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A seismic stratigraphic analysis of 2600 km of data covering part of the Ganges-Brahmaputra delta has shown that it evolved in three stages. (1) The proto-Ganges delta developed immediately after the breakup of Gondwana at approximately 126 Ma. The Indian plate then moved rapidly northward, ultimately crossing more than 50 degrees of latitude. Because the catchment area was small, sedimentation was relatively restricted, and the early delta consists of relatively small-scale, prograding, clastic bodies alternating with mixed carbonate/clastic and carbonate-platform assemblages. (2) The transitional delta developed following a major eustatic sea level low at 49.5 Ma. Initially sedimentation was relatively restricted but, at about 40 Ma, the flux of water and clastic sedime ts dramatically increased, and the delta grew rapidly with the development of major prograding clastic depositional sequences. Abundant evidence of lobe switching suggests that the delta was stream dominated at that time. The abrupt change in the morphology of the delta appears to be a direct response to the collision of the Indian plate with the Eurasian plate, and the rise of the Himalayas. The delta remained stream dominated some time after the major plate collision and until the Bay of Bengal became a well developed deep embayment at about 21 Ma. The Bengal Fan began to accumulate during this interval as turbidity currents carried the increased sediment load into deeper water. (3) The modern delta began to appear in its present form following a major eustatic sea level low and erosio at 10.5 Ma. By this time, the delta had become tidally dominated and had prograded well beyond the study area into the now deeply embayed Bay of Bengal.
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