Evidence of coastal landforms and age determination related to the sea-level change at Nakhon Si Thammarat province in southern Thailand

Abstract

We present evidence of sea-level changes over the past 15,000 years from dating sandy beach sediments in Nakhon Si Thammarat province. First, we classified various types of coastal landforms from satellite images. The orientations of beach ridges and old lagoons are very important to understanding the evolution of sea-level rise and fall. In this area, there were two groups of old sandy beaches: (i) the inner beach, and (ii) the outer beach, which were separated by old lagoons. Then, nine quartz-rich samples were analyzed using Optically Stimulated Luminescence analysis to estimate the ages of deposition. The results supported the concept that the inner series of old sandy beach deposits indicated the onset of sea-level regression occurring approximately 15,000 years ago (YA). Sea level still stands, derived from the erosion of the beach ridge and deposition of old tidal flats, were estimated to be between 10,000 and 4,000 YA. The old lagoon showed a period of being covered from approximately 4,000 to 2,000 YA before outer beach ridge deposition some 2,000 to 400 YA during sea-level regression. Considering these measured ages, the sandy beach sediments yield the oldest range of depositional ages among all the Holocene beach deposits in southern Thailand.