Development of a mass-balance framework for mixed bed and suspended load systems

Deposition in sedimentary basins leads to a down system decline in sediment flux, and fundamental changes in morphodynamics and stratigraphic architecture. Here, we quantify these changes for systems associated with significant suspended sediment transport, by expanding upon theory that links deposition to stratigraphic facies gradients for systems dominated by bedload transport. We place observations from a set of deltaic experiments into a mass-extraction framework, where distance from a basin entrance is mapped into the fraction of sediment supplied to a basin, deposited upstream of a given position. This transformation will also be used to examine downstream fining resulting from selective deposition. Experimental results come from two deltas constructed under identical forcing conditions with the exception of relative sea level (RSL) rise rates, which alter terrestrial accommodation generation. High RSL rise rates result in smaller delta-tops due to A) higher production rates of terrestrial accommodation, which provides space to store sediments and B) a reduction in the terrestrial trapping efficiency of suspended sediment pumped to overbank environments. The reduction in trapping efficiency is hypothesized to be linked to delta area through the advection settling distance of suspended particles leaving channels. Our preliminary results suggest that the dependency of terrestrial trapping efficiency on delta area influences facies gradients in a manner not captured in previously developed theory for bedload dominated systems. Our newly developed mass-extraction framework expands theory that links stratigraphic architecture to the interplay between accommodation and sediment supply, and will aid extraction of paleo-environmental and tectonic signals from stratigraphy.