Sediment - size distribution of innershelf off Gopalpur, Orissa coast using EOF analysis

Abstract

Earlier studies on grain-size analysis of sediment samples collected over the innershelf of Gopalpur coast have revealed two significant depositional environments viz beach and dune. Sediment samples from water depth of < 15 m show the representation of dune type of environment and the samples beyond 15 m in the study area are characterised of beach type of environment suggesting submergence of two physiographic units of beach and dune due to Holocene transgression. Empirical Orthogonal Function (EOF) analysis carried out for the above units on grain-size distribution of the sediments in the ø - size class revealed that the first three ø - dependant eigen function viz. c1, (ø), c2 (ø) and c3 (ø) account for more than 95% of variance predominantly represented by the first - dependent function c1 (ø) alone. This first function c1 (ø) of deeper sediments (15 - 30 m depth) contribute 76.34 % of the total distribution representing coarser sands, in general, and characterized by predominance of very coarse sand to the extent of 40%. Shallow sediments ( 0 - 15 m depth) contribute 70% of the distribution—representing medium to fine sand with the dominance of 40% of fine sand. This eigen function c1 (ø) showed significant differences in the concentration of grain size particles across the innershelf reflecting the change in the energy condition that prevailed in the area during the emergence of the innershelf.