Remnant of the Late Holocene sand beach reveals ancient settlement-related sea level change from western Thailand

Archaeological findings and analysis of the sand beach at the Ban Khu Bua site in western Thailand indicate substantial sea-level shifts, which relate to sea-level regression during the late Holocene. This research focused on analyzing the paleo-shoreline and determining the age of ancient sandy beach deposits. Satellite imagery (Sentinel-2A) taken in 2021 facilitated classification of the paleo-coastal landforms into four main categories: colluvium, recent floodplain, old tidal flat, and old sandy beach. The latter, running predominantly north to south, is composed of fine to very fine sand characterized by sub-angular to round shapes, high sphericity, and well sorted. The sediment’s mineral composition is primarily quartz, accompanied by smaller rock fragments, organic matter, heavy minerals, and feldspars. Optically Stimulated Luminescence analysis of quartz-rich samples from the inner and outer areas suggested deposition of the old sandy beach sediments between 1,500 and 3,000 years ago in the inner part, pre-dating the establishment of the Khu Bua community in the Dvaravati period. Continuous beach sand deposition along Thao U-Thong Road aligns with the community settlement approximately 200 to 1,000 years ago.