Changing sedimentary environment during Pleistocene and Holocene in a core from the Eastern continental margin of India

Abstract

Sedimentological and geochemical investigations of the sediments in a core from the eastern continental margin of India, at a water depth of 1200 m, revealed two distinct sediment types. The Late Pleistocene sediments are greyish-black in colour and consist of mud turbidites in the lower part and dolostone breccia in the upper part. They also consist of illite and chlorite-rich clay minerals with high organic carbon and sulfur. Organic matter is of dispersed nature. These are similar to black shales and are apparently formed by rapid burial of terrigenous organic matter by turbidites with intermittent reducing conditions during lowered sealevels. Dolostone fragments appear to have been transported by mass movement processes during the terminal Pleistocene. The Holocene sediments are moderate yellowish-brown in colour and with detrital viviaoite nodules at the base. These sediments are clayey with mont-morillonite-rich, illite-poor clay minerals, lower organic carbon and sulfur contents and ferruginised pyrite grains, deposited under oxidising conditions. The marked changes in the sedimentary environments are attributed to climate and sealevel changes during Pleistocene and Holocene.