Journal of Foraminiferal Research, v. 52, no. 4, p. 248–263, October 2022 PLIO-PLEISTOCENE PLANKTIC FORAMINIFERAL BIOCHRONOLOGY OF ODP SITE 762B, EXMOUTH PLATEAU, SOUTHEAST INDIAN OCEAN Ashutosh K. Singh* and Devesh K. Sinha Department of Geology, Centre of Advanced Studies, University of Delhi, Delhi-110007, India ABSTRACT The Indonesian Throughflow region connects the tropi- cal Pacific Ocean with the eastern Indian Ocean, and vari- ability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magne- tochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understand- ing of the coupled histories of the El Niño Southern Oscil- lation, 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 Cur- rent, originating from the Indonesian Throughflow. Multi- proxy 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 pro- vide 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 bios- tratigraphic 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 be- tween 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 numeri- cal age estimates with published ages from other parts of the world. The diachronism observed probably is related to the lo- cal 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. INTRODUCTION Precise age determination of oceanic sediments and their regional and global stratigraphic correlation is a necessary prerequisite for paleoceanographic and paleoclimatic recon- struction. One of the most dependable methods of precise age determination of the oceanic sediments is to establish reliable planktic foraminiferal biostratigraphies integrated with magnetostratigraphy from the world’s oceans. Such an integrated approach has greatly facilitated spatiotempo- ral correlation of the paleoceanographic and paleoclimatic *Correspondence author. Email: ashutoshsingh@geology.du.ac.in events and thus understanding their cause-and-effect rela- tionships. For example, understanding the coupled histo- ries of the El Niño-Southern Oscillation (ENSO), West- ern Pacific Warm Pool (WPWP), Indonesian Throughflow (ITF), and the Eastern Indian Ocean (EIO) has greatly ben- efitted from the precise chronological framework provided by planktic foraminiferal biostratigraphies from these re- gions [e.g., Sinha & Singh, 2008 (Eastern Indian Ocean); Srinivasan & Sinha, 1992; Chaisson, 1995; Kaushik et al., 2020 (Western Pacific Warm Pool); Groeneveld et al., 2021 (Indonesian Throughflow region)]. Recent years have witnessed enormous interest in un- derstanding paleoceanographic and paleoclimatic events in the EIO due to its linkage to the tropical Pacific via the ITF and its response to changes in ENSO (Kuhnt et al., 2004; Sinha et al., 2006, Sinha & Singh, 2007, Karas et al., 2009, 2011; Christensen et al., 2017; Andrae et al., 2018; De Vleeschouwer et al., 2018; Stuut et al., 2019; Auer et al., 2019, 2020). The ITF is a significant part of the up- per returning arm of the global ocean conveyor belt con- necting the tropical Pacific with the EIO (Fig. 1). Kuhnt et al. (2004) provided a detailed account of the Neogene history of the ITF and described it as a major tropi- cal “switchboard” in the global thermohaline circulation affecting the tropical climate dynamics on various time scales. Srinivasan & Sinha (1998, 2000) suggested that the Indonesian Seaway closed in the Early Pliocene, restrict- ing the passage of deep and thermocline waters from the Western Pacific to the Indian Ocean, based on planktic foraminiferal biostratigraphic and paleobiogeographic dif- ferences between Deep Sea Drilling Project (DSDP) Sites from the Northern Indian Ocean (Site 214) and the tropi- cal Pacific (Site 846B). Their interpretation was based on the absence of the Early Pliocene thermocline dwelling planktic foraminiferal species Pulleniatina spectabilis from the trop- ical Indian Ocean while it was present in sediments of the same age in the western equatorial and other tropical Pacific DSDP sites. Groeneveld et al. (2021) also noted the absence of Pulleniatina spectabilis at International Ocean Discovery Program (IODP) Site 1463 (18°59 ′ S, 117°37 ′ E, Expedition 356) near ODP Hole 762B in the Indonesian Throughflow region and suggested the existence of a biogeographic bar- rier for the deeper water in the Indonesian region in the Early Pliocene. Wei (1998) noted an increase in warm-water planktic foraminiferal species at DSDP Site 590 in the Southwest Pacific and attributed this to a southward shift of the Tas- man Front in the Early Pliocene caused by a probable tec- tonic closure of the New Guinea Seaway due to north- ward movement of Australia. This northward movement also resulted in a change in the source water of the In- donesian Throughflow from the warm South Pacific to the 248 Downloaded from http://pubs.geoscienceworld.org/cushmanfoundation/jfr/article-pdf/52/4/248/5731120/i1943-264x-52-4-248.pdf by University of Delhi user on 01 November 2022