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Neogene syn-tectonic sedimentation in the eastern margin of Arakan-Bengal basins, and its implications on for the Indian-Asian collision in western Myanmar
- The Arakan Basin is one of the major sedimentary basins formed in the frontal part of the Himalayan orogenic belt since the Late Cenozoic. Defining one of the four major sedimentary basins of Myanmar, it is geomorphologically and tectonically differentiated from the others. The study area along the westernmost edge of Myanmar is separated from the Arakan Yoma (Indo–Burman Ranges) by a narrow coastal strip and is bordered by the Bay of Bengal to the west. Regional stratigraphic correlation and the geological age of the siliciclastic sequences were established based on planktonic foraminiferal zonation. Deep marine slope and shelf environments during Early- to Middle Miocene (ca. 21.5–11 Ma), and a southward prograded shelf–delta environment during Late Miocene to Pliocene time were determined. The Early Miocene underthrusting along the Himalayan front is well documented by the forced-regressive sedimentation patterns in the slope and shelf systems, sediments of which derived from the paleo-Ganges–Brahmaputra river systems in the Bengal–Arakan basins. Sequential evolution of the Miocene successions manifests in forced regressive wedged systems tracts. These evolved through slope by-passing and slumping and, following deep-marine channel in-filling, began to accumulate an increasing sediment load due to the rapid fall of sea level by the uplift in the hinterlands during the Early- to early-Middle-Miocene. The formation of a shelf–delta systems marks a dramatic shift in the evolution of the southward prograding delta systems following a eustatic sea-level low. In the foreland areas, erosional off-loading with foreland uplifting caused a wide active fluvial systems and formed transverse rivers distally in the late-Middle- to Late-Miocene.