Quaternary coastal morphology and deposition in Thailand

Abstract

Abstract Thailand is part of the Asian continent that is generally considered to be tectonically stable compared to adjacent regions in southeastern Asia. However, studies of Quaternary stratigraphic sequences, depositional processes and coastal morphology of the Thailand coast, have provided evidence of continuing Cenozoic epeirogenic movement influencing coastal evolution. These movements have affected coastal and river depositional responses to climate and eustatic sea level change. The Quaternary marine formations are extensive along the coastal zone for a distance of about 1850 km in the Gulf of Thailand and occur sporadically along the 865 km west coast of the Thai Peninsula. On the Thai Peninsula, the emergence of the west coast has resulted in the formation of numerous islands, drowned valleys, short and narrow beaches and truncated headlands, in the high energy coastal erosion regime of the Andaman Sea. Steep-gradient, short rivers form floodplains of comparatively thin deposits of Quaternary sediments, and narrow bays backed by crescent shape sand ridges. This contrasts with the east coast where thick sequences of Quaternary fluvial and deltaic aggradational deposits, and Holocene progradational beaches, sand spits, tidal flats and lagoons, are indicative of tectonic subsidence with a coastal current transporting sediment into the region. Along the coastal Central Plain, the Chao Phraya delta is underlain by a thick Plio-Pleistocene deltaic and coastal marine sedimentary sequence. This has accumulated in a basin where the Quaternary tectonic environment is affected by epeirogenic uplift of the western highlands and tilting of the Central Plain. At the western Central Plains margin, rivers have formed distinct alluvial fans while the rest of the coastal plain has landscape features formed in the river delta-prograding coast environment that preceded the postglacial marine transgression.