¹Ivy Ettenborough, ¹Anna Szynkiewicz
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.116384]
¹Department of Earth and Planetary Sciences, University of Tennessee, 1621 Cumberland Ave., Knoxville, TN 37996, USA
Copyright Elsevier

Secondary sulfate minerals are common throughout the sedimentary deposits of Mount Sharp, located within Gale crater on Mars. However, the source of sulfate (SO42−) and past climatic conditions during their formation are not well understood. Therefore, we investigated the δ34S, δ18O, and δ2H of gypsum veins and other Mg- and Ca- sulfates forming as salt crusts and cement within the shallow sediments of the Rio Puerco watershed in central New Mexico. The δ34S values of vein gypsum and acid-soluble SO42− (cement) varied over the same range (₋33.3 to ₋12.9 ‰ and ₋34.6 to ₋12.1 ‰, respectively), which was similar to the δ34S of bedrock sulfide minerals (₋37.4 to ₋5.9 ‰). This implies that sulfide oxidation is the main source of SO42− in the Rio Puerco aqueous system. The measured δ18O values of SO42− (₋8.9 to +3.1 ‰) as well as δ18O and δ2H values of gypsum hydration water (₋8.9 to +0.6 ‰, and ₋112 to ₋82 ‰, respectively) overlapped with the isotope composition of local meteoric precipitation, suggesting that sulfide oxidation to SO42− and gypsum formation have occurred under semi-arid climate conditions. The isotope results suggest the top-down infiltration of meteoric water leads to leaching of SO42−, Mg+, and Ca2+ from bedrock sulfide weathering followed by abundant formation of Mg- and Ca-sulfates in surface deposits and gypsum veins with depth. Because of spatial and mineralogical similarities in the secondary Mg- and Ca-sulfate mineral occurrences, we hypothesize that chemical weathering of sulfide minerals could have been the main source of SO42− in the aqueous system of Gale crater.