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1320525 Neogene Sedimentary Fringe, West of Indo-Burma Ranges in Western Myanmar: Some Evidences for Late Cenozoic Synorogenic Sedimentation in Himalayan-Bengal System
- The Arakan Basin is one of the representative clastic 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- Burma 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 foraminifera zonation. Deep marine slope and shelf environments during early Miocene to middle Miocene (about 21.5 to 11 Ma) southward prograded shelf-delta environment during late Miocene to Pliocene time were determined. The early Miocene underthrusting along the Himalaya front is well documented by the forcedregressive 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 system tracts. These evolved through slope by-passing and slumping and, following deep-marine channel in-filling, began to accumulate an increased sediment load due to the rapid fall of the sea level by the uplifting in the hinterlands during the early- to early-middle-Miocene. The formation of a shelf-delta system marks a dramatic shift in the evolution of the southward prograding delta system following a eustatic sea-level low. In the foreland areas, erosional offloading with foreland uplifting caused a wide active fluvial system and formed transverse rivers distally in the late–middle- to late-Miocene.