Population dynamics and palaeoenvironmental inferences of Turonian planktonic foraminiferal assemblages from SE Tanzania and ODP Site 762 (Exmouth Plateau, eastern Indian Ocean)

Abstract

The Tanzania Drilling Program (TDP) recovered hemipelagic sediments from land-based boreholes that yielded extraordinarily well-preserved, diverse Turonian foraminifera. Reliable oxygen and carbon isotopic analyses through most of the Turonian Stage and biostratigraphic data were documented. This study compares Turonian foraminiferal population dynamics and associated geochemical proxy records among the TDP boreholes with correlative records from Ocean Drilling Program Site 762 (Exmouth Plateau, eastern Indian Ocean). The two regions were separated by ∼12° latitude and ∼5000 km of ocean, with the Indian continental plate located between. Taxonomic turnover is similar and is nearly simultaneous in both regions across the transition from the Helvetoglobotruncana helvetica Zone to the Falsotruncana maslakovae Zone (∼93.0 Ma). Changes include overlapping extinctions of all helvetoglobotruncanids, most dicarinellids and one species of Praeglobotruncana and subsequent first appearances of marginotruncanid and falsotruncanid species. Increased abundance of biserial planktonic foraminifera is recorded at multiple TDP sites and at Site 762 across the contact of the Fa. maslakovae and Huberella huberi zones c. 0.5 Myr after the Hv. helvetica / Fa. maslakovae transition. Geochemical records at the two sites do not indicate associated palaeoenvironmental changes in surface water conditions that would explain coordinated changes in species composition on opposites sides of the Indian Ocean.