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

Abstract

The Glen Torridon stratigraphic sequence marks the transition from the low energy lacustrine-dominated Murray formation (Mf) (Jura member: Jm) to the more diverse Carolyn Shoemaker formation (CSf) (Knockfarril Hill member: Knockfarril Hill; Glasgow member: Glasgow). This transition defines a change in depositional setting. Alpha Particle X-ray Spectrometer (APXS) results and statistical analysis reveal that the bulk primary geochemistry of Mf targets are broadly in family with CSf targets, but with subtle compositional and diagenetic trends with increasing elevation. APXS results reveal significant compositional differences between Jura_GT and the stratigraphically equivalent Jura on Vera Rubin ridge (Jura_ VRR). The data define two geochemical facies (high-K or high-Mg), with a strong bimodal grain distribution in Jura_GT and Knockfarril Hill. The contact between Knockfarril Hill and Glasgow is marked by abrupt sedimentological changes but a similar composition for both. Away from the contact, the Knockfarril Hill and Glasgow plot discretely, suggesting a zone of common alteration at the transition and/or a gradual transition in provenance with increasing elevation in the Glasgow member. APXS results point to a complex history of diagenesis within Glen Torridon, with increasing diagenesis close to the Basal Siccar Point unconformity on the Greenheugh pediment, and with proximity to the beginning of the clay sulfate transition. Elemental mobility is evident in localized enrichments or depletions in Ca, S, Mn, P, Zn, Ni. The highly altered Hutton interval, in contact with the unconformity on Tower butte, is also identified on Western Butte, indicating that the "interval" was once laterally extensive.

Oxidized and Reduced Sulfur Observed by the Sample Analysis at Mars (SAM) Instrument Suite on the Curiosity Rover Within the Glen Torridon Region at Gale Crater, Mars

“…Geochemical analyses indicated that the GT region is compositionally similar to Murray formation rocks encountered earlier in the mission but with elevated abundances of crystalline phyllosilicates and minor changes in volatile chemistry indicative of a complex geologic history. Data from the Alpha Particle X-ray Spectrometer (APXS) showed that the GT region is geochemically similar to median Murray formation composition (Berger et al, 2020;O'Connell-Cooper et al, 2022). The Chemistry and Mineralogy (CheMin) X-ray Diffractometer (XRD) detected elevated abundances of phyllosilicates in the GT region, consistent with the orbital data, and lower amounts of hematite compared to the VRR (Thorpe et al, 2022).…”

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

“…Bedding in this location is less than about 10 cm thick and consists of stacked toesets of tabular-tangential cross-stratification. The top of this unit was drilled (Glen Etive) and studied extensively for (Dehouck et al, 2022;O'Connell-Cooper et al, 2022) and potential preserved organics (McAdam et al, 2022). While grain-size is difficult to determine through this interval, high-resolution MAHLI mosaics taken from centimeters from the outcrop surface, along with ChemCam RMI image mosaics, locally show dimpled outcrop textures suggestive of fine-to-medium sand.…”

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

“…The GT region shows a geochemical composition of the major elements that is broadly in line with the underlying Murray formation, but with some notable variability (e.g., Dehouck et al, 2021, this volume). In the Jura member, two endmembers have been identified from both the APXS and ChemCam measurements (e.g., Dehouck et al, 2021Dehouck et al, , 2022O'Connell-Cooper et al, 2022). These two endmembers were referred to as "rubbly" and "coherent" from the relative resistance to erosion of the corresponding rocks (Dehouck et al, 2022), with the "rubbly" consistently outcropping as small pieces of fragmented bedrock (e.g., Fig.…”

“…These two endmembers are mainly discriminated based on their MgO and K2O contents (Dehouck et al, 2021(Dehouck et al, , 2022O'Connell-Cooper et al, 2022). The "rubbly" endmember shows a K2O-rich (> 1.5 wt.%) and MgO-poor (usually <6 wt.%) composition, defined as the regional Type 2 composition by Dehouck et al, (2022).…”