Pleistocene sea-level and environmental changes during glacial-interglacial cycles recorded in beach ridges of the Thai-Malay Peninsula

Abstract

Beach ridges are relict coastal landforms with subsurface deposits that can be used to reconstruct past sea-level and environmental changes. Nonetheless, beach ridges, especially those formed during the Pleistocene, can be easily modified by post-depositional processes triggered by various climatic events during glacial-interglacial cycles. Therefore, detailed investigations are necessary to utilize beach ridges as records of past sea level and environmental conditions. This study employs a multidisciplinary approach, including ground-penetrating radar (GPR) surveys, sedimentological analysis, and luminescence dating, to determine the evolution of beach ridges in the Thai-Malay Peninsula. Based on GPR and sedimentological data, evidence of beach progradation is identified, indicating that the deposition of coarse-grained beach ridges occurred on the beach face where sediments accumulated in a high-energy depositional environment. These beach face deposits are subsequently covered by thick layers of aeolian deposits that were likely reworked at the surface of the beach ridges. Luminescence dating reveals that the deposition of the oldest beach ridges occurred prior to 190 ka, during the interglacial period of the Marine Isotope Stage (MIS) 7. Subsequently, the beach ridges were modified by aeolian reworking episodically until the end of the Pleistocene during times when the sea level was low, resulting in a vertical build-up. The presence of aeolian deposits supports the concept of climate aridification and reduced vegetation cover in Sundaland during that time.