Manganese-Iron Phosphate Nodules at the Groken Site, Gale Crater, Mars

The MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe2+,Mn2+)3(PO4)2·8H2O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. ChemCam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO2 and Al2O3 abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodules’ non-silicate components, shows high concentrations of MnO, P2O5, and FeO and a molar ratio P/Mn = 2. Visible to near-infrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO2). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodules’ mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, (Fe2+,Mn2+)3(PO4)2·8H2O and –6H2O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidized—first to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments

CHEMISTRY OF MANGANESE-BEARING MATERIALS AT THE GROKEN DRILL SITE, GALE CRATER, MARS

International audienceIn July 2020, the Curiosity rover encountered a region of bedrock that contained an abundance of layered nodular features and highly unusual Mn- and sometimes P-rich chemistries (Fig.1a) in Glen Torridon (GT), a phyllosilicate-rich mudstone to sandstone deposit [1]. This sampling location was originally targeted at a distance as a site for the Sample Analysis at Mars (SAM) instrument to perform one of its two tetramethylammonium hydroxide (TMAH) wet chemistry experiments [2] in the hopes that the new location would provide similar rocks to the previously analyzed clay-rich Glen Etive targets at approximately the same elevation [3]

Initial Major Element Quantification Using SuperCam Laser Induced Breakdown Spectroscopy

International audienceSuperCam uses Laser Induced Breakdown Spectroscopy (LIBS) to collect atomic emission spectra from targets up to ~7 meters from the Perseverance rover. Due to the complexity of LIBS physics and the diversity of geologic materials, we use an empirical approach to major element (SiO2, TiO2, Al2O3, FeOT, MgO, CaO, Na2O, K2O) quantification, based on a suite of 1198 SuperCam laboratory spectra of 334 standards, including the rover calibration targets. SuperCam LIBS spectra are pre-processed by subtracting "dark" (passive/non-LIBS) spectra, denoising, continuum removal, instrument response correction, conversion to radiance, and wavelength calibration. For quantification, the spectra are masked to remove noisy sections of the spectrum and normalized by dividing signal in each spectrometer by the total signal from that spectrometer. We also found that the additional preprocessing steps of peak binning and/or per-channel standardization improved the results in some cases. These data are used to train multivariate regression models, with parameters optimized using cross-validation to avoid overfitting. We considered a variety of regression algorithms including Partial Least Squares (PLS), Least Absolute Selection and Shrinkage Operator (LASSO), Ridge, Elastic Net, Support Vector Regression (SVR), Random Forest (RF), Gradient Boosting Regression (GBR), Local Elastic Net, and blended sub-models. Models were selected based on test-set performance, accuracy of predictions of the onboard calibration targets, comparison of Mars and laboratory spectra, and the geochemical plausibility of Mars results. In some cases we found that the average of the predictions of several algorithms gave better results than any single method. Accuracy of predictions is estimated as the root mean squared error of prediction (RMSEP) for the test set. As additional spectra are collected from Mars, we continue to validate and improve upon this initial SuperCam elemental quantification. Areas of investigation include calibration transfer, probabilistic regression methods, and regression models for additional elements.Figure 1: Test set predictions vs actual compositions for each major element. Perfect predictions would fall on the line. RMSEP measures the accuracy of the model in wt.%

Initial Major Element Quantification Using SuperCam Laser Induced Breakdown Spectroscopy

International audienceSuperCam uses Laser Induced Breakdown Spectroscopy (LIBS) to collect atomic emission spectra from targets up to ~7 meters from the Perseverance rover. Due to the complexity of LIBS physics and the diversity of geologic materials, we use an empirical approach to major element (SiO2, TiO2, Al2O3, FeOT, MgO, CaO, Na2O, K2O) quantification, based on a suite of 1198 SuperCam laboratory spectra of 334 standards, including the rover calibration targets. SuperCam LIBS spectra are pre-processed by subtracting "dark" (passive/non-LIBS) spectra, denoising, continuum removal, instrument response correction, conversion to radiance, and wavelength calibration. For quantification, the spectra are masked to remove noisy sections of the spectrum and normalized by dividing signal in each spectrometer by the total signal from that spectrometer. We also found that the additional preprocessing steps of peak binning and/or per-channel standardization improved the results in some cases. These data are used to train multivariate regression models, with parameters optimized using cross-validation to avoid overfitting. We considered a variety of regression algorithms including Partial Least Squares (PLS), Least Absolute Selection and Shrinkage Operator (LASSO), Ridge, Elastic Net, Support Vector Regression (SVR), Random Forest (RF), Gradient Boosting Regression (GBR), Local Elastic Net, and blended sub-models. Models were selected based on test-set performance, accuracy of predictions of the onboard calibration targets, comparison of Mars and laboratory spectra, and the geochemical plausibility of Mars results. In some cases we found that the average of the predictions of several algorithms gave better results than any single method. Accuracy of predictions is estimated as the root mean squared error of prediction (RMSEP) for the test set. As additional spectra are collected from Mars, we continue to validate and improve upon this initial SuperCam elemental quantification. Areas of investigation include calibration transfer, probabilistic regression methods, and regression models for additional elements.Figure 1: Test set predictions vs actual compositions for each major element. Perfect predictions would fall on the line. RMSEP measures the accuracy of the model in wt.%

Metal Enrichment of Wave-Rippled Sediments on Ancient Mars

International audienceThe Curiosity rover is ascending a sedimentary-rock mountain, Mount Sharp, testing hypotheses about how and why Mars' surface dried out. Within the past year, Curiosity has investigated an apparently Mount-Sharp-spanning feature - the Marker Band, which frequently forms a topographic bench. The Marker Band is distinctive in its lateral extent, stratigraphic confinement, and nontrivial thickness. The Marker Band also shows a distinct metal-rich geochemistry unlike any other materials previously analyzed by the rover, and its lower part exhibits wave ripples extending across hundreds of meters (possibly kilometers). Thus, the Marker Band is a marker of a change in the environment within Gale crater from drier conditions that formed underlying sulfates to wetter conditions that formed wave ripples (Gupta et al. this conference). Wave ripples do not persist above the rippled Marker Band, but further clues regarding the evolution of Mars' carbon cycle and atmosphere are obtained from carbonate in drilled samples immediately above the rippled Marker Band (Tutolo et al., this conference), which is strongly elevated in δ13C (Burtt et al., this conference). APXS data for drill fines from ~1 cm depth within the rippled layers show >40 wt% FeO, ~2 wt% Zn, and >1 wt% MnO (Thompson et al., LPSC 2023); metal enrichment is also seen in ChemCam data, which also show highly variable MnO. Tentative, but reasonable extrapolation of these data to parts of the Marker Band not visited by the rover suggests an excess Fe mass of 0.2 Gton. Potential processes capable of transporting the metals include transport by chloride-rich brines, or (via interaction with CO) as metal carbonyls. Although post-lithification mechanisms for metal emplacement have not been ruled out, a possible pre-lithification mechanism involves Mn and Fe deposition in a shallow lake in oxidizing conditions. In this scenario, Fe and Mn oxide nodules form and scavenge trace metals (e.g. Zn) by adsorption. We will conclude by discussing remaining open questions about the formation and metal enrichment of the rippled Marker Band. For example, possible sources of water for metal transport include (but are not limited to) compaction water, or alternatively groundwater derived from precipitation inside the crater rim

Metal Enrichment of Wave-Rippled Sediments on Ancient Mars

International audienceThe Curiosity rover is ascending a sedimentary-rock mountain, Mount Sharp, testing hypotheses about how and why Mars' surface dried out. Within the past year, Curiosity has investigated an apparently Mount-Sharp-spanning feature - the Marker Band, which frequently forms a topographic bench. The Marker Band is distinctive in its lateral extent, stratigraphic confinement, and nontrivial thickness. The Marker Band also shows a distinct metal-rich geochemistry unlike any other materials previously analyzed by the rover, and its lower part exhibits wave ripples extending across hundreds of meters (possibly kilometers). Thus, the Marker Band is a marker of a change in the environment within Gale crater from drier conditions that formed underlying sulfates to wetter conditions that formed wave ripples (Gupta et al. this conference). Wave ripples do not persist above the rippled Marker Band, but further clues regarding the evolution of Mars' carbon cycle and atmosphere are obtained from carbonate in drilled samples immediately above the rippled Marker Band (Tutolo et al., this conference), which is strongly elevated in δ13C (Burtt et al., this conference). APXS data for drill fines from ~1 cm depth within the rippled layers show >40 wt% FeO, ~2 wt% Zn, and >1 wt% MnO (Thompson et al., LPSC 2023); metal enrichment is also seen in ChemCam data, which also show highly variable MnO. Tentative, but reasonable extrapolation of these data to parts of the Marker Band not visited by the rover suggests an excess Fe mass of 0.2 Gton. Potential processes capable of transporting the metals include transport by chloride-rich brines, or (via interaction with CO) as metal carbonyls. Although post-lithification mechanisms for metal emplacement have not been ruled out, a possible pre-lithification mechanism involves Mn and Fe deposition in a shallow lake in oxidizing conditions. In this scenario, Fe and Mn oxide nodules form and scavenge trace metals (e.g. Zn) by adsorption. We will conclude by discussing remaining open questions about the formation and metal enrichment of the rippled Marker Band. For example, possible sources of water for metal transport include (but are not limited to) compaction water, or alternatively groundwater derived from precipitation inside the crater rim

Metal Enrichment of Wave-Rippled Sediments on Ancient Mars

International audienceThe Curiosity rover is ascending a sedimentary-rock mountain, Mount Sharp, testing hypotheses about how and why Mars' surface dried out. Within the past year, Curiosity has investigated an apparently Mount-Sharp-spanning feature - the Marker Band, which frequently forms a topographic bench. The Marker Band is distinctive in its lateral extent, stratigraphic confinement, and nontrivial thickness. The Marker Band also shows a distinct metal-rich geochemistry unlike any other materials previously analyzed by the rover, and its lower part exhibits wave ripples extending across hundreds of meters (possibly kilometers). Thus, the Marker Band is a marker of a change in the environment within Gale crater from drier conditions that formed underlying sulfates to wetter conditions that formed wave ripples (Gupta et al. this conference). Wave ripples do not persist above the rippled Marker Band, but further clues regarding the evolution of Mars' carbon cycle and atmosphere are obtained from carbonate in drilled samples immediately above the rippled Marker Band (Tutolo et al., this conference), which is strongly elevated in δ13C (Burtt et al., this conference). APXS data for drill fines from ~1 cm depth within the rippled layers show >40 wt% FeO, ~2 wt% Zn, and >1 wt% MnO (Thompson et al., LPSC 2023); metal enrichment is also seen in ChemCam data, which also show highly variable MnO. Tentative, but reasonable extrapolation of these data to parts of the Marker Band not visited by the rover suggests an excess Fe mass of 0.2 Gton. Potential processes capable of transporting the metals include transport by chloride-rich brines, or (via interaction with CO) as metal carbonyls. Although post-lithification mechanisms for metal emplacement have not been ruled out, a possible pre-lithification mechanism involves Mn and Fe deposition in a shallow lake in oxidizing conditions. In this scenario, Fe and Mn oxide nodules form and scavenge trace metals (e.g. Zn) by adsorption. We will conclude by discussing remaining open questions about the formation and metal enrichment of the rippled Marker Band. For example, possible sources of water for metal transport include (but are not limited to) compaction water, or alternatively groundwater derived from precipitation inside the crater rim

Manganese-Iron Phosphate Nodules at the Groken Site, Gale Crater, Mars

International audienceThe MSL Curiosity rover investigated dark, Mn-P-enriched nodules in shallow lacustrine/fluvial sediments at the Groken site in Glen Torridon, Gale Crater, Mars. Applying all relevant information from the rover, the nodules are interpreted as pseudomorphs after original crystals of vivianite, (Fe 2+ ,Mn 2+) 3 (PO 4) 2 •8H 2 O, that cemented the sediment soon after deposition. The nodules appear to have flat faces and linear boundaries and stand above the surrounding siltstone. Chem-Cam LIBS (laser-induced breakdown spectrometry) shows that the nodules have MnO abundances approximately twenty times those of the surrounding siltstone matrix, contain little CaO, and have SiO 2 and Al 2 O 3 abundances similar to those of the siltstone. A deconvolution of APXS analyses of nodule-bearing targets, interpreted here as representing the nodules' non-silicate components, shows high concentrations of MnO, P 2 O 5 , and FeO and a molar ratio P/Mn = 2. Visible to nearinfrared reflectance of the nodules (by ChemCam passive and Mastcam multispectral) is dark and relatively flat, consistent with a mixture of host siltstone, hematite, and a dark spectrally bland material (like pyrolusite, MnO 2). A drill sample at the site is shown to contain minimal nodule material, implying that analyses by the CheMin and SAM instruments do not constrain the nodules' mineralogy or composition. The fact that the nodules contain P and Mn in a small molar integer ratio, P/Mn = 2, suggests that the nodules contained a stoichiometric Mn-phosphate mineral, in which Fe did (i.e., could) not substitute for Mn. The most likely such minerals are laueite and strunzite, Mn 2+ Fe 3+ 2 (PO 4) 2 (OH) 2 •8H 2 O and-6H 2 O, respectively, which occur on Earth as alteration products of other Mn-bearing phosphates including vivianite. Vivianite is a common primary and diagenetic precipitate from low-oxygen, P-enriched waters. Calculated phase equilibria show Mn-bearing vivianite could be replaced by laueite or strunzite and then by hematite plus pyrolusite as the system became more oxidizing and acidic. These data suggest that the nodules originated as vivianite, forming as euhedral crystals in the sediment, enclosing sediment grains as they grew. After formation, the nodules were oxidized-first to laueite/strunzite yielding the diagnostic P/Mn ratio, and then to hematite plus an undefined Mn oxy-hydroxide (like pyrolusite). The limited occurrence of these Mn-Fe-P nodules, both in space and time (i.e., stratigraphic position), suggests a local control on their origin. By terrestrial analogies, it is possible that the nodules precipitated near a spring or seep of Mn-rich water, generated during alteration of olivine in the underlying sediments

Post-landing major element quantification using SuperCam laser induced breakdown spectroscopy

International audienceThe SuperCam instrument on the Perseverance Mars 2020 rover uses a pulsed 1064 nm laser to ablate targets at a distance and conduct laser induced breakdown spectroscopy (LIBS) by analyzing the light from the resulting plasma. SuperCam LIBS spectra are preprocessed to remove ambient light, noise, and the continuum signal present in LIBS observations. Prior to quantification, spectra are masked to remove noisier spectrometer regions and spectra are normalized to minimize signal fluctuations and effects of target distance. In some cases, the spectra are also standardized or binned prior to quantification. To determine quantitative elemental compositions of diverse geologic materials at Jezero crater, Mars, we use a suite of 1198 laboratory spectra of 334 well-characterized reference samples. The samples were selected to span a wide range of compositions and include typical silicate rocks, pure minerals (e.g., silicates, sulfates, carbonates, oxides), more unusual compositions (e.g., Mn ore and sodalite), and replicates of the sintered SuperCam calibration targets (SCCTs) onboard the rover. For each major element (SiO2, TiO2, Al2O3, FeOT, MgO, CaO, Na2O, K2O), the database was subdivided into five "folds" with similar distributions of the element of interest. One fold was held out as an independent test set, and the remaining four folds were used to optimize multivariate regression models relating the spectrum to the composition. We considered a variety of models, and selected several for further investigation for each element, based primarily on the root mean squared error of prediction (RMSEP) on the test set, when analyzed at 3 m. In cases with several models of comparable performance at 3 m, we incorporated the SCCT performance at different distances to choose the preferred model. Shortly after landing on Mars and collecting initial spectra of geologic targets, we selected one model per element. Subsequently, with additional data from geologic targets, some models were revised to ensure results that are more consistent with geochemical constraints. The calibration discussed here is a snapshot of an ongoing effort to deliver the most accurate chemical compositions with SuperCam LIBS