BURIED PLEISTOCENE CHANNELS IN THE TONLE SAP LAKE, CAMBODIA: THEIR MORPHOLOGY AND SIGNIFICANCE

The Tonle Sap, the largest freshwater lake in Southeast Asia, relies on its unique connection to the Mekong River, via the Tonle Sap River, to attain its considerable size. Each year during the high flow maximum, the lake increases up to five fold in size as the flow from the Mekong reverses the flow of the Tonle Sap River. This connection is of great significance to the region culturally, with increased flow during the monsoon season leading directly to an extremely biologically productive ecosystem. Timing of the development of the area and the initiation of the currently observed flood-pulse system is disputed, with estimates for the establishment of this connection yielding dates as recent as 3,910 BP. However, little data exists that investigates the stratigraphy of Holocene sedimentation within the lake in order to better understand its evolution.

In this paper, we report on data collected in October 2014 from the Tonle Sap using the technique of Parametric Echosounding. This sub-bottom profiling technique was employed to survey the subsurface stratigraphy of the Tonle Sap and examine the link between the stratigraphy and previously collected sediment cores. The results have revealed the existence of a complex channel and valley network that has subsequently been infilled by predominately parallel-bedded, lacustrine sediments. This study discusses the tracing of this valley network surface, the nature of the infill of these valleys, the links between these results and seismic studies of Holocene lowstand valleys that have been found in the subsurface of the Mekong delta, and the significance of our new data for understanding the development of the Tonle Sap.