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Martha S. Gilmore, James P. Greenwood, Peter C. Patton


Earth and Environmental Sciences




A ~60km diameter crater within Eridania Basin, Terra Sirenum, Mars, contains bright, friable, and layered rocks with mineral spectra akin to the iron-carbonates ankerite and siderite. These minerals associate with gullies and modified regions along the crater’s northeastern extent. Mixtures between the carbonates and select tectosilicate, phyllosilicate, and inosilicate minerals may account for shallow 2.5μm absorptions and shifted inter-absorption features between the 2.3μm and 2.5μm absorptions within the crater spectra. Broad and shallow 1.0μm features may be caused by the carbonates and/or the silicate mineral mixtures; the presence of wollastonite may also be a contributing factor. Spectral discrepancies are not explained by the presence of olivine. High calcium-pyroxene minerals, possibly augite, occur along the crater’s central and wall features, and are potentially mixtures with small amounts of forsteritic olivine. It is believed that the carbonates stem from outcrops within the upper elevations of the crater’s rim. Related talus and boulders coat the lower elevations and are contained within channels and depositional fans. The postulated formation scenario suggests that the carbonates were primarily emplaced within sedimentary deposits and may have been exposed to aqueous environments. The carbonates experienced subsequent low-temperature and pressure metamorphism, burial diagenesis, and/or hydrothermal alteration. Both carbonates could have developed within superimposing or juxtaposing layers. Siderite may have altered to other minerals and/or failed to subsist after exposure to Martian conditions due to its lesser stability. Volcanic flows may have aided in carbonate and/or silicate formation, and later gully evolution exposed the outcrops. The carbonates are believed to be Noachian in age and are consistent with carbonates that have been found elsewhere on Mars.



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