Late Miocene—early Pliocene planktonic foraminiferal biostratigraphy and paleoceanography of low-latitude marine sequences

Abstract

Plate reorganization and development of polar glaciation are closely associated with the changing climatic conditions of the Cenozoic. The planktonic foraminiferal fauna in three low-latitude DSDP sites (224, Ninety East Ridge; 317B, Manihiki Plateau; 366A, Sierra Leone Rise) has been examined to determine how these regions responded to the late Miocene climatic cooling that has been previously observed in high-latitude regions. It has been proposed that an expansion of Antarctic glaciation and a resultant eustatic regression are associated with this cooling, with the latter being at least partially responsible for the Messinian “salinity crisis” in the Mediterranean. Only one of the sites, 366A, shows any significant faunal change during the late Miocene and early Pliocene (approximately 8-3 Ma). During the late Miocene, there is a decrease in the abundance of species considered to be tropical-subtropical, suggesting the incursion of a cool water mass into the Sierra Leone Rise region during this time. The lack of any major faunal changes at Sites 214 and 317B indicates that the water masses of the low-latitude regions of the Indo-Pacific were relatively unaffected by this cooling in the late Miocene. The three sites also show no evidence for a change in the level of the CCD between the late Miocene and early Pliocene; however, this is most likely due to their equatorial position and shallow water depth. Higher-latitude sites from both the Atlantic and the Pacific reveal a definite shoaling of the CCD during the late Miocene.