Mineralogical and geochemical proxies from sediment cores to understand paleoclimate and sea level changes along the southwest coast of India

Abstract

Geochemical variations, among other factors, are attributable to air, water, and land interactions, which are plentiful in the coastal setting. To explore the extent of these interactions in the Vypin Island, southwest of India, three sediment cores were investigated for the mineralogical and geochemical variations. A ∼10 m long core from Kuzhuppilly with a 9 m thick sand deposit suggested a back-barrier ridge condition, largely influenced by fluvial processes. Mineralogy indicated a weakly weathered character, while geochemistry suggested arid conditions, causative of a break in sedimentation at 25–145 cm, 350–365 cm, and 940–955 cm depths with enrichment of Fe, Ti, Zr, and Mn by removal of light-weight Si and Al-rich material. In Chellanam and Munambam cores, characteristic clay and sand layers suggest two varied depositions at the bottom and top, respectively. Saline and oxic depositional conditions under higher sea levels are further complemented by presence of glauconite and kaolinite in bottom clayey sediments, found in the inner shelf depositional setting. The sandy sediments on top are deposited under freshwater conditions (Sr/Ba) but intruded by anoxic conditions indicated by Fe/Al values suggesting a fluvial reworking or deposition. Chemical index of alteration delineate increasing sediment maturity trend from Kuzhuppilly to Chellanam, and Munambam with a depositional hiatus at ∼5.5 m depth in Munambam. Further, glauconite and kaolinite suggest progressive weathering of deeper sediments. This study suggests that clayey sediments were deposited under inner-shelf conditions during higher sea levels, and a trace elemental rich layer between sand and clay proposes further sandy sediment deposition and reworking by dominant fluvial processes during lower Sea levels under semi-arid climate. The work recognizes signatures of three arid phases, regression episodes each and paleo-flood events supported by clay-sand mixed sediment layers.