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: KHm; Glasgow member: Gm), indicating a change in overall depositional setting. Alpha Particle X-ray Spectrometer (APXS) results and statistical analysis reveals 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 Jm GT and the stratigraphically equivalent Jura on Vera Rubin ridge (Jm VRR). APXS data defines two geochemical facies (high-K or high-Mg) with a strong bimodal grain distribution in Jm GT and KHm. The contact between KHm to Gm is marked by abrupt sedimentological changes but a similar composition for both. Away from the contact, the KHm and Gm plot discretely, suggesting a zone of common alteration at the transition and/or a gradual transition in provenance with increasing elevation in the Gm. 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 of 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.1

Evolved Gas Analyses of Sedimentary Rocks From the Glen Torridon Clay‐Bearing Unit, Gale Crater, Mars: Results From the Mars Science Laboratory Sample Analysis at Mars Instrument Suite

“…The GR drill area is known to be generally enriched in Mn (the MnO abundance detected in the GR drill sample by APXS was 1.07 ± 0.03 wt. %, O’Connell‐Cooper et al., 2022). One possible host would be trace or amorphous Mn oxides (Mn oxides were not detected by CheMin), and Mn can occur in several oxidation states in oxides.…”

“…MSL’s Alpha Particle X‐ray Spectrometer (APXS) instrument enabled determination of the bulk chemistry of drilled rock powders delivered to SAM, by analyzing drill fines dropped from the drill bit or drill tailings (e.g., O’Connell‐Cooper et al., 2022). In APXS analyses, a combination of alpha particles and X‐rays are used to excite emission of characteristic X‐rays from the elements in a sample.…”

“…In APXS analyses, a combination of alpha particles and X‐rays are used to excite emission of characteristic X‐rays from the elements in a sample. Total S and Cl measured by APXS (O’Connell‐Cooper et al., 2022) were compared to SAM EGA S and Cl abundances to assess what fraction of total S and Cl was attributed to SAM EGA detected phases. Additional information about the APXS instrument and its analyses are discussed elsewhere (Campbell et al., 2012, 2014; Gellert et al., 2006, 2015).…”

“…The stratigraphically lowest GT rocks, of the Jura member (Jm), had textures and bulk chemistry indicating that they are likely a continuation of the Murray formation (Mf) (e.g., Fox et al., 2020; O’Connell‐Cooper et al., 2022). The Murray formation in Mt.…”

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

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