QUATERNARY CLIMATIC CHANGES INDICATED BY PLANKTONIC-FORAMINIFERA OF NORTHERN INDIAN-OCEAN

The relative abundances of planktonic foraminifera, the changes in the ir coiling and the isotopic record from deep sea cores of some crucial sites in Northern Indian Ocean indicate climatic fluctuations for the past 3.0 million years (Late Pliocene to Pleistocene). The abundance of temperate forms like Globigerina spp. together with sporadic occurr ence of a polar species Neogloboquadrina pachyderma during specific ti me intervals suggest cooling episodes. Warmer intervals are marked by the dominance of tropical assemblages including Globigerinoides spp., Globorotalia s.l., Pulleniatina and Globoquadrina. On the basis of the planktonic foraminiferal frequency changes, four intervals of major c limatic cooling have been recognize-done in the Late Pliocene (2-3 m.y .), three in the Pleistocene immediately above the Pliocene/Pleistocen e boundary (1.6 m.y.), at 0.6 m.y., and during the late Pleistocene. M arked shift in coiling directions within Pulleniatina populations and Globorotalia s.l. is observed to coincide with the frequency changes. There was marked increase of deltaO-18 values in oxygen isotopic recor d of foraminiferal tests around 2-3 m.y. (Late Pliocene) and within th e Pleistocene. Major faunal turnover accompanied by changes in coiling synchronous with the isotopic shifts, suggest these faunal changes to be climatically induced.