A 2.5D Seismic Exploration of the Ayeyarwady River Subaqueous Delta in the Andaman Sea

Southeast Asia retains one of the most active fluvial environments in the entire world. Combined, the three major rivers, Ayeyarwady, Thalween, Sittaung in the Myanmar region deliver the 3^rdmost sediment annually, almost 600MT/yr, into the ocean. Unfortunately, this area is vastly understudied. Therefore, in December of 2017, a 2-week research cruise was conducted to better understand the areas complex geomorphology, tectonics, and sediment fate. On this cruise, over 1500km of CHIRP data was collected along with 30 sediment cores. Here we present you a 2.5D view of our high-resolution CHIRP sonar profiles to indicate the distribution and stratigraphic sequences. Our preliminary data relates 1) The Ayeyarwady and Thalween combined, create a classic clinoform with a topset, foreset, and bottomset in the Gulf of Martaban of the Northern Andaman Sea. 2) The Ayeyarwady river sediment also is transported northward along the eastern margin of the Gulf of Bengal and eastward to the deep sea. 3) We found significant and extensive fault systems in the subaqueous deltaic deposits. Unlike the adjacent Ganges-Brahmaputra subaqueous delta, there is no slumping or failure. Instead, the clinoform has aggradated steadily. The depositional rate is up to 10cm/yr. in the foreset. 4) In the Andaman Sea, there is no evidence to suggest that the modern sediment has escaped into the Martaban Canyon; However, along the Bay of Bengal, there is clear evidence to suggest modern sediment escaping into the subduction trench. This analysis will therefore provide a unique, 2.5-dimensional view of the geomorphology and historical sequence-stratigraphy of the Andaman seafloor through the eyes of the CHIRP acoustic seismic imagery.