This research is the first to study the characteristics and origin of surface sediments in the UGOT. The results of sediment grain size, clay mineral, and heavy metal analyses are summarized as follows:
(1) The sediments become coarse from the northern coast to the sea with Mz increasing from 100 lm, which could be related to the fluvial input of sediment from the
drainage basin.
(2) The S/K ratio can be used as an indicator of the sediment in rivers in the study area. The ratio distribution illustrates that the sediments from Bang Pakong River and Mae Klong River are mostly concentrated on the eastern and western coasts, respectively, the sediments from the Tha Chin River is confined near the river mouth area, and the sediments from the Chao Phraya River are distributed in a tongue shape extending south to southwest of the study area.