Neogene planktonic foraminifers from Sites 761 and 762 off northwest Australia

Abstract

Diverse, warm-water planktonic foraminiferal faunas prevailed on the Wombat and Exmouth plateaus during the Neogene. Invasions of cool-water species occurred during periods of global cooling in the late middle Miocene, late Miocene, and Pleistocene, and reflect periods of increased northward transport of cool surface water, probably via the West Australian Current. The sedimentary record of the Neogene on Wombat and Exmouth Plateau is interrupted by two hiatuses (lower Miocene, Zone N5, and upper middle to upper Miocene, Zones N15-N17), and one redeposited section of upper Miocene to uppermost Pliocene sediments. Mechanical erosion or nondeposition by increased deep-water flow or tilting and uplift of Wombat and Exmouth plateaus, resulting in sediment shedding, are the most likely explanations for these Miocene hiatuses. The redeposited section of upper Miocene to uppermost Pliocene sediments in Hole 761B, certainly reflects a latest Pliocene period of uplift and tilting of the Wombat Plateau. An important finding was the occurrence of Zone N15-correlative sediments in Hole 762B without any representative of Neogloboquadrina. It is suggested that Neogloboquadrina acostaensis evolved from Neogloboquadrina atlantica in the North Atlantic within Zone NN9, but how and where in the region this speciation took place is still uncertain. -from Author