APTIAN-ALBIAN PLANKTIC FORAMINIFERA FROM DSDP SITE 364 (OFFSHORE ANGOLA): BIOSTRATIGRAPHY, PALEOECOLOGY, AND PALEOCEANOGRAPHIC SIGNIFICANCE

Abstract

This work presents a taxonomic, biostratigraphic and paleoecological study of planktic foraminifera recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Twenty-nine planktic foraminiferal species were identified, enabling the identification of late Aptian–late Albian biozones, from the Hedbergella trocoidea Zone to the Pseudothalmanninella ticinensis Zone. A major unconformity from the latest early–earliest late Albian was identified in core 31, with the Microhedbergella rischi Zone in direct contact with the Pseudothalmanninella ticinensis Zone. The recovered assemblages are characterized by open marine epipelagic dwellers and indicate predominant mesotrophic environmental conditions throughout the studied stratigraphic succession. Aptian planktic foraminiferal assemblages have a tropical/subtropical paleobiogeographic affinity, supporting a surface-water connection between the central proto-Atlantic Ocean and the northern South Atlantic Ocean (north of the Walvis Ridge-Rio Grande Rise) by the late Aptian. Trends in isotopic values for δ 13 C suggest a late Aptian age ( Globigerinelloides algerianus Zone) for the stratigraphic interval from core 42 to ~core 37, where age-diagnostic foraminiferal species are missing. Black shale levels in cores 42–39 are probably the local expression of the “late Aptian anoxic event.”