assess the paleoceanography of the Cretaceous. The Cretaceous sedimentary history of the wester North Atlantic Ocean was subdivided into five separate events. During the Neocomian, millimeter-scale laminated to bioturbated limestones were deposited in the deep basin. A shelf-fringing reef was present along portions of the eastern coast of the United States. Carbonates were deposited in the Blake Plateau-Georgia Embayment area, whereas clastics were deposited from the Baltimore Canyon to the Flemish Cap. A series of dark-colored, organic carbon-rich clays were deposited in the deep basin during the mid-Cretaceous. These black clays are indicative of anoxic condition. The black clays are characterized by terrestrially-derived organic carbon, calculated sedimentation rates which indicate pelagic sedimentation, and by 'hemipelagic' calcareous nannoplankton. These components of the black clays suggest a seasonal input of terrigenous-derived material through delta systems which prograded across the continental shelf during the mid-Cretaceous. Variegated clays (Albaian to Cenomanian) succeeded the black clay interval and are indicative of oxygenated conditions.