Mars sedimentary rock erosion rates constrained using crater counts, with applications to organic matter preservation and to the global dust cycle

TL;DR

This study uses crater counts to estimate erosion rates of Martian sedimentary rocks, revealing implications for organic matter preservation and dust cycle dynamics, with erosion rates around 100 nm/yr over large scales and long timescales.

Contribution

It introduces a crater count-based method to estimate erosion rates of Martian rocks, accounting for crater obliteration, and applies this to understand organic preservation and dust production.

Findings

Erosion rates of ~100 nm/yr for Martian sedimentary rocks.

Crater counts fit a model balancing crater production and obliteration.

Dust production in Mars's past exceeds current dust reservoirs.

Abstract

Small-crater counts on Mars light-toned sedimentary rock are often inconsistent with any isochron; these data are usually plotted then ignored. We show (using an 18-HiRISE-image, >10^4 crater dataset) that these non-isochron crater counts are often well-fit by a model where crater production is balanced by crater obliteration via steady exhumation. For these regions, we fit erosion rates. We infer that Mars light-toned sedimentary rocks typically erode at ~10^2 nm/yr, when averaged over 10 km^2 scales and 10^7-10^8 yr timescales. Crater-based erosion-rate determination is consistent with independent techniques, but can be applied to nearly all light-toned sedimentary rocks on Mars. Erosion is swift enough that radiolysis cannot destroy complex organic matter at some locations (e.g. paleolake deposits at SW Melas), but radiolysis is a severe problem at other locations (e.g. Oxia Planum). The data suggest that the relief of the Valles Marineris mounds is currently being reduced by wind erosion, and that dust production on Mars <3 Gya greatly exceeds the modern reservoir of mobile dust.