An Insight Into Ancient Aeolian Processes and Post‐Noachian Aqueous Alteration in Gale Crater, Mars, Using ChemCam Geochemical Data From the Greenheugh Capping Unit

Abstract

Aeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed ∼3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Mars' history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was predominately sourced from an olivine‐rich unit that may be present farther up the slopes of Gale crater's central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity.

Evidence for Fluctuating Wind in Shaping an Ancient Martian Dune Field: The Stimson Formation at the Greenheugh Pediment, Gale Crater

“…All outcrops overlie the base Siccar Point group unconformity. However, it is uncertain whether the Greenheugh Stimson outcrops are time-equivalent to the northern Stimson outcrops: there is no way to correlate the outcrops with any degree of certainty, but geochemical analysis (Bedford et al, 2022) provide some indication that the Gleann Beag interval is correlative to the Stimson at the Emerson and Naukluft plateaus. (Bedford et al, 2022;Thompson et al, 2022).…”

“…All outcrops overlie the base Siccar Point group unconformity. However, it is uncertain whether the Greenheugh Stimson outcrops are time‐equivalent to the northern Stimson outcrops: there is no way to correlate the outcrops with any degree of certainty, but geochemical analysis (Bedford et al., 2022) provide some indication that the Gleann Beag interval is correlative to the Stimson at the Emerson and Naukluft plateaus. Analysis of the sedimentary architecture shows that the Greenheugh pediment capping unit contains three types of crossbedding, each representing deposition by morphologically distinct aeolian dunes. Compound cross‐strata were deposited by oblique compound dunes; planar simple cross‐bedding was deposited by straight‐crested simple dunes; trough cross‐bedding was deposited by either sinuous‐crested simple dunes, or as part of a compound dune; and concordant compound cross‐bedding, deposited by a dune formed by a fluctuating flow.…”

From Lake to River: Documenting an Environmental Transition Across the Jura/Knockfarril Hill Members Boundary in the Glen Torridon Region of Gale Crater (Mars)

“…Such episodic but important shifts in the local depositional conditions probably occurred at multiple points in Murray formation history, as indicated by lowstand deposits (Schieber, Bish, et al, 2017;Schieber, Stein, et al, 2017), desiccation cracks (Stein et al, 2018), and hypersaline interludes (Rapin et al, 2019). Cross-stratified aeolian sandstones of the Stimson formation (Siccar Point group, Figure 2; Banham et al, 2018Banham et al, , 2021Banham et al, , 2022Bedford et al, 2020Bedford et al, , 2022 have been observed to unconformably overlie the Murray and Carolyn Shoemaker formations in multiple places and elevations (as denoted by the two non-continuous placements illustrated on the column in Figure 2). They are remnants of an ancient aeolian sediment blanket, comparable to the current-day Bagnold active dune system (Figure 1b).…”

“…Cross‐stratified aeolian sandstones of the Stimson formation (Siccar Point group, Figure 2; Banham et al., 2018, 2021, 2022; Bedford et al., 2020, 2022) have been observed to unconformably overlie the Murray and Carolyn Shoemaker formations in multiple places and elevations (as denoted by the two non‐continuous placements illustrated on the column in Figure 2). They are remnants of an ancient aeolian sediment blanket, comparable to the current‐day Bagnold active dune system (Figure 1b).…”

Burial and Exhumation of Sedimentary Rocks Revealed by the Base Stimson Erosional Unconformity, Gale Crater, Mars

“…It is worth noting, however, that this chemical separation is not as applicable to other outcrops of the Stimson formation higher up on the slope of Mt. Sharp, for example, in the Greenheugh pediment region (Bedford et al., 2022).…”