Textural Characteristics of the Visakhapatnam Shelf Sediments

Textural parameters, viz., mean, standard deviation, skewness and kurtosis and CM patterns in respect of 150 offshore sediments from the continental shelf off Visakhapatnam enabled delineation of two distinct sedimentary facies, one in the northern sector (Visakhapatnam - Bheemunipatnam) and the other in the southern sector (Visakbapatnam - Pudimadaka). The sedimentary facies in northern sector includes sands (from coast up to 37 m) followed offshore by silty sands (up to 50 m), sandy silt (up to 70 m) and silts (up to 80 m) and that in the southern sector, sands (up to 30 m), silty sands (between 30 - 40m and 50 - 80 m) followed offshore by sandy silts (between 40 - 50 m). There is a progressive seaward fining of sediments in the southern sector, whereas in the northern sector the fining is towards both sea and land. Fining of sediments with depth, a feature common to open shelves, is attributed to wave action. Distribution of medium sand zone in the northern sector between 15 to 40 m along the coast has been considered to be the result of dumping of dredged out material from the nearby port area. A major part of the study area is floored by poorly-sorted sediments. Skewness values of the sediments in the southern sector increase uniformly with depth whereas they show more complex pattern in the northern sector. Leptokurtic sediments bordering the coast in the northern sector indicate removal of fines through wave and current activity. CM diagram indicates the prevalence of low to moderate current activity in the south and highly turbulent zones in the north.