Grain Size Analysis for Elucidation of Depositional Environment of Kalpakkam, India

Abstract

To assess the textural variations and to elucidate the depositional processes along Kalpakkam-Mahabaliuram stretch, beach and seabed sediments were collected seasonally in 2010, i.e., January (Post-monsoon), May (Summer), August (Southwest monsoon) and October (Northeast monsoon). The samples were collected in a transect pattern viz. from beach, 200 m, 500 m and 1000 m into the sea from 12 stations, stretching from Sadras in the south to Mahabalipuram in the north, covering a coastal length of about 15 km. For textural characterization, the sediment samples were subjected to sieve analysis. Granulometrically, the sediments are coarse to fine grained, moderately to moderately well sorted, exhibiting positive and negative skewness. The shore normal variations in mean size show reduction in coarseness towards the sea. The apparent closeness in the mean of grain size statistics between beach and seabed is partly due to similarity in sediment source (eroding coastal plain) as well as the similarity in depositional processes. Kurtosis of beach and seabed sediment varies between very platykurtic to very leptokurtic implying that sediments, to an extent, have attained sorting in a high energy environment. For elucidation of depositional environment, sub-population analysis, bivariant plots (i.e., mean vs standard deviation, skewness vs mean, skewness vs standard deviation, skewness vs kurtosis, and kurtosis vs mean), and discriminant function analysis were carried out. The sediments along Kalpakkam-Mahabalipuram stretch reveal the dominance of beach and beach related processes, and influence of fluvial processes during deposition.