Late Quaternary Evolution of Songkhla Coast, Southern Thailand, Revealed by OSL Dating

Abstract

Coastal sediments in Songkhla Province (Southern Thailand) provide information on paleoenvironmental conditions; however, there is no geochronological data available for this area. This pilot study checks the suitability of optically-stimulated luminescence (OSL) dating to understand the geological evolution of the beach since the late Pleistocene. The single aliquot regenerative (SAR) dose technique of coarse grain quartz provided numerical ages from 160 ka to 4 ka. The oldest sample showed evidence of weathering, leading to an age overestimation due to leaching of radioelements. The overestimated age has been corrected based on a time dependent dose rate model. OSL ages provide a geochronological framework to interpret the geological and geomorphological evolution of the area since the last interglacial when the sea level was 5 m above present day sea level. Windblown sand overlying last interglacial deposits gave depositional ages of ca. 100, 58 and 17 ka. Moreover, during the period 34-38 ka ago, lacustrine and fluvial environments were prevalent, as deduced from sediment characteristics and sea level history. The OSL chronology established for windblown, lacustrine and fluvial deposits in Songkhla indicates the fluctuation of dry and humid climates during the last glacial period in Songkhla. Until the mid-Holocene, after the sea level had rapidly transgressed, a lagoon had been formed at around 1,100 m from the present coastline, supported by an OSL age of 6.8 ka. In the period 6.8-5.7 ka ago, the sea level reached its highstand and then regressed, resulting in two dunes deposited between 4 and 6 ka ago.