Orbital and In‐Situ Investigation of Periodic Bedrock Ridges in Glen Torridon, Gale Crater, Mars

Abstract

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300–3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind‐eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR‐forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater.

Statistical Analysis of APXS‐Derived Chemistry of the Clay‐Bearing Glen Torridon Region and Mount Sharp Group, Gale Crater, Mars

“…(2021) suggest silica‐poor brines as a means to convert clays along the ridge into iron oxides and oxyhydroxides, with recrystallization of ferric iron oxides enhancing cementation and thus preventing erosion. An assessment of the relative bedrock strength, inferred by the level of drill intensity required (Peters et al., 2018), confirm the inherent strength of Jura_VRR compared to Jura_GT (Stack et al., 2022). Targets within Glen Torridon range from <8 to 8.5 MPa, in contrast to the Jura_VRR drill target ( Rockhall ), which had an assessed strength of 8–12.5 MPa.…”

The Aeolian Environment in Glen Torridon, Gale Crater, Mars

“…Representatives of all of these aeolian components and processes characteristic of long‐term excavation of the trough are still present on the trough floor today, and were investigated by MSL. PBRs are the oldest aeolian features preserved on the trough floor (Stack et al., 2022). Brightly surfaced megaripples are considerably younger, and have cohesive, indurated interiors (revealed by wheel interactions) and decaying crater ejecta perched on their surfaces, indicating long‐term stability.…”

“…In addition to different saltation conditions occurring in the past, PBR crest orientations (typically ranging from NE‐SW to NNE‐SSW) are not aligned with nor orthogonal to present‐day sand migration mostly to the WSW. In some places megaripple orientations are approximately orthogonal to PBRs, but even if PBRs were formed by flow‐parallel winds (one of two possibilities evaluated by Stack et al., 2022), it is very unlikely that any of the megaripples are as old as the PBRs. Formative ages associated with PBR relief emerging gradually during erosional lowering of the trough floor must greatly exceed the ages of inactive megaripples currently perched on the trough floor today.…”

“…The rover encountered and crossed the contact between Jura mudstones of the Murray formation and the overlying, coarser‐grained Knockfarril Hill sandstone member of the Carolyn Shoemaker formation. Periodic Bedrock Ridges (PBRs, Montgomery et al., 2012) oriented approximately NE‐SW characterize the floor of Glen Torridon across much of this region (Stack et al., 2022). This segment of the traverse occurred during the local fall season of Mars Year 35.…”

Geology and Stratigraphic Correlation of the Murray and Carolyn Shoemaker Formations Across the Glen Torridon Region, Gale Crater, Mars

“…Just prior to Curiosity's arrival in GT, the team recognized three subdivisions within GT based on broad geomorphic similarities and spectral characteristics. The northeastern extent of GT associated with the CBU was divided into a smooth‐ridged unit with distinct NNE/SSW‐trending ridges (Stack et al., 2022), and a fractured unit with more topographic relief but less prominent ridges (light blue lines in Figure 4). From both orbital and ground perspectives, the “fractured intermediate unit” (FIU) that forms the southernmost part of GT is geomorphologically distinct with locally high topographic relief (contains prominent buttes) and has a comparatively higher albedo relative to the other GT units.…”