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Floodplain deposits are recognized as potentially large sinks for fluvial sediments, yet spatial and temporal patterns of accumulation are not known for many river systems. In the tectonically active Bengal Basin, the Ganges and Brahmaputra rivers coalesce and have formed a large floodplain/delta complex, where widespread overbank flooding may deposit a significant portion of the river's estimated sediment discharge. To investigate the magnitude and distribution of this process, accumulation rates were determined by ¹³⁷Cs and ²¹⁰Pb radioisotope geochronology at 60 sites located in three regions of the Bengal Basin differing in age, physiography, and river influence. These geochronological methods have been applied to floodplain environments in only a few recent studies, and the present research offers a revised approach for heterogeneous systems. Patterns of sediment deposition in the Bengal Basin …