Modern dispersal patterns of fine and coarse-grained sediments on the continental shelf off the Mekong River delta, South China Sea - insights from mineralogy, geochemistry and sediment budget

The Mekong River is one of the major suppliers of sediments to the ocean. The river delivers both fine- and coarse-grained sediment fraction, which may be distributed on the adjacent continental shelf in various ways and the objective of the study is to provide evidence of their dominating transport directions, sedimentation mode, as well as the sediment budget. Szczuciński et al. (2013) provided evidence of sediment dispersal of fine-grained sediments. They confirmed that a major portion of the supplied sediments is accumulated in the subaqueous delta front, which progrades directly off the river mouths and also forms at a distance of more than 200 km westward, next to the Camau Peninsula, provided evidence for the existence of a Mekong-fed prodelta further offshore and presented a quantitative assessment of the modern fluvial-derived fine-grained sediment dispersal on the continental shelf. This study extends the previous work and focus on dispersal of coarse-grained sediments. It presents insights from analyses of about 200 river bed sediment and marine surface sediment samples and short sediment cores collected from the delta front, prodelta, as well as from continental shelf further offshore. The sediments were analyzed for grain-size composition, bulk geochemistry and heavy minerals. Sediment accumulation rates were analysed with 210Pb and 137Cs. Dispersal pattern was interpreted mostly from statistical analyses of heavy mineral assemblages in various grain size fractions. They showed that the major transport direction is westward, along the delta front. Most of the deposits retain on the delta front with only a very minor portion stored in the prodelta. So, it differs from the fine-grained sediment budget calculation, which reveals that the subaqueous delta front stores approximately 50%, while roughly one-fourth of the sediments are retained in the subaerial region of the delta, and approximately 25% accumulates on the shelf around the Camau Peninsula, primarily in the form of prodelta deposits.

Szczuciński W., Jagodziński R., Hanebuth T.J.J., Stattegger K., Wetzel A., Mitręga M., Unverricht D., Phach P.V., 2013 - Modern sedimentation and sediment dispersal pattern on the continental shelf off the Mekong River delta, South China Sea. Global and Planetary Change, 110: 195-213