Planktic Foraminiferal Species Turnover Across Deep-Sea Aptian/ Albian Boundary Sections

A major planktic foraminiferal species turnover accompa-nied by a dramatic reduction in shell size, a fundamental change in shell architecture, and a precipitous drop in the abundance of planktic relative to benthic species occurs across the Aptian/Albian boundary interval (AABI) at globally distributed deep-sea sections. Extinction of the large and distinctive planktic foraminifer Paraticinella eube-jaouaensis, used to denote a level at or near the Aptian/ Albian boundary, coincides with the extinctions of relatively long-ranging Aptian species of Hedbergella and Globiger-inelloides. At Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic), which is the most complete and best preserved of the studied AABI sections, the Aptian assemblage is of low diversity and species are replaced by