Effects of sediment density on delta formation A comparison on the gravitational influence between Earth and Mars

Abstract

On Mars, several deltaic morphologies are observed. The deposits of these morphologies indicate sediment transport by river systems creating deltas in standing bodies of water. Comparison between Earth and Mars is possible, but the gravitational differences influence the sediments and their transport. This study aims to provide insight in the effects of lower particle density on delta morphology, as an approximate representation of decreased gravitation. The focus is on the impact of ’gravity’ on delta formation, analysing the advection length, depositional slope, channel behaviour and shoreline morphology. Eight experimental deltas are used to compare two different density sediments, sand (2650 kg/m3) and nutshell (1200-1400 kg/m3). Two different grain size distributions are used to analyse the effect between poorly sorted and uniform sediment in different gravitational conditions. In the final experiments, a fixed ”river mouth” is modelled to simulate natural inlet systems. The results of the experiments indicate changes in the delta formation by differences in sediment transport. First, the advection length increases, decreasing the depositional slope, by enhanced sediment transport and decreased settling velocities. The sediments are transported further into the basin by a higher efficient transport rate. Second, the channel system becomes more stable and less obstruction of the channel path occurs. High-density sediments show high avulsion rates, evenly spreading the sediments over the delta front creating smooth shorelines. The high settling velocity increases delta height by sediment deposition on the delta plain. Low-density sediments decrease the avulsion rate, as lower settling velocities result in less channel obstruction. The higher sediment mobility is expected to increase erosion, particularly for uniform sediment distributions, and therefore increase lateral migration. More stable channels increase the progradation over longer periods in one direction, creating more rugose shorelines and increasing shoreline length and surface area. The experiments demonstrate that lower gravity increases the mobilization of sediments, forming longer advection lengths and therefore lower depositional slopes. The delta forms lower delta plains and, with an increase in channel stability, a more rugose shoreline. The research provides insight into the formation of the observed deposits on Mars.