Neogene planktonic foraminiferal bio-chkonology of dsdp site 219 (chagoslaccadive Ridge), Arabian sea

Abstract

Straiigraphic ranges of planktonic foraminiferal species at close sampling intervals from the Arabian Sea DSDP Site 219 on the Chagos-Laccadive Ridge have allowed the recognition of more than 35 dalums useful for correlation of Neo-gene marine sequences. A detailed qualitative as well as quantitative planktonic foraminiferal analyses from the examined site enabled further to refine the earlier zonal scheme established by Fleisher1. In the present wort, 12 Neogene planktonic foraminiferal zones are recognised based on the First and Last Appearances of selected tax a. Major Neogene epoch boundaries recognised at the site marked by the following species are; Early/Middle Miocene, the first appearance of Praeorbutina glomerosa curva (16,5 Ma); Miocene/Pliocene, the first appearance of Globorotalia tumida tumida (5.2 Ma); Pliocene/Pleistocene, the last appearance of GlobigeriTtoides fistulosus (1.6 Ma). A distinct hiatus covering straiigraphic interval from the upper part of Praeorbuhna gbmerosa Zone to the lower part of Chborotatia praefohsiZone (14 Ma to 16 Ma} is recognised in the early Middle Miocene. It is interesting to note that a similar hiatus at the same stratigraphic intervsal was also identified at other DSDP sites in the Northern Indian and the Southwest Pacific Oceans which corresponds to NH2 hiatus of Barron and Keller2. The widespread deep sea hiatus at the beginning of the Middle Miocene appears to reflect a major paleoceanographic event in response to significant change in the bottom water circulation pattern.