Tectonic Roles of Sediment Transport and Deposition in the Northern Andaman Sea and Eastern Bay of Bengal

The Ayeyarwady and Thanlwin rivers are considered to be the last remaining free flowing large rivers outside of the arctic and are the only major rivers to discharge into an active back-arc basin. Results from the recent research cruise (12/2017) show the Ayeyarwady River derived sediment accumulated not only in the Gulf of Martaban, but also in the Western Myanmar Shelf in the eastern Bay of Bengal. In contrast, deposition immediately off the river mouth is restricted, preventing Holocene mud accumulation in the middle and outer shelf.

Studies of the long-term geological tectonic history and recent uplift and subsidence of the Ayeyarwady Delta show: 1) Uplift induced by the oblique subduction of the Indian plate beneath the overriding southeast Asian plate has led to subsidence in the back-arc basin and created a 130-m-deep, 100-km-wide Martaban Depression. Extension created by the Andaman spreading center in the south has allowed for increased accommodation space within the depression where a 60-m-thick mud wedge has accumulated. 2) Conversely, uplift off the river mouth has led to shoaling and strong wave resuspension; therefore, sediment deposition adjacent the shelf is negligible. Instead, sediment is either diverted towards the Gulf of Martaban or along the western Myanmar coastline. 3) In the eastern Bay of Bengal, the subduction created deep sea trench may also receive sediment that has escaped from the western Myanmar shelf.