Chapter 2 - The Geology of the Lower Mekong River

Abstract

This chapter provides a general overview of the tectonic and geological setting of the Mekong River south of the international border between the Peoples' Republic of China to the north and the Lao PDR (Laos) to the south. The modern river largely follows a course linking tertiary basins mediated by Cenozoic tectonism and is now set often within autogenic Quaternary and Holocene fluvial sediments. However, unusually for such a large river, much of the course within Thailand and Laos and parts of northern Cambodia is bedrock confined and the course is conditioned by the regional tectonic history. The usual major gradient and directional changes in the course of the river are tectonically controlled, whereas some rapids and local detail of channel planform are lithologically as well as tectonically controlled. The large supply of fluvially transported fine sediment is adding complexity to the Quaternary interpretation of the interaction of the river and the geology. The river today seems to carry very little coarse sand and gravel, the load being dominated by fine sands.