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Using relative reflectance measurements from the Mastcam‐Z and SuperCam instruments on the Mars 2020 Perseverancerover, we assess the variability of Fe mineralogy in Noachian/Hesperian‐aged rocks at Jezero crater. The results reveal diverse Fe3+and Fe2+minerals. The igneous crater floor, where small amounts of Fe3+‐phyllosilicates and poorly crystalline Fe3+‐oxyhydroxides have been reported, is spectrally similar to most oxidized basalts observed at Gusev crater. At the base of the western Jezero sedimentary fan, new spectral type points to an Fe‐bearing mineral assemblage likely dominated by Fe2+. By contrast, most strata exposed at the fan front show signatures of Fe3+‐oxides (mostly fine‐grained crystalline hematite), Fe3+‐sulfates (potentially copiapites), strong signatures of hydration, and among the strongest signatures of red hematite observed in situ, consistent with materials having experienced vigorous water‐rock interactions and/or higher degrees of diagenesis under oxidizing conditions. The fan top strata show hydration but little to no signs of Fe oxidation likely implying that some periods of fan construction occurred either during a reduced atmosphere era or during short‐lived aqueous activity of liquid water in contact with an oxidized atmosphere. We also report the discovery of alternating cm‐scale bands of red and gray layers correlated with hydration and oxide variability, which has not yet been observed elsewhere on Mars. This could result from syn‐depositional fluid chemistry variations, possibly as seasonal processes, or diagenetic overprint of oxidized fluids percolating through strata having variable permeability. The oxidation states of the atmosphere and waters (whether rich or poor in oxidants such as oxygen) of Mars and their evolution are poorly constrained but can be recorded in the iron (Fe) mineralogy of rocks. Using data from the Perseverancerover, we analyzed the Fe mineralogy of ∼4–3 Ga old rocks from an ancient lake at Jezero crater. Oxidized Fe is found in igneous rocks and lowermost portions of sedimentary rocks, carried by clays and poorly crystalline oxides in the former and by sulfates and crystalline oxides in the latter, pointing to past action of oxidizing fluids, affecting more intensely the sedimentary rocks. Fe shows poor to no signs of oxidation in the uppermost strata, which might be evidence for a reducing atmosphere during sediment deposition or that the aqueous environment was too cold or too short‐lived to oxidize minerals. We also report Fe mineralogy variability at the cm‐scale in alternating colored layers, which has not been observed previously on Mars and could possibly mean that seasonal processes are recorded at Jezero crater. In situ reflectance data measured with Mars 2020 show variable Fe mineralogy in sedimentary rocks at Jezero craterStrata exposed at the fan front experienced stronger oxidative water‐rock interactions compared to the upper fan and igneous crater floorWe identify cm‐scale color banding correlated with Fe‐oxide variability that likely indicates time variation in redox In situ reflectance data measured with Mars 2020 show variable Fe mineralogy in sedimentary rocks at Jezero crater Strata exposed at the fan front experienced stronger oxidative water‐rock interactions compared to the upper fan and igneous crater floor We identify cm‐scale color banding correlated with Fe‐oxide variability that likely indicates time variation in redox

Early observations from the Perseverance rover suggested a deltaic origin for the western fan of Jezero crater only from images of the Kodiak butte. Here, we use images from the SuperCam Remote Micro‐Imager and the Mastcam‐Z camera to analyze the western fan front along the rover traverse, and further assess its depositional origin. Outcrops in the middle to lower half of the hillslopes comprise planar and inclined beds of sandstone that are interpreted as foresets of deltaic deposits. Foresets are locally structured in ∼20–25 m thick, ∼80–100 m long, antiformal structures interpreted as deltaic mouth bars. Above these foresets, interbedded sandstones and boulder conglomerates are interpreted as fluvial topset beds. One well‐preserved lens of boulder conglomerate displays rounded clasts within well‐sorted sediment deposited in overall fining upward beds. We interpret these deposits as resulting from lateral accretion within fluvial channels. Estimations of peak discharge rates give a range between ∼100 and ∼500 m3s−1. By contrast, boulder conglomerates exposed in the uppermost part of hillslopes are poorly sorted and truncate the underlying beds. The presence of these boulder deposits suggests that intense sediment‐laden flood episodes occurred after the deltaic foreset and topset beds were deposited, although the origin, timing, and relationship of these boulder deposits to the ancient lake that once filled Jezero crater remains undetermined. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. Early observations from the Perseverance rover of the Kodiak butte suggested a deltaic origin for the western fan of Jezero crater. Here, we use images from the SuperCam Remote Micro‐Imager and the Mastcam‐Z camera to analyze the western fan front along the rover traverse, and further assess its origin. We observe strata in the lower part of the fan front that we interpret as deltaic deposits formed below water in a lake. The strata of the upper part of the fan front contain sediments interpreted as fluvial deposits formed under various fluvial regimes, with some of them being deposited by the rivers that also fed the Jezero paleolake. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. New observations from the Perseverance rover of the western fan front confirm a deltaic originDeltaic foresets in the lower fan front are organized as antiformal structures interpreted as delta mouth barsSandstones and conglomerates in the upper part of the fan front suggest a highly variable fluvial input New observations from the Perseverance rover of the western fan front confirm a deltaic origin Deltaic foresets in the lower fan front are organized as antiformal structures interpreted as delta mouth bars Sandstones and conglomerates in the upper part of the fan front suggest a highly variable fluvial input

Sedimentary fans are key targets of exploration on Mars because they record the history of surface aqueous activity and habitability. The sedimentary fan extending from the Neretva Vallis breach of Jezero crater's western rim is one of the Mars 2020 Perseverance rover's main exploration targets. Perseverance spent ∼250 sols exploring and collecting seven rock cores from the lower ∼25 m of sedimentary rock exposed within the fan's eastern scarp, a sequence informally named the “Shenandoah” formation. This study describes the sedimentology and stratigraphy of the Shenandoah formation at two areas, “Cape Nukshak” and “Hawksbill Gap,” including a characterization, interpretation, and depositional framework for the facies that comprise it. The five main facies of the Shenandoah formation include: laminated mudstone, laminated sandstone, low‐angle cross stratified sandstone, thin‐bedded granule sandstone, and thick‐bedded granule‐pebble sandstone and conglomerate. These facies are organized into three facies associations (FA): FA1, comprised of laminated and soft sediment‐deformed sandstone interbedded with broad, unconfined coarser‐grained granule and pebbly sandstone intervals; FA2, comprised predominantly of laterally extensive, soft‐sediment deformed laminated, sulfate‐bearing mudstone with lenses of low‐angle cross‐stratified and scoured sandstone; and FA3, comprised of dipping planar, thin‐bedded sand‐gravel couplets. The depositional model favored for the Shenandoah formation involves the transition from a sand‐dominated distal alluvial fan setting (FA1) to a stable, widespread saline lake (FA2), followed by the progradation of a river delta system (FA3) into the lake basin. This sequence records the initiation of a relatively long‐lived, habitable lacustrine and deltaic environment within Jezero crater. Fan‐shaped deposits are important exploration targets on Mars because they record the activity of water and conditions suitable for life on the surface. The Mars 2020 Perseverance rover has been exploring an ancient impact crater, named Jezero, since landing on Mars in February 2021. One of the rover's main exploration targets is a fan‐shaped deposit of sedimentary rock extending into the crater from the western rim. One Earth year into the rover's mission, Perseverance arrived at the eroded edge of this fan, exploring several outcrops of sedimentary rock, and collecting seven rock samples. This study uses images and data from Perseverance to describe these rocks, called the “Shenandoah” formation, and to determine how they formed. The oldest rocks of the Shenandoah formation contain sand and pebbles that were likely laid down at the edge of an alluvial fan. Next, very fine‐grained rocks were deposited in a lake setting. Dipping layers of alternating sand and pebbles represent a change in the local setting and the growth of a delta into a relatively long‐lived lake. The rover's observations of the Shenandoah formation show that past conditions in Jezero crater were capable of hosting and preserving signs of ancient life. The Shenandoah formation is a sand‐dominated, clastic, sedimentary sequence comprising the lower 25 m of Jezero's western fanThis sequence records the transition from an alluvial fan setting to a lacustrine setting, followed by progradation of a river deltaThis sequence records evidence for a warm, wet, habitable depositional setting with the potential to preserve biosignatures The Shenandoah formation is a sand‐dominated, clastic, sedimentary sequence comprising the lower 25 m of Jezero's western fan This sequence records the transition from an alluvial fan setting to a lacustrine setting, followed by progradation of a river delta This sequence records evidence for a warm, wet, habitable depositional setting with the potential to preserve biosignatures

Silica enrichments resulting in up to ~90 wt% SiO2have been observed by the Curiosity rover's instruments in Gale crater, Mars, within the Murray and Stimson formations. Samples acquired by the rover drill revealed a significant abundance of an X‐ray amorphous silica phase. Laser‐induced breakdown spectroscopy (LIBS) highlights an overall correlation of the hydrogen signal with silica content for these Si‐enriched targets. The increased hydration of the high‐silica rocks compared to the surrounding bedrock is also confirmed by active neutron spectroscopy. Laboratory LIBS experiments have been performed to calibrate the hydrogen signal and show that the correlation observed on Mars is consistent with a silica phase containing on average 6.3 ± 1.4 wt% water. X‐ray diffraction and LIBS measurements indicate that opal‐A, amorphous hydrated silica, is the most likely phase containing this water in the rocks. Pyrolysis experiments were also performed on drilled samples by the Sample Analysis at Mars (SAM) instrument to measure volatile content, but the data suggests that most of the water was released during handling prior to pyrolysis. The inferred low‐temperature release of water helps constrain the nature of the opal. Given the geological context and the spatial association with other phases such as calcium sulfates, the opal was likely formed from multiple diagenetic fluid events and possibly represents the latest significant water‐rock interaction in these sedimentary rocks. Sedimentary rocks with high amorphous silica content were analyzed at Gale crater on MarsCalibration of the LIBS hydrogen signal reveals >4 wt% water content associated with silicaThe stability of opal‐A over several billion years is an anomaly relative to terrestrial mineralogy

Séítah is the stratigraphically lowest formation visited by Perseverance in the Jezero crater floor. We present the data obtained by SuperCam: texture by imagery, chemistry by Laser‐Induced Breakdown Spectroscopy, and mineralogy by Supercam Visible and Infrared reflectance and Raman spectroscopy. The Séítah formation consists of igneous, weakly altered rocks dominated by millimeter‐sized grains of olivine with the presence of low‐Ca and high‐Ca pyroxenes, and other primary minerals (e.g., plagioclase, Cr‐Fe‐Ti oxides, phosphates). Along a ∼140 m long section in Séítah, SuperCam analyses showed evidence of geochemical and mineralogical variations, from the contact with the overlying Máaz formation, going deeper in the formation. Bulk rock and olivine Mg#, grain size, olivine content increase gradually further from the contact. Along the section, olivine Mg# is not in equilibrium with the bulk rock Mg#, indicating local olivine accumulation. These observations are consistent with Séítah being the deep ultramafic member of a cumulate series derived from the fractional crystallization and slow cooling of the parent magma at depth. Possible magmatic processes and exhumation mechanisms of Séítah are discussed. Séítah rocks show some affinity with some rocks at Gusev crater, and with some Martian meteorites suggesting that such rocks are not rare on the surface of Mars. Séítah is part of the Nili Fossae regional olivine‐carbonate unit observed from orbit. Future exploration of Perseverance on the rim and outside of the crater will help determine if the observations from the crater floor can be extrapolated to the whole unit or if this unit is composed of distinct sub‐units with various origins. The Mars 2020 Perseverance rover landed on Mars in the Jezero crater on 18 February 2021. An important goal of this mission is to constrain the geology of the Jezero crater and its delta, and to sample rocks to return to Earth. Here, we study the deepest rock formation observed close to the landing site on the crater floor, named the Séitah formation. We conclude that this formation is igneous with rocks consisting in the accumulation of dominant millimeter‐sized olivine crystals with pyroxenes and other minerals. Such rocks form at depth by slow cooling of the magma, and the first mineral to crystallize (olivine) settles down by gravity in the magma. Such rocks bear similarity to other Martian rocks found in the Gusev crater by the Opportunity rover, and also to some Martian meteorites. These rocks will be studied in Earth‐based laboratories and will allow us to better understand magmatic processes on Mars. The Séítah formation consists of an olivine cumulate series, weakly altered, preserving the igneous texture and mineralogyEmplacement of the Séítah formation required fractional crystallization and slow cooling of the parent magma at depth and erosionThe Séítah formation could be a particular member of the Nili Fossae regional olivine‐carbonate unit observed from orbit The Séítah formation consists of an olivine cumulate series, weakly altered, preserving the igneous texture and mineralogy Emplacement of the Séítah formation required fractional crystallization and slow cooling of the parent magma at depth and erosion The Séítah formation could be a particular member of the Nili Fossae regional olivine‐carbonate unit observed from orbit

The Máaz formation consists of the first lithologies in Jezero crater analyzed by the Mars 2020 Perseverancerover. This formation, investigated from Sols (Martian days) 1 to 201 and from Sols 343 to 382, overlies the Séítah formation (previously described as an olivine‐rich cumulate) and was initially suggested to represent an igneous crater floor unit based on orbital analyses. Using SuperCam data, we conducted a detailed textural, chemical, and mineralogical analyses of the Máaz formation and the Content member of the Séítah formation. We conclude that the Máaz formation and the Content member are igneous and consist of different lava flows and/or possibly pyroclastic flows with complex textures, including vesicular and non‐vesicular rocks with different grain sizes. The Máaz formation rocks exhibit some of the lowest Mg# (=molar 100 × MgO/MgO + FeO) of all Martian igneous rocks analyzed so far (including meteorites and surface rocks) and show similar basaltic to basaltic‐andesitic compositions. Their mineralogy is dominated by Fe‐rich augite to possibly ferrosilite and plagioclase, and minor phases such as Fe‐Ti oxides and Si‐rich phases. They show a broad diversity of both compositions and textures when compared to Martian meteorites and other surface rocks. The different Máaz and Content lava or pyroclastic flows all originate from the same parental magma and/or the same magmatic system, but are not petrogenetically linked to the Séítah formation. The study of returned Máaz samples in Earth‐based laboratories will help constrain the formation of these rocks, calibrate Martian crater counting, and overall, improve our understanding of magmatism on Mars. The Mars 2020 Perseverancerover landed on Mars in the Jezero crater on 18 February 2021. The main goals of this mission are to constrain the geology of the Jezero crater and its delta, to search for biosignatures (evidence of ancient life), to sample rocks to return to Earth, and to prepare for human exploration. Here we study the rock formation observed at the landing site, named the Máaz formation. We conclude that this rock formation is igneous (=formed from cooling and crystallization of lava or magma) consisting of iron‐rich basaltic lava flows, formed through effusive (i.e., outpouring of lava without explosions) volcanism. When compared to other Martian magmatic rocks, these rocks show a large variety of textures (shape and size of minerals) and compositions, making them different from the Martian magmatic rocks studied so far. The various lava flows of the Máaz rocks are likely all related, but not related to the underlying Séítah rock formation. Perseverancehas collected core samples from the Máaz and Séítah rocks that could be among the Martian rocks to be returned to Earth in the 2030s. Their study in Earth‐based laboratories will allow us to better understand the evolution of Martian magmatism. The Máaz formation in Jezero crater consists of basaltic to basaltic‐andesite lava flows likely originating from the same parental magmaThe Máaz formation shows various igneous textures and has a different magmatic history than the other known Martian igneous rocksThe study of samples from the Máaz formation on Earth will help constrain the Martian cratering chronology and Martian igneous evolution The Máaz formation in Jezero crater consists of basaltic to basaltic‐andesite lava flows likely originating from the same parental magma The Máaz formation shows various igneous textures and has a different magmatic history than the other known Martian igneous rocks The study of samples from the Máaz formation on Earth will help constrain the Martian cratering chronology and Martian igneous evolution

The Perseverance rover landed in the ancient lakebed of Jezero crater, Mars on February 2021. Here, we assess the mineralogy of the rocks, regolith, and dust measured during the first year of the mission on the crater floor, using the visible and near‐infrared spectrometer of SuperCam onboard the Perseverance rover. Most of the minerals detected from orbit are present in the bedrock, with olivine‐bearing rocks at the bottom of the stratigraphy and high‐Ca pyroxene‐bearing rocks at the top. This is distinct from the overall low‐Ca pyroxene‐bearing composition of the watershed of Jezero and points toward an igneous origin. Alteration mineral phases were detected in most of the rocks analyzed in low proportions, suggesting that aqueous alteration of the crater floor has been spatially widespread, but limited in intensity and/or time. The diverse aqueous mineralogy suggests that the aqueous alteration history of the crater floor consists of at least two stages, to form phyllosilicates and oxyhydroxides, and later sulfates. We interpret their formation in a lake or under deeper serpentinization conditions and in an evaporative environment, respectively. Spectral similarities of dust with some rock coatings suggest widespread past processes of dust induration under liquid water activity late in the history of Jezero. Analysis of the regolith revealed some local inputs from the surrounding rocks. Relevant to the Mars Sample Return mission, the spectral features exhibited by the rocks sampled on the crater floor are representative of the diversity of spectra measured on the geological units investigated by the rover. We present the results of the analysis of rocks and regolith measured during the first year after landing of the Perseverance rover on Mars. The analytical technique used is reflectance spectroscopy (the measurement of the light reflected by surfaces), which primarily provides information on mineralogy. The mineralogical composition of the magmatic rocks located near the landing site indicates that they have experienced several distinct episodes of interaction with water in the past, of relatively low intensity. Soil analysis reveals a composition similar to what has been observed at other sites on Mars, with a contribution from the disintegration of local rocks. The samples that are collected by Perseverance at the crater floor and brought back to Earth are representative of the diversity of the different geological units explored by the rover. Mineralogy of rocks, regolith, and dust of the crater floor of Jezero, Mars was inferred from SuperCam reflectance dataAssemblages suggest limited aqueous alteration of igneous rocks, followed by evaporation‐induced deposition of sulfatesSamples collected on the crater floor for return to Earth are representative of the geological diversity and witness past‐aqueous processes Mineralogy of rocks, regolith, and dust of the crater floor of Jezero, Mars was inferred from SuperCam reflectance data Assemblages suggest limited aqueous alteration of igneous rocks, followed by evaporation‐induced deposition of sulfates Samples collected on the crater floor for return to Earth are representative of the geological diversity and witness past‐aqueous processes

Perseveranceexplored two geological units on the floor of Jezero Crater over the first 420 Martian days of the Mars2020 mission. These units, the Máaz and Séítah formations, are interpreted to be igneous in origin, with traces of alteration. We report the detection of carbonate phases along the rover traverse based on laser‐induced breakdown spectroscopy (LIBS), infrared reflectance spectroscopy (IRS), and time‐resolved Raman (TRR) spectroscopy by the SuperCam instrument. Carbonates are identified through direct detection of vibrational modes of CO3functional groups (IRS and TRR), major oxides content, and ratios of C and O signal intensities (LIBS). In Séítah, the carbonates are consistent with magnesite‐siderite solid solutions (Mg# of 0.42–0.70) with low calcium contents (<5 wt.% CaO). They are detected together with olivine in IRS and TRR spectra. LIBS and IRS also indicate a spatial association of the carbonates with clays. Carbonates in Máaz are detected in fewer points, as: (a) siderite (Mg# as low as 0.03); (b) carbonate‐containing coatings, enriched in Mg (Mg# ∼0.82) and spatially associated with different salts. Overall, using conservative criteria, carbonate detections are rare in LIBS (∼30/2,000 points), IRS (∼15/2,000 points), and TRR (1/150 points) data. This is best explained by (a) a low carbonate content overall, (b) small carbonate grains mixed with other phases, (c) intrinsic complexity of in situ measurements. This is consistent with orbital observations of Jezero crater, and similar to compositions of carbonates previously reported in Martian meteorites. This suggests a limited carbonation of Jezero rocks by locally equilibrated fluids. Carbonates are mineral phases that generally form by alteration of primary, magmatic minerals. This alteration process may occur under a variety of environmental conditions, which affect the resulting carbonate phase: its abundance, composition, spatial distribution and the mineral phases it is associated with. Consequently, carbonates keep track of the environmental conditions under which they formed, and in particular, the amount of CO2and liquid water involved in their formation. Understanding the history of both water and CO2on Mars is critical to better understand the evolution of the red planet and its atmosphere, but also the origin of the water on Earth, and possibly the origin of life. Since the beginning of the Mars2020 mission in Jezero Crater, the SuperCam instrument has analyzed more than 200 rocks of the crater floor, and detected carbonates along Perseverance's traverse. Carbonates are found in low amounts, and are therefore complex to identify; we use SuperCam's combination of investigation techniques and a specifically developed methodology to strengthen the identification of carbonate phases and their characterization. Even though Jezero crater hosted a lake billions of years ago, the detected carbonates appear to have formed in smaller amounts of water, after the lake had disappeared. Carbonates are detected along Perseverance's traverse in Jezero Crater with SuperCam using laser‐induced breakdown spectroscopy, IR and Raman spectroscopyCarbonate abundance is low overall, consistent with the weak carbonate signatures observed from orbit in the explored unitsThe detected carbonates have variable compositions within the magnesite‐siderite series, and likely reflect multiple alteration episodes Carbonates are detected along Perseverance's traverse in Jezero Crater with SuperCam using laser‐induced breakdown spectroscopy, IR and Raman spectroscopy Carbonate abundance is low overall, consistent with the weak carbonate signatures observed from orbit in the explored units The detected carbonates have variable compositions within the magnesite‐siderite series, and likely reflect multiple alteration episodes

During the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater‐based Martian chronology. We first review the previous estimation of crater‐based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology. Perseverance rover landed within Jezero crater (Mars) in 2021 and is collecting rocks that will be returned to Earth. In terrestrial state‐of‐the art labs, these rocks will be dated. It will allow to test the method planetary scientists are using to assess the age of Martian surfaces: their impact crater statistics. As impact craters are forming regularly, their statistics are used as a timeline in planetary sciences. The present paper studies the statistic of impacts craters within Jezero crater to reveal that the floor of Jezero has been protected from bombardment during years. These results imply that the collected rocks of the Jezero crater floor will not be ideal to test the method of using impact crater as chronometer of Martian surfaces. The dark floor unit of the Jezero crater displays an unusual inhomogeneous crater density, suggesting a complex exhumation historyThe crater density of the dark crater floor unit corresponds to the exposure time post exhumationThe crater density of this unit will not allow the calibration of the Martian crater chronology from return samples The dark floor unit of the Jezero crater displays an unusual inhomogeneous crater density, suggesting a complex exhumation history The crater density of the dark crater floor unit corresponds to the exposure time post exhumation The crater density of this unit will not allow the calibration of the Martian crater chronology from return samples

The Perseverancerover, Mars 2020 mission, landed on the surface of the Jezero crater, on 18 February 2021. This Martian crater is suspected to have hosted a paleolake as evidenced by the numerous detections of aqueously altered phases and thus is a promising candidate for the search for past Martian life. The SuperCam instrument, a collaboration by a consortium of American and European laboratories, plays a leading role in this investigation, thanks to its highly versatile payload providing rapid, synergistic, fine‐scale mineralogy, chemistry, and color imaging. After its landing, the first measurements of Martian targets with the infrared spectrometer of SuperCam (IRS) showed new instrumental behaviors that had to be characterized and calibrated to derive unbiased science data. The IRS radiometric response has thus been calibrated using periodic observations of the Aluwhite SuperCam Calibration Target (SCCT). Parasitic effects were understood and mitigated, and the instrumental dark and noise are characterized and modeled. The reflectance calibrated data products, provided periodically on the NASA Planetary Data System, are corrected for the main instrumental features. This radiometric calibration allowed us to study the 2.5 μm absorption band, which has been discovered in the Séítah unit and is associated with phyllosilicates‐carbonates mixtures. This paper is an instrumental investigation of the infrared spectrometer (IRS) portion of the SuperCam instrument on the Mars Science Laboratory Perseverance rover. Work performed prior to and during flight operations enabled the derivation of a proper instrumental response suitable for calibration of infrared point spectra of rocks and soils observed along the rover traverse. The paper describes development of a full data reduction pipeline in which the radiometric response, sensitivity of the IRS electronic board to temperature, and electromagnetic interference artifacts were removed. A companion paper (Mandon et al., 2022, https://doi.org/10.1029/2022JE007450) investigates the IRS data set through Sol 379 in more detail. Here, we specifically explore the 2.5 μm band attributed to carbonates in Séítah unit's phyllosilicate‐carbonates mixtures. We found that such mixtures likely have a low carbonate content, which may indicate low amounts of chemical alteration or an alteration by a carbon‐poor fluid. The infrared spectrometer of SuperCam on Perseverance has been successfully flight calibrated using the onboard calibration targetsCalibration permitted to study the most challenging long wavelengths and thus to discover an absorption band at 2.5 μmStudy of the 2.3 and 2.5 μm absorption bands showed the Séitah unit has variable clay and carbonate mixtures with low carbonate content The infrared spectrometer of SuperCam on Perseverance has been successfully flight calibrated using the onboard calibration targets Calibration permitted to study the most challenging long wavelengths and thus to discover an absorption band at 2.5 μm Study of the 2.3 and 2.5 μm absorption bands showed the Séitah unit has variable clay and carbonate mixtures with low carbonate content

Understanding the genesis of Martian soils is important to constrain the hydrogeologic history of the planet. Soils have the potential to record paleoenvironmental conditions, through the nature of secondary minerals formed during weathering. In situ X‐ray diffraction analyses in Gale crater have revealed that about one third of each soil sample is composed of amorphous materials containing hydrated phases. Here, we use the geochemical data from the ChemCam instrument to investigate the nature and origin of the hydrated amorphous phases. We report for the first time with ChemCam clues for the presence of sulfates within the amorphous component of soils. We show that sulfates are the main carrier of the soil hydration and possibly explain the nature of hydrogen and sulfur measured from orbit. These sulfates and the apparent lack of significant Al‐bearing weathering products are consistent with a model of soil formation including weathering of olivine in water‐limited acidic conditions. The study of Martian soils is of considerable interest as the nature of the mineral phases they contain, formed by the action of water for some of them, can give information on the past environments of the planet. Mineralogical analyses in Gale crater have shown that about one third of soils are composed of poorly crystalline materials whose nature remains unclear, and that soil hydration could be associated with these phases. Here, we use the chemical analyses from the ChemCam instrument to investigate the composition of the hydrogen‐bearing products, and we report for the first time the presence of sulfates in soils with this instrument. We demonstrate that sulfates are the main contributor to the water content of soils and are probably the source of the hydrogen and sulfur measured from orbit. The presence of sulfates and the lack of significant other secondary materials, especially enriched in aluminum, suggest that soils have probably undergone an acidic aqueous alteration with a low quantity of water, favoring the dissolution of olivine as the precursor to sulfates. The amorphous component of Gale crater soils contains hydrated sulfatesThe Eolian dust deposits are not the carrier of the identified hydrated sulfatesWater‐limited acidic conditions may have led to the formation of these phases The amorphous component of Gale crater soils contains hydrated sulfates The Eolian dust deposits are not the carrier of the identified hydrated sulfates Water‐limited acidic conditions may have led to the formation of these phases

Results from the Sample Analysis at Mars‐evolved gas analyzer on board the Mars Science Laboratory Curiosityrover constrained the alteration history and habitability potential of rocks sampled across the Siccar Point unconformity in Gale crater. The Glasgow member (Gm) mudstone just below the unconformity had evidence of acid sulfate or Si‐poor brine alteration of Fe‐smectite to Fe amorphous phases, leaching loss of Fe‐Mg‐sulfate and exchange of unfractionated sulfur 34S (δ34S = 2‰ ± 7‰) with enriched 34S (20‰ ± 5‰, Vienna Cañon Diablo Troilite). Carbon abundances did not significantly change (322–661 μgC/g) consistent with carbon stabilization by amorphous Al‐ and Fe‐hydroxide phases. The Gm mudstone had no detectable oxychlorine and extremely low nitrate. Nitrate (0.06 wt.% NO3), oxychlorine (0.13 wt.% ClO4), high C (1,472 μg C/g), and low Fe/Mg‐sulfate concentration (0.24 wt.% SO3) depleted in 34S (δ34S = −27‰ ± 7), were detected in the Stimson formation (Sf) eolian sandstone above the unconformity. Redox disequilibrium through the detections of iron sulfide and sulfate supported limited aqueous processes in the Sf sandstone. Si‐poor brines or acidic fluids altered the Gm mudstone just below the unconformity but did not alter underlying Gm mudstones further from the contact. Chemical differences between the Sf and Gm rocks suggested that fluid interaction was minimal between the Sf and Gm rocks. These results suggested that the Gm rocks were altered by subsurface fluids after the Sf placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations. The Curiosity Rover investigated the chemistry and mineralogy of rocks in the Glen Torridon region of Gale crater, Mars. Rocks sampled across an unconformity (representative of a time gap between when two sedimentary rocks were deposited) gave insight into how they were altered over time. The Glasgow mudstones, below the unconformity, were formed in a lake environment while the younger Stimson sandstones above the unconformity were formed from ancient sand dunes. Using the Sample Analysis at Mars Evolved Gas Analysis (SAM‐EGA) experiment, solid powdered samples from these rocks were heated and released gases (e.g., water, carbon dioxide, and sulfur dioxide) were tracked. These gases revealed a complex history of alteration through the rocks. The Glasgow mudstones were characterized by acidic or Si‐poor brine alteration, variable sulfur, low amounts of carbon, and no nitrate or oxychlorine. SAM‐EGA results from the Stimson sandstone showed rocks that were less altered, had higher levels of carbon, different sulfur compounds and sources, and some nitrate/oxychlorine. Together, these results suggested that the Glasgow rocks were altered by subsurface fluids after Stimson sandstone placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations. Subsurface silica‐poor brines or acidic fluids altered mudstones just below the Siccar Point group unconformityStimson formation sandstone above the unconformity was exposed to limited aqueous alterationAqueous alteration processes along the unconformity could have provided habitable conditions and in some cases, sufficient microbial C and N Subsurface silica‐poor brines or acidic fluids altered mudstones just below the Siccar Point group unconformity Stimson formation sandstone above the unconformity was exposed to limited aqueous alteration Aqueous alteration processes along the unconformity could have provided habitable conditions and in some cases, sufficient microbial C and N

The Glen Torridon (GT) region in Gale crater, Mars is a region with strong clay mineral signatures inferred from orbital spectroscopy. The CheMin X‐ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover, Curiosity, measured some of the highest clay mineral abundances to date within GT, complementing the orbital detections. GT may also be unique because in the XRD patterns of some samples, CheMin identified new phases, including: (a) Fe‐carbonates, and (b) a phase with a novel peak at 9.2 Å. Fe‐carbonates have been previously suggested from other instruments onboard, but this is the first definitive reporting by CheMin of Fe‐carbonate. This new phase with a 9.2 Å reflection has never been observed in Gale crater and may be a new mineral for Mars, but discrete identification still remains enigmatic because no single phase on Earth is able to account for all of the GT mineralogical, geochemical, and sedimentological constraints. Here, we modeled XRD profiles and propose an interstratified clay mineral, specifically greenalite‐minnesotaite, as a reasonable candidate. The coexistence of Fe‐carbonate and Fe‐rich clay minerals in the GT samples supports a conceptual model of a lacustrine groundwater mixing environment. Groundwater interaction with percolating lake waters in the sediments is common in terrestrial lacustrine settings, and the diffusion of two distinct water bodies within the subsurface can create a geochemical gradient and unique mineral front in the sediments. Ultimately, the proximity to this mixing zone may have controlled the secondary minerals preserved in sedimentary rocks exposed in GT. The Glen Torridon (GT) region on the lower slopes of the sedimentary mound in Gale Crater, Mars is characterized by terrains with enhanced clay mineral spectral signatures, as identified from orbit. This regional distinction in the landscape was confirmed on the ground with some of the highest clay mineral abundances measured to date by the CheMin X‐ray diffraction instrument onboard the Mars Science Laboratory rover, Curiosity. In addition to clay minerals, this region is unique because of two new phase identifications for CheMin: (a) Fe‐carbonates, which have been previously suggested from other instruments onboard Curiosity, but definitively identified for the first time with CheMin and (b) a new phase that has never been detected before on Mars. Even on Earth, few examples of this enigmatic phase exist, but here we modeled a mixture of clay minerals that were able to replicate the novel CheMin observations. Conceptually, a lake environment that interacts with discharging groundwater in the subsurface is an ideal setting to form the observed mineralogical trends in the GT region. Ancient lake and ground waters would have been geochemically distinct and the mixing of these water bodies in the sediments would have created unique mineralogical zones in the subsurface. Mineralogical overview of the Glen Torridon region, Gale crater, MarsThe Glen Torridon region is enriched in clay minerals and has a unique secondary mineral assemblageLacustrine‐groundwater mixing model is used to conceptualize regional variability and overall sedimentary history Mineralogical overview of the Glen Torridon region, Gale crater, Mars The Glen Torridon region is enriched in clay minerals and has a unique secondary mineral assemblage Lacustrine‐groundwater mixing model is used to conceptualize regional variability and overall sedimentary history

The Curiosity rover in Gale crater is investigating a mineral transition observed from orbit—an older “clay unit” to a younger “sulfate unit”—hypothesized to reflect the aridification of Mars' climate. Below this transition, the rover detected crystalline Ca‐sulfates with minor Fe‐sulfates but also found that some fraction of a rock's bulk SO3is often in the poorly constrained X‐ray amorphous component. Here, we characterize the abundances and compositions of the X‐ray amorphous sulfur‐bearing phases in 19 drilled samples using a mass balance approach, and in a subset of 5 samples using evolved SO2gas measured using the SAM instrument. We find that ∼20–90 wt% of a sample's bulk SO3is in the X‐ray amorphous state and that X‐ray amorphous sulfur‐bearing phase compositions are consistent with mixtures of Mg‐S, Fe‐S, and possibly Ca‐S phases, likely sulfates or sulfites. These phases reside in the bedrock, perhaps as cementing agents deposited with detrital sediments or during early diagenesis, and in diagenetic alteration halos deposited after lithification during late diagenesis. The likely presence of highly soluble Mg‐sulfates in the rocks suggests negligible fluid flow through the bedrock post‐Mg‐sulfate deposition. The X‐ray amorphous sulfur‐bearing phases probably became amorphous through dehydration in the current Martian atmosphere or inside the CheMin instrument. X‐ray amorphous sulfur‐bearing materials likely contribute to orbital spectral detections of sulfates, and so our results help form multiple hypotheses to be tested in the sulfate unit and are important for understanding the evolution of the Martian surface environment at Gale crater. The Curiosity rover in Gale crater, Mars is investigating a mineral transition observed from orbit—older clay‐rich to younger sulfur‐rich rocks—that likely reflects a change from a wetter to a drier Martian climate. In many of the sedimentary rocks investigated below the mineral transition, rover instruments identified different sulfur‐bearing phase assemblages. Inconsistencies indicate the presence of poorly constrained sulfur‐bearing phases that are undetected by the CheMin X‐ray diffraction instrument (X‐ray amorphous). To fully appreciate the significance of the transition to more sulfate‐rich rocks, we investigate the abundance and composition of X‐ray amorphous sulfur‐bearing phases at 19 drill sites below the transition. We find that most rocks have large fractions of X‐ray amorphous sulfur‐bearing phases that are likely mixtures of Mg‐, Fe‐, and possibly Ca‐sulfates or sulfites. In some rocks, these sulfur‐bearing phases might have precipitated from solutions delivered to the lake early on, acting to cement sediment grains. In other locations, X‐ray amorphous sulfur‐bearing phases are associated with zones where fluids altered the rocks long after they were cemented. These results help form multiple hypotheses to be tested in the sulfate‐rich rock unit and are important for understanding the evolution of the Martian surface environment at Gale crater. A large percentage of the bulk SO3in Gale crater sedimentary rocks is in the X‐ray amorphous state (20%–90%)X‐ray amorphous S‐bearing phases are likely mixtures of Mg, Fe, Ca, and other cation sulfates present as cement and in diagenetic featuresIn situ detections of X‐ray amorphous SO3likely contribute to orbital spectral detections of sulfates in lower Mount Sharp A large percentage of the bulk SO3in Gale crater sedimentary rocks is in the X‐ray amorphous state (20%–90%) X‐ray amorphous S‐bearing phases are likely mixtures of Mg, Fe, Ca, and other cation sulfates present as cement and in diagenetic features In situ detections of X‐ray amorphous SO3likely contribute to orbital spectral detections of sulfates in lower Mount Sharp

The CheMin instrument on the Mars Science Laboratory rover Curiositydetected ubiquitous high abundances (∼15–70 wt%) of X‐ray amorphous components (AmCs) in ancient sedimentary rocks of Gale crater. Mechanisms and timing of formation for the AmCs are poorly constrained, and could include volcanic, impact, or aqueous processes. We explore trends in AmC composition and abundance, and look for systematic compositional variation between sites within Gale crater. AmC compositions were estimated indirectly based on bulk chemistry and the nature and abundance of the crystalline phases for 19 sedimentary rock samples. AmC abundances positively correlate with AmC SiO2contents, and a mixing relationship appears to exist between SiO2‐rich and FeOT‐rich AmC endmembers. Endmember compositions are inconsistent with volcanic or impact glass alone, and so we conclude that the SiO2and FeOTcontents formed largely through aqueous processes. Cross‐cutting relationships and geologic context provide evidence that the most SiO2‐rich AmCs observed in Gale crater thus far may result from interactions with localized fluids during late diagenesis. AmCs with moderate to low SiO2contents likely formed earlier (before or soon after sediment deposition). Thus, the AmC SiO2and FeOTcontents in Gale crater rocks represent mixtures of sedimentary materials formed over most of the sedimentary history of Gale crater, starting before the first sediments were deposited in the crater (late Noachian), and ending well after the youngest sediments were lithified (at least mid‐Hesperian). However, it remains unclear how these metastable minerals have persisted through billions of years of diagenesis in Gale crater sediments. The CheMin instrument on the Mars Science Laboratory rover Curiositydetected ubiquitous high abundances (∼15–70 wt%) of amorphous materials in ancient sedimentary rocks of Gale crater. It is uncertain what geologic processes these materials represent (volcanic eruptions, impacts, or interactions with water), and when these materials were formed. Here we explore these possible formation mechanisms and their timing by estimating the chemical compositions of the amorphous materials, and looking for trends and variations in their compositions along the rover traverse. We find that amorphous iron‐ and silica‐rich materials formed mostly through interactions with water, and likely represent mixtures of chemical weathering products, chemical sediments, and cements that accumulated over time. We also find that some of the amorphous materials formed early on in the history of the crater, while others formed long after sediments were deposited and turned into rock, indicating that water persisted at Gale crater for ∼1 billion years. On Earth, it is thought that amorphous materials are readily converted into more crystalline materials in the presence of water, but it is unclear why this is not the case for Mars. X‐ray amorphous abundances are positively correlated with SiO2content, and amorphous SiO2and FeOTcontents are anticorrelatedX‐ray amorphous SiO2and FeOTcontents in Gale crater sedimentary rocks largely represent multiple aqueous processes occurring over timeIt is unclear how such metastable materials have persisted for billions of years X‐ray amorphous abundances are positively correlated with SiO2content, and amorphous SiO2and FeOTcontents are anticorrelated X‐ray amorphous SiO2and FeOTcontents in Gale crater sedimentary rocks largely represent multiple aqueous processes occurring over time It is unclear how such metastable materials have persisted for billions of years

The Curiosityrover investigated a topographic structure known as Vera Rubin ridge, associated with a hematite signature in orbital spectra. There, Curiosityencountered mudstones interpreted as lacustrine deposits, conformably overlying the 300 m‐thick underlying sedimentary rocks of the Murray formation at the base of Mount Sharp. While the presence of hematite (α‐Fe2O3) was confirmed in situ by both Mastcam and ChemCam spectral observations and by the CheMin instrument, neither ChemCam nor APXS observed any significant increase in FeOT(total iron oxide) abundances compared to the rest of the Murray formation. Instead, Curiositydiscovered dark‐toned diagenetic features displaying anomalously high FeOTabundances, commonly observed in association with light‐toned Ca‐sulfate veins but also as crystal pseudomorphs in the host rock. These iron‐rich diagenetic features are predominantly observed in “gray” outcrops on the upper part of the ridge, which lack the telltale ferric signature of other Vera Rubin ridge outcrops. Their composition is consistent with anhydrous Fe‐oxide, as the enrichment in iron is not associated with enrichment in any other elements, nor with detections of volatiles. The lack of ferric absorption features in the ChemCam reflectance spectra and the hexagonal crystalline structure associated with dark‐toned crystals points toward coarse “gray” hematite. In addition, the host rock adjacent to these features appears bleached and shows low‐FeOTcontent as well as depletion in Mn, indicating mobilization of these redox‐sensitive elements during diagenesis. Thus, groundwater fluid circulations could account for the remobilization of iron and recrystallization as crystalline hematite during diagenesis on Vera Rubin ridge. The NASA rover Curiosityinvestigated Vera Rubin ridge, a specific landform within the Gale crater on Mars. Scientific missions in orbit around the planet had previously discovered high concentrations of hematite on top of the ridge, an iron‐oxide mineral that commonly forms in water. However, it was not clear from orbit if such conditions existed at the time of the deposition of the sediments (around 3.5 billion years ago) or occurred much later during “diagenesis,” after deposition of the sediments and up to their transformation into rocks. On the surface, the rover did not observe significant differences between the ridge and the terrains encountered before it, except for small, dark geologic features that formed during diagenesis. Their analysis by the ChemCam instrument revealed that these features are composed of hematite—the same iron‐oxide mineral that was observed from orbit—and, interestingly, that the iron required to form them was removed from the adjacent rocks by groundwaters. As such, it appears that groundwaters played an important role in shaping Vera Rubin ridge, and thus partially obscure interpretations on the environmental conditions that existed on the surface of Mars at the time of sedimentation. Images from the Curiosityrover show the presence of dark‐toned diagenetic features at Vera Rubin ridgeChemCam analyses of these features point toward an Fe‐oxide composition, consistent with crystalline hematiteDepletion of Fe and Mn in bleached halos around the Fe‐oxide features indicates mobility of Fe and Mn during the later stages of diagenesis

Curiosity investigated a topographic rise named Vera Rubin Ridge (VRR) in Gale Crater, for which a distinct hematite‐like signature was observed from orbit. However, the Chemistry and Camera (ChemCam) and Alpha Particle x‐ray Spectrometer (APXS) instruments on board the rover did not record any significant iron enrichment in the bulk of the ridge compared to previous terrains. For this study, we have reverified ChemCam iron calibration at moderate abundances and developed more accurate calibrations at high‐iron abundances using iron‐oxide mixtures in a basaltic matrix in order to complete the ChemCam calibration database. The high‐iron calibration was first applied to the analysis of dark‐toned diagenetic features encountered at several locations on VRR, which showed that their chemical compositions are close to pure anhydrous iron oxides. Then, we tracked iron abundances in the VRR bedrock and demonstrated that although there is no overall iron enrichment in the bulk of the ridge (21.2 ± 1.8‐wt.% FeOT) compared to underlying terrains, the iron content is more variable in its upper section with areas of enhanced iron abundances in the bedrock (up to 26.6 ± 0.85‐wt.% FeOT). Since the observed variability in iron abundances does not conform to the stratigraphy, the involvement of diagenetic fluid circulation was likely. An in‐depth chemical study of these Fe‐rich rocks reveals that spatial gradients in redox potential (Eh) may have driven iron mobility and reactions that precipitated and accumulated iron oxides. We hypothesize that slightly reducing fluids were probably involved in transporting ferrous iron. Mobile Fe2+could have precipitated as iron oxides in more oxidizing conditions. Curiosity investigated a positive relief ridge named Vera Rubin Ridge (VRR) located in the Gale Crater. Orbital data indicate the presence of hematite (an iron oxide) in this ridge. Surprisingly, no significant enrichment in iron was observed by the two rover instruments (Chemistry and Camera [ChemCam] and Alpha Particle x‐ray Spectrometer [APXS]) that determined the chemical compositions. Here, we have made a dedicated iron calibration for ChemCam Martian data for high‐iron abundances. For this, we prepared mixtures of basaltic powder and iron oxides (hematite, goethite, or magnetite) and analyzed them with a ChemCam laboratory unit. The objective was to increase the set of standards currently used for ChemCam iron quantification. This method has shown that dark‐toned concretions located in some VRR bedrock have an iron abundance similar to pure hematite. An iron survey along the ridge revealed that there is no overall enrichment compared to underlying terrains. However, iron abundances recorded in the upper part of the ridge are more variable. Areas of enhanced iron abundances do not follow the rock stratification, which suggests that the phenomenon responsible for the iron variability did not occur during the sediment deposition but rather occurred later, during diagenesis. Fluids percolating into the sediment are most likely responsible for iron mobility. We present a dedicated ChemCam calibration for high‐iron abundances and apply it to Vera Rubin Ridge bedrock and diagenetic concretionsDark‐toned diagenetic features have iron contents close to pure anhydrous iron oxidesIron variability is observed among bedrock in the upper part of the ridge, attributed to iron mobility during diagenesis

The ubiquitous eolian dust on Mars plays important roles in the current sedimentary and atmospheric processes of the planet. The ChemCam instrument retrieves a consistent eolian dust composition at the submillimeter scale from every first laser shot on Mars targets. Its composition presents significant differences with the Aeolis Palus soils and the Bagnold dunes as it contains lower CaO and higher SiO2. The dust FeO and TiO2contents are also higher, probably associated with nanophase oxide components. The dust spectra show the presence of volatile elements (S and Cl), and the hydrogen content is similar to Bagnold sands but lower than Aeolis Palus soils. Consequently, the dust may be a contributor to the amorphous component of soils, but differences in composition indicate that the two materials are not equivalent. Eolian dust on Mars is very fine dust that covers the entire surface of the planet, gives it its typical red hue, and is mobilized by wind. It plays a significant role in the current rock cycle of the planet and for the temperature of the atmosphere. ChemCam uses a series of pulsed laser shots to analyze the chemical composition of target materials. Each first laser shot by ChemCam gives the composition of the deposited dust. These measurements have been constant over the duration of the Mars Science Laboratory mission. The dust is homogeneous at the millimeter scale (approximately the size of the ChemCam analysis spot). Compared to local soils and sands at Gale crater, the dust contains higher levels of iron and titanium, associated with volatile elements like hydrogen, sulfur, and chlorine. We infer from this difference that the dust does not entirely originate locally and may be part of a separate global cycle. The martian eolian dust chemical composition is homogeneous at the submillimeter scaleThe dust composition is different from the Aeolis Palus soils and Bagnold sands with a larger content of FeO and TiO2and lower hydrationAlthough dust may be a contributor to the amorphous component of soils, its composition indicates that the two materials are not equivalent