Cretaceous southern high latitude benthic foraminiferal assemblages during OAE 2 at IODP Site U1516, Mentelle Basin, Indian Ocean

Abstract

At Site U1516 (Mentelle Basin, southeast Indian Ocean, offshore western Australia), the International Ocean Discovery Program (IODP) Expedition 369 recovered an almost complete pelagic record of the Upper Cretaceous, including the Oceanic Anoxic Event 2 (OAE 2). To better understand paleoenvironmental changes across OAE 2, 32 samples were analysed for benthic foraminiferal abundance data that represent one of the few benthic foraminiferal datasets spanning the OAE 2 in the southern high latitudes.The OAE 2 interval at Site U1516 is characterized by an interval of low CaCO3 content that contains a prominent positive Carbon Isotope Excursion (CIE). The record of the OAE 2 can be subdivided in pre OAE 2, pre max-CIE, low CaCO3, and post low CaCO3 intervals. Through the Cenomanian–Turonian boundary, we document an extreme decline in benthic foraminifera during OAE 2, that is followed by a profound repopulation event in the post low CaCO3 interval.Benthic foraminiferal assemblages indicate an outer neritic to upper bathyal depositional environment. During the pre OAE 2 and pre max-CIE intervals, calcareous deep-water gavelinellids, lingulogavelinellids and gyroidinids are dominant. In the low-carbonate interval, the microfossil record documents a substantial increase in radiolaria and foraminifera are almost absent as only three out of nine samples contain benthic foraminifera. Changes in benthic foraminiferal assemblage composition are documented in the initial low CaCO3 interval, underlying the maximum CIE and associated interferences. Comparison of the pre- and post-CIE benthic foraminiferal assemblages highlights a distinct repopulation event during the post max- CIE interval mainly represented by the conspicuous increase in abundance of agglutinated taxa and Conorboides. Compared to other southern high latitude records, the dataset collected at Site U1516 represents one of the most complete benthic foraminiferal records across the OAE 2 that registers the Late Cretaceous environmental changes in the Southern Hemisphere.