Abstract

Trails of depressions and associated sediment waves that follow the courses of underlying erosional submarine channels in Neogene strata in the Espirito Santo Basin on the Brazilian continental margin are described here. The features were imaged using three-dimensional seismic data, and they have a wavelength of several hundred meters and heights of tens of meters. Individual depressions are also found above knickpoints, scarps, and irregular top surfaces of mass-transport complexes. We propose that the depressions form initially as flute-shaped troughs of channel-confined sediment waves and develop into more circular depressions as a result of deposition on the shallow, upslope-facing stoss flanks and erosion or nondeposition in the lee flanks and the troughs. Depressions above topographical irregularities are interpreted to form when downslope-flowing currents encounter a break in slope, leading to excavation of a depression at the break and deposition of sediment downslope. This mechanism may be analogous to the formation of plunge pools and base-of-slope depressions. Similar features have been observed previously in several bathymetric data sets as well as created in numerical models and are thus considered ubiquitous in submarine settings.

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