Quaternary sea-level fluctuations in the coastal area of eastern Thailand: a synoptic view in relation to mineral resources exploration

Abstract

The coast of eastern Thailand extends from Sattahip in the west to Ko Chang in the east. Its shoreline displays scalloped features and arches towards the southeast. The area consists of sediment-filled embayments (85%) separated by bedrock headlands (15%). Data from offshore mineral exploration during the 1988–1989 survey in area-1 of the Offshore Mineral Exploration in the Gulf of Thailand Project revealed some interesting evidence of sea-level fluctuations both onshore and offshore. An old beach barrier has been found at the water depth of about 20 m and at a distance of approximately 10 km offshore. This barrier has been traced and its trend appears likely to link rock outcrops at Hin Chalam in the west, through the southern tip of Ko Samet, and the outcrops at the middle of area 1-E in the east. This old shoreline is parallel to the present shoreline and is thought to have been formed during the postglacial marine transgression period in the early Holocene (6000–8000 yr BP) when sea-level was about 20 m lower than present. Some composite barriers have been located beyond a depth of 20 m and are evidence for Pleistocene interstadials. These interstadials would have influenced marine erosion of the inferred gem-bearing basalts found in area 1-E.