Understanding Tectonic and Oceanographic Influenced Sediment Deposition throughout the Northern Andaman Sea

Southeast Asia is responsible for delivering approximately 25% of global riverine sediment discharge to the ocean annually. Of the four billion tons delivered, an estimated 600 million tons flows through the Ayeyarwady, Thanlwin, and Sittaung rivers. The Ayeyarwady and Thanlwin are considered to be the last remaining free-flowing large rivers in Asia outside of the arctic and are the only major rivers to discharge into an active back-arc basin. However, due to a variety of reasons, the region remains vastly understudied. The depositional nature of the system is believed to be controlled by a combination of oceanographic, climatic and tectonic processes. In the past, numerous studies have relied on these processes to infer that sediment discharged into the basin is transported across the Gulf of Martaban and deposited into the Martaban Canyon. Therefore, in December of 2017, a two-week research cruise was coordinated as a collaboration between North Carolina State University (NCSU), Virginia Institute of Marine Science (VIMS), and the University of Yangon, to better understand the fate and flux of sediment from these three major rivers.

The preliminary findings indicate; 1) highly reflective transgressive surfaces and a distinct transition in sediment composition seen in the CHIRP profiles indicate a clear transition zone between the relict and modern sediment within the Martaban Depression. 2) A compound, shelf-attached clinoform prograding rapidly into the Martaban Depression. The high accumulation rates and semi-consolidated sediment in this area suggest abrupt, periodic release of nearshore sediment seaward. 3) The weak lithosphere created by the evolving back arc basin has allowed for reduced coupling to the overriding plate underneath the Martaban Depression segment, compared to the southern Sumatran segment. As such, subsidence in the depression gradually increases, thereby increasing available accommodation space. 4) At the "Mouths of the Ayeyarwady," Holocene progradation of the delta has resulted in wave energy focused at the mouth due to the headland effect and its location relative to the incoming swell from the Bay of Bengal. Though aggradation of the subaerial delta has halted, uplift along the mouths have continued, causing shoaling and in effect, increased wave resuspension.