Grain size characteristics of surface sediments and net transport patterns in the southeastern Andaman Sea

The grain size of seafloor sediments is the most direct indicator of hydrodynamic pattern, which could effectively indicate the transport process of terrestrial detritus material at different time scales. Grain size was analyzed with the Malvern Mastersize 2000 particle size analyzer for 98 surface sediment samples collected from the southeast continental shelf, Andaman Sea. Results show that sediments on the southeast continental shelf could be divided into four categories: silty sand, sandy silt, silt, and mud. The grain size distribution of the study area revealed four distinct zones in terms of sediment texture: the northern shelf zone with relict sands; the southern inner shelf zone of mixed sediments with silty sand, sandy silt and silt; the Mergui Terrace zone with silt; and the continental slope zone with fine-grained and well-sorted mud. Based on the grain size analysis and Gao-Collins grain size trend analysis, the net transport patterns in the study area were discussed. The characteristic distance was defined less than 0.8° by geostatistical analysis and the results indicate that southwest area near Phuket was the depositional center of the southeastern Andaman Sea and the sediments displayed a net transport trend toward it. It was believed that the distribution and transport pattern of sediments in the study area were controlled by source supply, southwest monsoon currents, and tidal movement.