Mars Science Laboratory Observations of Chloride Salts in Gale Crater, Mars

The Mars Science Laboratory Curiosity rover is traversing a sequence of stratified sedimentary rocks in Gale crater that contain varied eolian, fluviodeltaic, and lake deposits, with phyllosilicates, iron oxides, and sulfate salts. Here, we report the chloride salt distribution along the rover traverse. Chlorine is detected at low levels (<3 wt.%) in soil and rock targets with multiple MSL instruments. Isolated fine-scale observations of high chlorine (up to >= 15 wt.% Cl), detected using the ChemCam instrument, are associated with elevated Na2O and interpreted as halite grains or cements in bedrock. Halite is also interpreted at the margins of veins and in nodular, altered textures. We have not detected halite in obvious evaporitic layers. Instead, its scattered distribution indicates that chlorides emplaced earlier in particular members of the Murray formation were remobilized and reprecipitated by later groundwaters within Murray formation mudstones and in diagenetic veins and nodules. Plain Language Summary Chlorine is measured in soils and rocks in Gale crater by multiple instruments on the Mars Science Laboratory Curiosity rover. Fine-scale points of enriched chlorine are detected by the ChemCam instrument in bedrock, nodules, and at the margins of veins in the Murray formation. Chlorine content is correlated with weight percent Na2O indicating halite composition, corroborated by CheMin and SAM data. The scattered distribution of chlorides in the Murray formation indicates they were dissolved by later groundwaters then recrystallized. The chlorides may have been emplaced as small-scale primary deposits in particular members of the Murray formation, consistent with varying salinity in the waters that deposited the Murray.