Tectonic Evolution of the Thonburi Basin in the Lower Central Plain, Thailand

Abstract

The Thonburi Basin, one of the Cenozoic basins in Central Thailand, covers the western part of Bangkok and eastern Samut Sakhon province. The interpretation of seventeen seismic reflection profiles (total length of 467 km), correlated with data from two well logs indicated that the Thonburi Basin is composed of five stratigraphic units. Unit A is the Oligocene shales and alternating thin layers of sandstone and limestone overlies uncomfomably beneath the Miocene alluvial plain deposits (Unit B). The fluvial deposits of units D and C, which are thicker to the western center of the basin and thin outwards to all directions overlie under the uppermost layer (Unit E) which is a thin Quaternary deposit. All units is about 1.0-2.5 sec (TWT) thick and is underlain by quartzite basement. This study indicates increased sedimentation of units A and B to the western side of the depocenter, and a relatively uniform deposition over the entire basin for the younger units (units C+D, and E). This stratigraphic setting is coupled with a presence of the western boundary normal fault that controls the rifting and was primary active between the Early Oligocene and the Pliocene. The E-W extension of the Thonburi Basin started just before the Oligocene and had been active until it ceased in the Late Miocene-Pliocene time. This evolution of the Thonburi Basin is consistent with those of other Tertiary basins in the Central Plain of Thailand.