The central plain of Thailand was formed over the last 8-7 kyr mainly by the deltaic processes of two major rivers, the Chao Phraya and the Mae Klong. The delta plain is the third largest delta plain in Southeast Asia after that of the Mekong and the Irrawaddy. On the basis of sedimentological and paleontological analyses of samples from three boreholes and all open-pit survey, the evolution of the delta was clarified with high-resolution C-14 dating.
After the maximum transgression at between 8 and 7 cal kyr BP, the delta system migrated southward into the paleo-Gulf of Ayutthaya. A large mud shoal (the Sananivate Mud Shoal) formed near the mouth of the paleo-gulf between 7 and 3 cal kyr BP and facilitated its infilling. As a result, the delta has prograded rapidly particularly during the last 2 kyr.
Deltaic sediment volume for the last 7.5 +/- 0.5 kyr shows that the average rate of sedimentation was 23.1 +/- 3.6 million t/yr, which is nearly the same as the present total sediment discharge from both rivers. The comparatively wide delta plain relative to sediment discharge resulted from the stable sea level, the shallow paleo-gulf acting as a receiving basin, and effective sediment trapping because of the mud shoal. (C) 2003 Elsevier Science Ltd. All rights reserved.