A chemical model for evaporites on early Mars: Possible sedimentary tracers of the early climate and implications for exploration

摘要: Martian geomorphology seems to indicate extensive hydrological activity during the Noachian era. Liquid water at surface would require a large greenhouse effect that is widely hypothesized have been caused by high partial pressure of atmospheric carbon dioxide, PCO2. A sedimentation model driven sequential evaporation used calculate evaporite mineral sequence in closed basin lake subject The initial fluid derived from weathered igneous rock similar meteorite basalts. Siderite (FeCO3) always first major carbonate precipitate. Thus siderite predicted be an important fades component ancient sediments along with silica, which also early These form varves lakes undergo cycles and recharge. After silica siderite, magnesian calcite, nearly pure hydromagnesite, gypsum, followed highly soluble salts like NaCl. presence generally requires PCO2 level excess ∼0.1 bar, otherwise iron silicates (such as greenalite) form. This may exploration observational test on past composition Mars, consideration depositional environment. At approximately several gypsum precipitation could occur before calcite upon if SO42−:Ca2+ ratio there no consistent recent hypotheses suggesting traces carbonates some meteorites. Several mechanisms destroy or obscure surface. Consequently, situ analysis interior ejecta impact craters lying within sedimentary basins offer most practical approach future sediments.