Quaternary Palaeoenvironmental change using Planktic Foraminiferal geochemical and mineral magnetic susceptibility records from the ODP site 758 northern end of Ninetyeast ridge Indian ocean

Abstract

In the present study a deep Sea Drilling project ODP site758 Leg 121 sediment core from the South eastern Indian Ocean has been analysed for understanding Late Middle Pleistocene depositional environment. The sediment core was collected from the 5and#1110192; North latitude at the northern end of the Ninetyeast Ridge. The core details are ODP site 0758 Leg 121 Sector B core 001 H05W1-150 cm. The Ninetyeast Ridge is one of the major submarine ridges in the Indian Ocean. The sediment core analysed is from one of the few ODP sites with well preserved Quaternary sedimentary record, mainly composed of carbonate sediments, foraminifer and terrestrial flux. This thesis deals with the planktic assemblages, geochemical and mineral magnetic susceptibility records which are all proxies for understanding the Quaternary palaeoenvironmental change. The objectives of this present study are to reconstruct the depositional history since the past 100 Ka in the Indian Ocean. Samples at every 2 cm interval were analysed for foraminifera abundance, geochemical concentration and mineral magnetic studies. The time frame of the studied sequence is based on the occurrence of planktic foraminifer faunal datum. In the present study, integration of all the analyses carried out reveals that the sediment core can be broadly divided into six zone (Zone 1 to Zone VI). There an evidence for a decrease in the frequency of fluctuation in magnetite grain size at about 28-24 ka (late MIS 3). There is good correlation between percentage of CaCO3, susceptibility data, S ratio, Mn ppm, Fe ppm and G. ruber planktic form around 82 Ka, 28 Ka and 6 Ka. Increased palaeo wind speeds and volcanic activity during 28-24 ka and increase of coarse grains between 70-82 Ka consequently increased fluxes of terrigenous matter. The main gap that needs to be filled in this study is the applications of stable isotopes of the foraminifera and radiometric dating using 14C, U/Th and Pb isotopes methods that could help in drawing conclusions with age profiles. newline