Holocene environmental changes as recorded in sediments of a paleodelta, southwest coast of India

Abstract

Sedimentary record of a 40 m deep borehole drilled in a paleodelta region of southwest coast of India has been studied for sedimentary proxies - texture, clay minerals, geotechnical parameters, and pollens. The sedimentary record, spanning from 12 ka to Recent in age, exhibits two different sedimentary environments of deposition. Sediments record high values of moisture content, organic carbon and plasticity index. Sediment texture and geotechnical properties indicate a distinct change in depositional environment from marine to fluvial during the sea level fall i.e., after ∼7 ka. It also suggests that major rise of sea level from ∼11 to ∼7 ka and regression from ∼7 ka to ∼5 ka contributed to the changes in the environment of deposition. The downcore increase of illite and decrease of kaolinite at 12 m depth (∼6 ka), and an upward increase of smectite and kaolinite, and decrease of illite concentration support the major fall in sea level in the region that accounted for the change of depositional environment. The pollen records reveal the abundant occurrence of semi-evergreen type of mangroves during early-to mid- Holocene. Thus, the multi proxy record provides an evidence of change in the environment of deposition from marine to fluvial, which might have been influenced by neotectonics, sea level variations, and monsoonal intensity in the region.