Seasonal Variation in Textural Characteristics and Sedimentary Environments of Beach Sediments, Karnataka Coast, India

Abstract

Seasonal (post- and pre-monsoon) changes in texture and environment of deposition of beach sediments of Karnataka coast have been studied using various statistical parameters (Mean size, Standard deviation, Skewness and Kurtosis). These parameters were obtained for all the sieved sediment samples (68 for each season), using GradistatV8.0 and G-Stat software packages. Based on the range of variability of these statistical parameters, the studied coast has been divided into four sectors. Sector I extends from Talapady to Surathkal; sector II includes beaches from Mukka to Kota. Sector III comprises Marvanthe and Nesther beaches and those lying between Murdeshwara and Devbagh fall in sector IV.Passega's CM and Tractive current diagrams were prepared to understand the energy condition of depositional currents and mode of transportation of sediment respectively. Linear Discriminant Function (LDF) plots were used to understand the environment of deposition of sediments. TheCM diagram reveals predominance of beach and tractive currentconditions along the entire coast. The Tractive current diagram indicates that deposition of sediment takes place by rolling and bottom suspension during post-monsoon, whereas by graded suspension and no rolling conditions during pre-monsoon season in sector I. In sector II, deposition of sediment takes place by bottom suspension and rolling during both the seasons. In sector III, the sediments show change in energy conditions with time where they are deposited by rolling during post-monsoon, whereas prevailing of low energy condition during pre-monsoon season as deposition of sediment takes place by bottom suspension and rolling. In sector IV, bottom and graded suspensions have been the dominant mode of deposition during both the seasons. The LDF analysis of sediment samples indicates dominance of shallow marine environment of deposition for both the seasons. The LDF plotsreveal that sector I predominantly belongs to beach shallow to beach littoral environment for both the seasons. Shallow marine agitated environment of deposition was observed for the post-monsoon season in sector II, while increase in energy conditions at this sector led tobeach shallow environment of deposition during the pre-monsoon season. Sector III shows predominance of beach littoral environment of deposition for the post-monsoon, while beach shallow environment of deposition during the pre-monsoon indicating decrease in energy conditions. Sector IV plots show little or no change for both the seasons and the samples predominantly fall in shallow marine agitated environment of deposition.