THE STRATIGRAPHIC EVOLUTION OF A SUBMARINE CHANNEL: LINKING SEAFLOOR DYNAMICS TO DEPOSITIONAL PRODUCTS

We investigate the relationship between the cross-sectional geomorphic expression of a submarine channel as observed on the seafloor and the stratigraphic product of long-lived erosion, bypass, and sediment deposition. Specifically, by reconstructing the time-space evolution of an individual channel fill (i.e., channel element) exposed in outcrop, we establish a genetic link between thick-bedded channel-element-axis sandstone to thinly interbedded channel-element-margin deposits. Although the bounding surface between axis sandstone and margin thin beds is sharply defined, it is composed of a series of geomorphic surface segments of various ages; as such, the composite stratigraphic surface (similar to 17 m relief) was formed from numerous incision events that repeatedly sculpted the conduit. By demonstrating the origin of the stratigraphic surface, we conclude that geomorphic surfaces with 2-7 m of erosional relief were largely responsible for the observed intra-channel-element architecture (and ultimately, the composite 17-m-thick element). The widely documented channel element axis-to-margin architecture is a product of submarine-channel thalweg dynamics, primarily recording interactions between the seafloor and the basal high-concentration layers of channelized turbidity currents.