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Deep-Water Channels “Swept” Downstream After Bend Cutoff in Salt Basins

Abstract

Deep-water channels have been known since the 1980’s to exhibit planform morphologic characteristics similar to rivers; however, some of the seminal papers about sinuous deep-water channels have stressed their unique migration style compared to their fluvial counterparts. This is important because the plan-view migration of channels, that is, expansion and downstream translation of bends (i.e., “sweep” and “swing”), as well as vertical movements by aggradation and incision, set the stratigraphic architecture of channelized depositional systems. For example, combined translation and expansion of river bends, with little aggradation, are thought to produce sheet-like sand bodies, whereas limited expansion and significant aggradation of deep-water-channel bends result in stacks of ribbon-like sand bodies. Although channel migration is often discussed in terms of expansion, translation, and rotation, a clear understanding of when and why channel bends expand or translate is still lacking. This is especially true for deep-water channels. Based on insights from rivers, we propose that downstream translation of bends might be common in settings that promote meander cutoffs and the generation of high-curvature bends. Such settings might include deep-water salt-tectonic provinces, in which rapid rates of deformation can create complex topography that localizes channel pathways and depocenters. Here, we use three-dimensional seismic-reflection data (PGS Investigação Petrolífera Limitada) from a region with salt-influenced topography in the Campos basin, offshore Brazil, to characterize the structural geometry of a salt diapir and stratigraphic architecture of an adjacent ~18 km-long reach of a deep-water-channel system. We interpret the structural and stratigraphic evolution, including meander-cutoff development near the salt diapir followed by ~10 km of downstream translation of a channel bend. We test the stratigraphic evolution with a simple numerical model of channel meandering. This integrated subsurface characterization and stratigraphic modeling study sheds light on the processes and controls of deep-water-channel downstream translation, which might be common in rapidly deforming settings, such as salt basins, that promote localized subsidence, meander cutoffs, and rapidly translating, high-curvature bends.