Miocene Benthic foraminifera and paleoceanography of dsdp sites along ninety East ridge, Northern Indian ocean

Abstract

The present paper dealing with the integrated quantitative and isotopic analyses of benthic foraminifera is an attempt to infer bottom water paleoceanographic changes in the Northern Indian Ocean DSDP sites 214 and 216 and their impact on global climates during the Miocene. The taxa showing significant changes have been used which are represented by Neoi/uigerina probostidea, Neouw'gerina ampullacea, Cibicides kulknbergi, Chiades wuelkrstorji, Ghbocassiddma padfica, Giobocassidulina subglobosa, Mmna fl/astriensis and Oridowte umbonatus. The Oligocene/Miocene boundary transition in the Northern Indian Ocean appears to represent an interval of cool bottom waters which is marked by increased Giobocossitfulino and decreased Cibidides abundances, This event is followed by warming of bottom waters in late Early Miocene representing the climax of Neogene warmth. In general, the Early Miocene bottom water conditions in the Northern Indian Ocean were warm punctuated by four intervals of frigid bottom water conditions. Middle Miocene assemblages are characterized by higher abundances of Globvcassidulm pacifica reflecting a cooling event probably in response to increased growth of Antarctic ice sheets. This is supported by oxygen isotope record of benthic foraminifera characterized by rapid excursion of δ¹⁸O towards higher values during c. 16.5 to 13.5 Ma. This excursion has been attributed to high latitude cooling and permanent accumulation of East Antarctic, ice sheets. The Late Miocene assemblages are dominated by Bulimira nlazarfensjs and species of Uuigerina showing remarkable frequency changes. The sudden and increased abundance of LMgeHna between c 8.0 and 7.5 Ma at Site 214 reflects a major increase in Antarctic ice sheet volume andits influence in the deep waters of the Northern Indian Ocean, This event also coincides with the West Antarctic ice sheet formation. The coincidence of Chron-6 negative carbon shifi at about 6.2 Ma with higher (Angeriha percentages reflect global climatic cooling and the resultant major regressive-cycle-in the Late Miocene. The Terminal Miocene Event (about 5.7 to 5.2 Ma) is characterized by highest Uuigerino percentages of the Miocene suggesting strong influence of AABW towards Northern Indian Ocean as a result of permanent build up of Antarctic ice sheets and intensified Atmospheric - Oceanic circulation.