Isolated effects of gravity on sediment fluxes and delta morphology

Fluvial landforms on Mars are important because they indicate past liquid water. The landforms can provide information about past environmental and climate conditions and the potential for past life. Ancient fluvial sediment transport fluxes have been estimated for several channels on Mars. However, it is also important to understand the differences between sediment transport on Earth and Mars. Fluxes can differ significantly due to gravity, sediment density, lack of ecology and the possible presence of ice. Only when we understand the effects of such differences on sediment fluxes, we can apply and adapt knowledge of fluvial geomorphology on Earth to the surface of Mars. Additionally, such understanding will greatly improve the use of Earth analogues.

In this study, we isolate the effects of gravity on fluvial sediment transport with a 1D model of a simple static channel and a 2D depth-averaged numerical hydro-geomorphological model of a growing delta. The results show that sediment transport on Mars is more efficient than on Earth for the same water discharge, sediment distribution, and channel geometry. The 1D results show that mainly fine sediment is transported more efficiently on Mars, because the effect of gravity is stronger on suspended transport compared to bedload transport and bigger grains travel in suspension on Mars compared to Earth for the same boundary conditions. Because gravity affects fine and coarse sediment fractions differently, we also expect differences in geomorphology due to different ratios of sediment fractions and disparities in sediment sorting. We are exploring these morphological effects in our 2D delta model. Our preliminary results suggest that the lower gravity on Mars results in faster-growing deltas with lower slopes and wider channels. These results suggest that unexpected differences with Earth might also occur in the delta stratigraphy, which is important to realise when drilling for sediment samples in the search for biosignatures.