The effects of sediment supply and concentrations on the formation timescale of martian deltas

Abstract

We used a comprehensive 2-D and 3-D basin-filling morphodynamical model to explore the effects of changing hydrologic and sedimentary conditions on delta formation under martian conditions. Spatial and temporal deposition of sediment into a body of standing water was simulated using event-based time stepping (e.g. seasons). River and sediment discharge were calculated using the Darcy–Weisbach equation for width- and depth-averaged flow velocity and well-known and tested terrestrial sediment transport predictors modified for application to martian flows. A range in sediment grain sizes was determined from both landers and orbiting spacecraft data in order to include grain sizes typical of Mars and yet representative of the martian deltas. Several different scenarios of seasonal river discharge and sediment supply were explored to encompass a range of possible formation conditions.With the ability to track sediment as it is transported throughout the basin, it is apparent that non-negligible amounts of material are moved beyond the delta-forming region. This loss of sediment increased with river discharge, increasing the gap between the calculated and modeled formation timescales. These results have important implications for the formation timescales of the deltas and the small number of identifiable deltas on Mars today. Formation timescales that consider only the supply of sediment to the system and do not take into account factors affecting deposition and delta formation are underestimates of the actual amount of time needed to form the deposits. The lack of identifiable deltas in many paleolakes is likely a result of significant sediment transport beyond the channel mouth, causing the expected delta deposit to be draped throughout the basin.