Evidence for the origin of layered deposits in Candor Chasma, Mars, from mineral composition and hydrologic modeling

Abstract

New results from the Compact Reconnaissance Imaging Spectrometer for Mars and High Resolution Imaging Science Experiment and Context Imager cameras on Mars Reconnaissance Orbiter provide insights into the origin of interior layered deposits in Valles Marineris from analysis of a thick, well‐exposed section in western Candor Chasma. Most of the deposit is dominated spectrally by nanophase ferric oxide like that found in the globally distributed eolian dust, with the addition of a prevalent component of monohydrated sulfates. A rippled mantle containing both pyroxene and monohydrated sulfate emanates from discrete layers, which are interpreted as interbedded basaltic sand. Ferric minerals are observed in most of the sulfate‐rich layers, and locally a coarse‐grained grayer component has been concentrated from the layers by sorting. Polyhydrated sulfates are concentrated in discrete layers high in the section, implying chasma‐scale changes in brine chemistry during formation of the layered deposits. Hydrological models were constructed in order to assess whether evaporite deposition from groundwater discharge could have trapped eolian sediments to form the observed deposits. The predicted thickness and extent of the evaporite‐trapped sediment is consistent with the distribution of interior layered deposits in Candor Chasma as well as in other chasmata of Valles Marineris. In this scenario, eolian dust and sand were trapped and lithified by evaporites formed by evaporation of groundwater discharge that was highly localized within the chasmata. Sulfates precipitated in the resulting saline conditions, and diagenetic alteration formed crystalline ferric minerals including hematite. This model links the layered deposits in Valles Marineris and those in Meridiani Planum to a common regional process.