Intense subaerial weathering of eolian sediments in Gale crater, Mars

Abstract

After over 8 years of successful surface operations on Mars, the Curiosity rover has revealed much about the environment in Gale crater. Despite early observations of a lacustrine environment, few of the subsequent deposits exhibit demonstrable lacustrine character. We suggest instead that most of the stratigraphic section explored to date can be best explained as eolian and/or volcaniclastic sediments subaerially chemically weathered by acidic precipitation in a reduced atmosphere. Most of the deposits in Gale crater seemingly did not form in an ancient lake, but the results nonetheless shed considerable light on ancient climate, environmental change, and the astrobiology of Mars. Discoveries by Curiosity provide a critical piece to Mars’ global alteration puzzle.

Ancient Winds, Waves, and Atmosphere in Gale Crater, Mars, Inferred From Sedimentary Structures and Wave Modeling

“…(2020) are correct that the Murray formation is older than the ripples, or if Liu et al. (2021) are correct that the Murray formation is aeolian, then substantial lacustrine deposition cannot be demonstrated to post‐date the thin atmosphere. Nevertheless, the thin atmosphere occurred prior to deposition of the ∼1‐m‐thick Dillinger member, which has also been interpreted as a subaqueous or mixed subaqueous/aeolian deposit (Heydari et al., 2020; Le Deit et al., 2016; Rice et al., 2017).…”

“…These beds are interpreted as lacustrine sediment that accumulated by fallout from suspension (Edgar et al., 2020; Fedo et al., 2018). Many hypotheses might explain why wave ripples are absent in these flat‐laminated beds: (a) the lake was too deep for waves to rework the bed, (b) sediment was too fine to form ripples large enough to be detected, (c) the lake surface was covered with ice, (d) the Murray formation is aeolian rather than lacustrine (Liu et al., 2021), or (5) winds were weaker when a lake was present. These hypotheses are considered in the following paragraphs.…”

“…Liu et al. (2021) argued that the Murray formation is dominantly aeolian rather than lacustrine. This would explain why parts of the section are devoid of wave ripples, but their argument for aeolian deposition is based in part on the presence of cross‐lamination and cross‐bedding.…”

“…If the depositional model of Grotzinger et al (2015) is correct, then deposition of the thin-atmosphere ripples at Kimberley was followed by deposition of more than 300 m of stratigraphically younger lake deposits of the Murray and Carolyn Shoemaker formations. On the other hand, if Heydari et al (2020) are correct that the Murray formation is older than the ripples, or if Liu et al (2021) are correct that the Murray formation is aeolian, then substantial lacustrine deposition cannot be demonstrated to post-date the thin atmosphere. Nevertheless, the thin atmosphere occurred prior to deposition of the ∼1-m-thick Dillinger member, which has also been interpreted as a subaqueous or mixed subaqueous/aeolian deposit (Heydari et al, 2020;Le Deit et al, 2016;Rice et al, 2017).…”

Ultraviolet Photooxidation of Smectite‐Bound Fe(II) and Implications for the Origin of Martian Nontronites

“…A second possible scenario is that UV radiation influenced the redox state of smectites newly forming by subaerial chemical weathering of basalts. Subaerial weathering has been proposed to explain smectite‐bearing mineral assemblages at a number of Martian sites (e.g., J. Liu et al., 2021; Lowe et al., 2020). UV radiation could have partially oxidized the neoformed smectites even under anoxic atmospheric conditions, either at the site of their formation or during detrital transport.…”