An insight into ancient aeolian processes and post‐Noachian aqueous alteration in Gale crater, Mars, using ChemCam geochemical data from the Greenheugh capping unit

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 likely 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

The Impact of Compositional Changes on Random Forest Predictions: Applicationto ChemCam LIBS Data from Gale Crater, Mars

We present statistics on ChemCam LIBS data from Gale crater. Predictions of a random forest classifier are compared to unsupervised clustering of the same data

Tensor Component Analysis for the Investigation of Depth Trends in ChemCam LIBS Data from Gale Crater, Mars

The laser-induced breakdown spectroscopy (LIBS) instrument ChemCam onboard NASA's Curiosity rover measures the chemical composition of Martian targets at remote distances. It ablates material with its laser and can therefore also measure depth profiles when targeting multiple times the same position. We included these so calles shot-to-shot trends as a third dimension in the ChemCam dataset and applied a tensor decomposition technique to it. With this method it is possible to detect correlations of elemental abundances with depth among multiple targets

Tensor component analysis as a tool for investigating depth trends in ChemCam LIBS data from Gale crater, Mars

We apply tensor component analysis (TCA) to ChemCam LIBS shot to shot data which allows to investigate depth trends in an unsupervised fashion

Askival: An altered feldspathic cumulate sample in Gale crater

Askival is a light‐toned, coarsely crystalline float rock, which was identified near the base of Vera Rubin Ridge in Gale crater. We have studied Askival, principally with the ChemCam instrument but also using APXS compositional data and MAHLI images. Askival and an earlier identified sample, Bindi, represent two rare examples of feldspathic cumulate float rocks in Gale crater with >65% relict plagioclase. Bindi appears unaltered whereas Askival shows textural and compositional signatures of silicification, along with alkali remobilization and hydration. Askival likely experienced multiple stages of alteration, occurring first through acidic hydrolysis of metal cations, followed by deposition of silica and possible phyllosilicates at low T and neutral‐alkaline pH. Through laser‐induced breakdown spectroscopy compositional analyses and normative calculations, we suggest that an assemblage of Fe‐Mg silicates including amphibole and pyroxene, Fe phases, and possibly Mg‐rich phyllosilicate are present. Thermodynamic modeling of the more pristine Bindi composition predicts that amphibole and feldspar are stable within an upper crustal setting. This is consistent with the presence of amphibole in the parent igneous rocks of Askival and suggests that the paucity of amphiboles in other known Martian samples reflects the lack of representative samples of the Martian crust rather than their absence on Mars

The Stimson formation at the Greenheugh pediment: stratigraphy, architecture, and correlation

International audienceThe Stimson formation, Gale crater represents the preserved expression of a major dune field which coalesced on the eroded flank of Mount Sharp [1-3]. This unit, which records spatial and temporal relations between interacting dunes can be used to gain insight into aeolian processes, interactions, and dune field construction processes on other planetary bodies. Here, the current understanding (as of spring 2022) of the Stimson formation at the Greenheugh pediment is summarized

The Stimson formation at the Greenheugh pediment: stratigraphy, architecture, and correlation

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

International audienceTemporal fluctuations of wind strength and direction can influence aeolian bedform morphology and orientation, which can be encoded into the architecture of aeolian deposits. These strata represent a direct record of atmospheric processes and can be used to understand ancient Martian atmospheric processes as well as those on Earth. The strata can: give insight to ancient atmospheric circulation, how the atmosphere evolved in response to global changes in habitability, and how ancient processes differ from modern processes. The Stimson formation at the Greenheugh pediment (Gale crater) records evidence of fluctuating wind across multiple temporal scales. The strata can be subdivided into three intervals-Gleann Beag, Ladder, and Edinburgh intervals. Internally, the intervals record changes of dune morphology and orientation, correlatable to wind fluctuations at multiple temporal scales. The basal Gleann Beag interval comprises compound cross-strata, deposited by oblique compound dunes. These dunes record a bimodal wind regime, resulting in net sediment transport toward the north. The Ladder interval records a reversal of sediment transport to the south, where straight-crested simple-dunes shaped by a seasonally variable winds formed. Finally, the Edinburgh interval records sediment transport to the west, where a unimodal wind formed sinuous-crested simple dunes. These observations demonstrate active and variable atmospheric circulation in Gale crater during the accumulation of the Stimson dune field, at multiple temporal scales from seasonally driven winds to much longer time-frames, during the Hesperian. These observations can be used to further understand ancient atmospheric conditions and processes, at a high temporal resolution on Mars

LEAVING GLEN TORRIDON: BEDROCK GEOCHEMISTRY MEASURED BY CHEMCAM EN ROUTE TO THE SULFATE UNIT OF GALE CRATER

International audienceSince January 2019, the Mars Science Laboratory (MSL) rover Curiosity has been exploring the Glen Torridon (GT) region of Gale crater, which corresponds to the topographic trough between the Vera Rubin ridge and the Greenheugh pediment (Fig. 1). From orbit, this region stands out due to the rela-tively strong near-infrared signatures of clay minerals [1,2]. The data collected on the ground by Curiosity have allowed the MSL team to confirm and quantify the presence of these clay minerals [3], to characterize their organic content [4], and to document in detail their geochemical and sedimentological settings [5].In particular, the bedrock chemistry measured by ChemCam shows elevated values of the Chemical Index of Alteration (CIA) throughout most of Glen Torridon [6,7], which indicates an open-system type of alteration [8]. In addition, the ChemCam observations suggest the presence of illite in the fine-grained rocks [9] and reveal a possible relationship between grain size and geochemical variations [10]. Finally, they show that the light-toned rocks located just below the uncon-formity at the base of the Greenheugh pediment (and drilled at Hutton; Fig. 1) are associated with “anoma-lous” bedrock compositions that may be related to a late-stage diagenetic event at Gale [7].Here, we report the findings of the ChemCam instrument during the last stretch of the GT campaign, from Bloodstone Hill to the Sands of Forvie (Fig. 1). At the conference, we will also present the data acquired in early 2021, as Curiosity approaches the transition into the sulfate-bearing unit

The Mineralogical Diversity of Jezero’s Western Fan Revealed by SuperCam/IRS, Perseverance Rover, and Spectral Modeling

International audienceThe Perseverance rover is currently exploring the top of the western sedimentary delta/fan of Jezero Crater. The aim is to characterize the stratigraphy and mineral composition of this formation to provide geologic context and collect a representative set of core samples to be returned to Earth. Among the instruments aboard the rover, SuperCam plays a key role in this study thanks to its remote measurement capabilities, including the near-infrared reflectance spectroscopy performed by the infrared spectrometer (IRS). This instrument analyzes light reflected from rocks and soils in the 1.3 – 2.6 μm spectral range, with a 1.15 mrad field of view. The IRS is sensitive to the spectral signatures of primary and alteration minerals, enabling the analysis of the compositional diversity of rocks and thus to the study of their formation conditions. We present here the results of this instrument, including minerals identified through linear spectral modeling and their relationship with stratigraphy.Linear spectral modeling fits a linear combination of library spectra on the IR spectra and allows estimates of the most likely mineral mixture describing the IR data. In the case of the Delta Front, the results were consistent with previous analyses (Dehouck et al., 2022, AGU conf.), but provided more detailed mineralogical identifications. The Yori Pass/Hogwallow Flats, Kaguyak and the lower Rocky Top members share a composition rich in Fe/Mg phyllosilicates (smectite, vermiculite), but also contain Fe/Mg-sulfates, anhydrite and a weak contribution from carbonates (the latter revealed by their 2.3 and 2.5 µm bands). In contrast, IR spectra of the Knife Creek and Devils Tanyard members (which are laterally equivalent) exhibited Fe/Mg phyllosilicates mixed with olivine and pyroxene, and a carbonate fraction, but lacked sulfates. The Amalik interval was unique and mainly marked by the presence of Mg-serpentines, mixed with Fe/Mg-phyllosilicates and Fe/Mg-carbonates. Higher in the stratigraphy, the Upper Fan units were characterized by Fe/Mg-carbonate deposits mixed with phyllosilicates and primary minerals, but no sulfates. This evolution of the spectral facies along the stratigraphy indicates a variation in alteration conditions during the deposition of these strata which are of interest for sampling by Perseverance