[H-GM02] 地形

[HGM02-P11] Sand ridges in the coastal zone of southern Thailand: The records of sea level history and environmental condition during the Late Quaternary

*Smith Leknettip¹、Sakonvan Chawchai¹、Montri Choowong¹、Daniela Mueller²、Alexander Fülling²、Frank Preusser² (1.Morphology of Earth Surface and Advanced Geohazards in Southeast Asia Center of Excellence (MESA CE), Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand、2.Institute of Earth and Environmental Sciences, University of Freiburg, Freiburg, Germany)

キーワード：Sand ridges, Luminescence dating, Sea level change, Holocene, Late Pleistocene, Sundaland

During much of the Quaternary period, the Thai-Malay Peninsular was connected to the Indonesian archipelago due to sea levels being at least 30 m lower than today. The submerged region is called Sundaland, which served as a land bridge and played a crucial role in the distribution of living creatures (e.g., flora, fauna, and humans) during the Quaternary. Nonetheless, information about past environmental conditions is limited due to the submerging and erosion of most sedimentary archives caused by past-glacial sea-level rise. This leads to controversy about environmental conditions during the Last Glacial and Interglacial periods. In this study, geomorphological mapping, sedimentology, and optically stimulated luminescence dating are combined to examine the evolution of sand ridges found in the coastal zone of Nakhon Si Thammarat Province in southern Thailand. The two main ridges (eastern and western ridges) are composed of moderately to poorly sorted medium to coarse and are classified as chenier ridges. The deposition of the eastern ridge occurred between ca. 8.3 ka and 2.9 ka, which was caused by coastal processes during the Holocene sea-level rise. The western ridge, however, has a minimum age of ca. 82 ka with further deposition dating back to the Last Glacial period. We believe that the development of the western ridge began during the Last Interglacial period (Marine Isotope Stage 5e). The sand accumulation on the ridge during the Last Glacial period was likely to be triggered by the aeolian processes. This would contribute to a discussion on the paleoclimatic and paleoenvironmental conditions supporting evidence for more arid and limited vegetation (savanna-like conditions) in the interior of Sundaland during the global-scale glacial periods.