Three main rivers-the Ganges, Brahmaputra, and Meghna-coalesce in the Bengal basin to form the world's largest delta system, which serves as fi lter and gateway between the Himalayan collision and vast Bengal fan repository. New insights into the Holocene construction of the Ganges-Brahmaputra-Meghna delta, with a focus on river sedimentation, channel migration, and avulsion history, are presented here using the Sr geochemistry of bulk sediments as a provenance tracer. The sediment load of each river transmits a distinct Sr signature owing to differences in source rocks from the Himalaya, Tibet, and local regions, allowing for effective tracking of river channels and stratigraphic development within the delta. In the early Holocene, vigorous delta aggradation occurred under rapid sea-level rise and high river discharge and supported the construction of sand-dominated stratigraphy by laterally mobile, braided-stream channels. However, the vertically (i.e., temporally) uniform, but geographically distinct, Sr signatures from these deposits indicate that the Ganges, Brahmaputra, and Meghna fl uvial systems remained isolated from one another and apparently constrained within their lowstand valleys. By the mid-Holocene, though, delta stratigraphy records spatially and temporally nonuniform Sr signatures that hallmark the onset of avulsions and unconstrained channel migration, like those that characterize the modern Ganges and Brahmaputra fl uvial systems. Such mobil-ity developed in the mid-Holocene despite declining discharge and sea-level rise, suggesting that earlier channel behavior had been strongly infl uenced by antecedent topography of the lowstand valleys. It is only after the delta had aggraded above the valley margins that the fl uvial systems were able to avulse freely, resulting in numerous channel reorganizations from mid-Holocene to present. These channel-system behaviors and their role in delta evolution remain coarsely defi ned based only on this initial application of Sr-based provenance tools, but the approach is promising and suggests that a more complete understanding can be achieved with continued study.

Analogs-ancient and modern-are key to our understanding and interpretation of the stratigraphic record, which is too often incomplete and sparingly exposed. Here we describe an upwardcoarsening Holocene delta sequence that sits unconformably on another, remarkably comparable, delta sequence of Pleistocene age. Such a complete and well-preserved Pleistocene example is rare given extended periods of sea-level lowstand and fluvial incision during the past 200 ka.These stacked delta sequences allow us to consider how analogous our well-studied Holocene analogs are.The comparison reveals a nearly identical facies succession, with modest differences only in the relative timing of delta response to rising sea level. One key difference, though, is a unique facies in the Pleistocene sequence suggesting that major floods from the Himalayas impact the Bengal margin, perhaps periodically, during glacial-interglacial climate transitions.