Plio-Pleistocene Planktic Foraminiferal Biochronology of ODP Site 762B, Exmouth Plateau, Southeast Indian Ocean

Abstract

The Indonesian Throughflow region connects the tropical Pacific Ocean with the eastern Indian Ocean, and variability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magnetochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understanding of the coupled histories of the El Niño Southern Oscillation, Western Pacific Warm Pool, Indonesian Throughflow, and the eastern Indian Ocean has greatly benefitted from the chronological framework provided by planktic foraminiferal biostratigraphies from these regions. Ocean Drilling Program (ODP) Hole 762 lies under the influence of the Leeuwin Current, originating from the Indonesian Throughflow. Multiproxy data have been collected from Hole 762B and other nearby sites for paleoceanographic interpretation. However, a detailed planktic foraminiferal biostratigraphy integrated with magnetochronology is not available from this site. We provide here the sequential order of planktic foraminiferal First Occurrence (FO) and Last Occurrence (LO) events, which allowed us to divide the examined section into seven biostratigraphic zones. The biostratigraphy was integrated with magnetostratigraphy using revised ages of magnetochrons, which yielded biochronological age estimates for planktic foraminiferal events. A major planktonic faunal turnover between 3.4 and 2.7 Ma is probably related to the onset of the Northern Hemisphere glaciation and related changes in the Indonesian Throughflow. We have compared our numerical age estimates with published ages from other parts of the world. The diachronism observed probably is related to the local oceanographic setting of ODP Hole 762B, which has been alternatively influenced by changing strengths of the warm Leeuwin Current and the cold west Australian Current. The biochronology established here will be useful for correlating paleoceanographic events in the region.