The evolution of Mun River in Southeast Asia, and its relationship with the environmental changes in the late Middle Pleistocene, based on sedimentologic and palynological evidences

摘要

The Mun River is located in the Khorat Plateau of mainland Southeast Asia. The watershed covers more than one third of this area. However, how the ancient river developed is still not so clear. In this study, a sandpit along the ancient river terrace at Bam Som, Tha Chang subdistrict, Chaloem Phra Kiat district, Nakhon Ratchasima province, Thailand is investigated with respect to the stratigraphy and sedimentology. The physical features of the sediment (particle size, sphericity, and sorted level) at different depths are analyzed and described. The layers composing the stratigraphic profile are classified based on the sedimentary profiles. Twenty two sampling layers classified into 3 members are recognized over 14 m depth. Three distinct river development cycles along the vertical section are identified along the vertical section. The stratigraphic stages correspond to the sedimentary members are suggested with the substances fining upwards. Generally, the stage at the bottom is shallow lake or flood plain deposit, the middle section represents a stage which is channel river deposit, and the upper section represents a stage which is dry land to aeolian deposit. Pollen records match well with fluvial development. The ancient river dynamics reconstruction is an approach to analysis the palaeoenvironment and will provide more information.