Sediment Characteristics and Depositional Environment of Silica Sand Deposits of the East Coast, Tamil Nadu

Silica sand deposits are exposed along the East Coast, Tamil Nadu, nearly 80 km south of Chennai. The original sediment is quartz sand to feldspathic quartz sand Soil has developed over the younger deposits. Trough cross bedding is well developed in the younger sediments. Textural analyses of silica sand were carried out for compatative study.

Silica sand varies from very coarse sand (-0.25φ to 0.5φ), medium sand (1.25φ to 2φ) fine sand (2.25φ to 3φ), very fine sand (3.25φ to 4φ) and coarse silt (4.06φ to 5φ). Fine to medium sized grains are dominant in the silica sand. The silica sand is poorly sorted, fine skewed, leptokurtic to platykurtic in characteiistics. Beach and dune sediments are predominandy coarse sand with heavy minerals. The dune sediments are moderately to well sorted, fine skewed, and leptokurtic. The beach sediments are well sorted strongly coarse skewed, and platy to leptokurtic. The sphericity and roundness values of the silica sands vary from rounded to sub rounded and are very equant. The various types of surface features are 'V shaped notches, conchoidal fractures and striations The study shows that the depositional environment of silica sand is markedly different from the aeolian and beach enviionment Bivariant plots and textural analyses of the silica sands indicate that they have been primarily deposited by fiuvial action.