CHANGES IN GEOMORPHOLOGY IN THE LOWER CENTRAL PLAIN OF THAOLAND CAUSED BY THE LATE HOLOCENE MARINE REGRESSION

Abstract

This study is aimed to understand the process of geomorphological changes of lower Central Plain of Thailand during the marine regression in the Late Holocene, especially in the areas which are located higher than the recent mean sea-level between 2 and 4 meters. Ten sedimentary sequences, approximately of 2 to 4 meter-long, were collected for sedimentary study and dating by the thermo luminescence method (TL). The result show that the sequences are homogenous, mainly consisting 2 layer: the lower one is characterized by brackish/marine clays and the upper one is freshwater floodplain sediments. TL dates show that the studied sedimentary sequences provide ages ranging from 2200-1200 BP, more or less contemporary with the contemporary with the Dvaravati Culture. The result suggest that the Lower Central Plain has been reached by the shallow sea between 1800-1500 BP in the areas which are higher than the recent mean sea-level between 2 and 4 meters in the western side and between 2-2.5 meters in the eastern side. However, the marine regression process during 1600-1200 BP caused the large freshwater in put into most part of the plain, and the position of palaeo-shoreline has been change downward to somewhere in the area southward Samphran District in Nakhon Pathom and Lamluka District in Pathum Thani