Textural Variation and Depositional Environments of Innershelf Sediments, off Kalpakkam, Southeast Coast of India

Surface sediment samples collected from 42 locations up to a water depth of 53 m during pre-NE monsoon (September, 1 995) and post-NE monsoon (April, 1996) seasons in the innershelf region, off Kalpakkam, were analysed for textural parameters, calcium carbonate and organic matter. Grain size distribution shows that the innershelf is carpeted with a mosaic of sand and silty sand with minor amounts of clay (0-4%). The analysed sediments are characteristically very poorly and poorly sorted, and dominantly positively skewed with very leptokurtic and very platykurtic nature. The occurrence of relict sediments in the form of coarse sand deposit around 19th km from the present shoreline has been identified as a palaeoshoreline. Bivariate plots of grain size parameters reveal that the sedimentary depositional environment is influenced dominantly by river/dune/beach conditions. A linear patch of coarse sand with higher concentration of CaC03 (>15%) and very low organic matter (<0.4%) at a depth around 50-53 m confirms the existence of the palaeoshoreline, formed probably during Holocene low sea level. SEM photomicrographs also support the occurrence of energy enviroment related to shoreline.