The morphological characteristics of Martian deltas. Comparison between experimental and Martian deltas

Abstract

The Martian surface features deltaic morphologies that formed in standing water bodies through the sediment transport of rivers. The gravitational force on Mars is lower than on Earth, which may influence the morphology of Martian deltas. However, a wide-scale study on the morphological characteristics of Martian deltas has not been done yet. This study aims to identify the key morphological characteristics of Martian deltas and compare them with experimental deltas, which are designed to test one effect of gravity. The experimental deltas are used to describe the relationship between grain size and the morphological characteristics. Furthermore, the trends between the morphological characteristics of the Martian and experimental deltas are compared. Lastly, based on the comparison of the Martian and experimental deltas, the grain size on the Martian deltas was predicted. A total of 78 Martian deltas and three time steps of ten different experimental deltas were studied. The experimental deltas consist of nutshell grains, serving as a proxy for Martian gravity, with a density of 1200 – 1400 kg/m3. Nine different mixtures were utilized to investigate the effects of grain size and distribution. The results indicate that different sediment compositions lead to changes in the delta slope, coastline rugosity, and channel width-to-depth ratio among the experimental deltas. Coarser sediments result in a steeper delta slope, more rugose shoreline and smaller channel width-to-depth ratios than fine sediments. Moreover, poorly sorted sediment mixtures result in steeper delta slopes and a more rugose shoreline compared to well-sorted sediment mixtures. For the experimental deltas, the delta slope increases for a more rugose coastline. Furthermore, the coastline elevation shows a larger spread in elevation for an increase in the grain size. The experimental deltas show different trends between morphological characteristics, compared to the Martian deltas. The experimental deltas display an increase in delta slope for an increase in coastline rugosity, while for the Martian deltas the delta slope decreases for an increase in coastline rugosity. The Martian deltas exhibit differences in morphology primarily based on delta type: stepped, prograding, or incised. Stepped and prograding deltas show a decrease in delta slope as coastline rugosity increases, while incised deltas may follow a similar trend to the experimental deltas. To make a prediction of the grain size on Martian deltas, three assumptions must be made: the deltas were formed under a steady water level, formed by a relatively constant discharge and formed by non-cohesive sediment. If these assumptions are met a prediction can be made. When the coastline is smooth and the delta slope is relatively low, the delta will probably have finer sediments. On the contrary, a delta with a rugose shoreline and steep delta slope is likely dominated by coarser sediments.