Neogene benthic foraminifers: distribution in depth traverse, southwest Pacific.

Abstract

Early Miocene to Quaternary benthic foraminifers have been quantitatively studied (>63 mu m size fraction) in a southwest Pacific traverse of DSDP sites at depths from about 1300 to 3200 m down the Lord Howe Rise. Dominant species include Epistominella exigua, E. rotunda and Globocassidulina subglobosa, which prevail in the three sites, and Oridorsalis umbonatus, E. umbonifera, and Cassidulina carinata, which occur usually in frequencies of between 10 and 30%. Faunal changes in Neogene benthic foraminiferal assemblages are not similar in each of the three sites, but faunal successions are most similar between the two shallowest sites. The deepest site differs in composition and distribution of dominant species. There are three intervals during which the most important changes occur in benthic foraminiferal assemblages: the early middle Miocene (14 Ma); the late Miocene (6 Ma); and near the Pliocene/Pleistocene boundary at about 2 Ma. These major faunal changes are all associated with known major paleoceanographic events - the middle Miocene development of the Antarctic ice sheet; the latest Miocene global cooling and increased polar glaciation; and the onset of quasiperiodic glaciation of the Northern Hemisphere. These major paleoceanographic events undoubtedly had a profound effect on the intermediate and deep water mass structure of the Tasman Sea as recorded by changes in benthic foraminiferal assemblages. -from Authors