Abstract: Vembanad lagoon is the largest backwater system on the Kerala coast and acts as a major center for quaternary deposits. Peat deposits have been identified at different depths in the boreholes between sandy clay and clayey sand sedimentary faces. These peat deposits gave radiocarbon age of 40,000yrs BP. Pollen analysis of peat revealed the existence of mangrove vegetation and evergreen forest, suggesting humid climate during that time. Presence of desiccated clays beneath the peat deposits suggests arid climate prior to the humid climate during 40.000yrs BP.