PALEOENVIRONMENTS OF KHAO SAM ROI YOT NATIONAL PARK,CHANGWAT PRACHUAP KHIRI KHAN: EVIDENCE FROMPALEONTOLOGY, STRATIGRAPHY AND QUATERNARY DATING

Abstract

Khao Sam Roi Yot area and nearby consists of beach ridges and swales extending from Pran Buri, Sam Roi Yot to Kui Buri. Dating of sediment was carried out in this study by optically stimulated luminescence dating (OSL). Sediment samples were collected from 12 transects, including 48 samples at 3.8 km from the present shoreline. Total 10 samples of oyster shells collected from sea notch with the height 2.6 m from mean sea level were dated by carbon-14. Additional 25 stratigraphic columns from 9 transects were also carried out. As a result, the age of sediments around Kui Buri was between 880-7,940 years ago, at Sam Roi Yot of 1,940-6,260 years ago, and at Pran Buri, the age was at 1,850-10,200 years ago. Oyster shells from sea notch provide the age between 366-5,476 years ago. More than 57 species of molluscan, gastropods 12 species and bivalve 45 species were identified. They indicate mangrove environment to intertidal zone. The inner part of paleo-shoreline is located at 3.8 km from recent shoreline and about 2.6 m above men sea level. Environment has changed from mangroves to intertidal zone and then gradually to accumulate the ridges and swales periodically continues to recent shoreline. Paleo-landforms include coastal bay, a beach ridge plain and tombolos. The semi-circle paleo-coastal bay was also found. These new results suggest that the progradation of the SRY coastal plain came to a stillstand twice, between the middle and late Holocene. In addition, the beach ridge plain gradually advanced toward the sea in the east direction.