Nature of sub-surface sediments off Ambalapuzha, Kerala: Implications on sea level change and mudbank formation

Abstract

Sub-seabed sediments off Ambalapuzha consist of a lower marshy sequence followed by transgressive sand sheet and topped by shelf mud deposit. Lower unit of interbedded, compact, silty clay and sand is characterised by carbonaceous content and iron stained quartz grains denoting regression. Coarse sand build-up within the medium grained sand at about -12 m depth suggest a stillstand surf zone deposit and indicate an interruption in the Holocene transgression. Shelf mud thins out seaward over the transgressive sands. The shelf mud is temporally related to the mudbank phenomenon and the thickness of the mud blanket, a pointer to the antiquity of the phenomenon.