SIGNIFICANT HALITE ENRICHMENT IN THE SULFATE-UNIT OF GALE CRATER, MARS
Résumé
Since its landing in 2012, the Curiosity rover has been exploring geological records of a paleolacustrine environment in Gale crater. It started with the fluvio-deltaic and lacustrine deposits in the lowermost Bradbury Group, followed by 300 m of stratigraphy through the Murray formation (from the Pahrump Hills to the Jura member) dominated by mudstones and occasionally heterolithic mudstones, siltstones and sandstones. Along this traverse, it also crossed the unconformity with the overlying Stimson formation, dominated by aeolian sandstones, and the Vera Rubin Ridge, an erosion-resistant section of the Murray fm., which has undergone extensive diagenesis [1]. From Sol 2300 to 3072 (Jan. 2019 to Jan. 2021), Curiosity has explored the Glen Torridon region, previously named "Claybearing unit" because of the orbital signatures of clays detected in this area. Since Sol 3100 (Mont Mercou), the rover entered the basal Layered Sulfate unit (also named after orbital observations) with the objective of documenting a possible major change in Mars climate history. Evaporitic salts could represent a geochemical marker of this transition. Here, we provide an overview of previous halite detections by ChemCam [2, 3] and report on new detections made in the sulfate-bearing unit. Data and Method: This study covers data acquired by the ChemCam instrument over the first 3300 sols of the mission and corresponding to ~27800 LIBS analysis points. The detection of halite is made possible by measuring the chlorine emission line at 837.8 nm. Comparing the chlorine peak area to the Na abundance reveals the presence of a group of points showing a strong linear correlation between the two elements (Fig. 1).
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