Biology
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53b1446w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53B-1446
Biology
5410 Composition (1060, 3672), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
From orbit, phyllosilicates and hydrated sulfates on Mars have typically been observed in distinct geographic locales and are thought to record different types of ancient aqueous environments [1]. However, these two mineral classes have recently been found in close association in each of two large impact craters in the Terra Sirenum region of the Southern highlands [2, 3]. In one of these, the D~100 km crater Columbus, CRISM observations show that a polyhydrated non-Fe sulfate is the spatially dominant phase, whereas other distinct layers have spectra consistent with the iron sulfates jarosite and szomolnokite, respectively. Another distinct spectral unit may contain hydrated chloride, or a different non-Fe sulfate. A kaolin group clay is the most commonly detected phyllosilicate, occurring in all CRISM scenes that show the polyhydrated sulfate, but Fe/Mg-phyllosilicates are also seen in small exposures. The polyhydrated sulfate occurs in a light-toned, finely layered, indurated deposit that extends around ~270 degrees of the inner crater wall. The kaolinite unit is commonly stratigraphically beneath the polyhydrated sulfate unit, but some interbedding of the two materials is tentatively observed. Hydrated materials are also present in strata exposed on the crater floor. Kaolinite, sulfates, and chlorides are observed precipitating out of terrestrial acid-saline lakes and ground waters [4], which may be analogs for the environment that deposited the materials in Columbus crater. The overall structure of the deposit is reminiscent of terrestrial "bathtub ring" evaporite deposits. Alternatively, the exposed ring could be part of a preexisting subsurface layer exposed by the impact event; however, the mineral assemblage seen here (kaolinite and polyhydrated sulfate) has not yet been observed in any other craters or intercrater bedrock exposures in the region. Further imaging and topographic data will be used to test the evaporite hypothesis by carefully examining the stratigraphic relationship between the hydrated deposits and crater wall slump blocks. The acidity and salinity implied by the observed mineral assemblage would have posed significant challenges to Martian life here, but fossils preserved in terrestrial acid-saline lake evaporites [5] suggest that sediments in Columbus may also be capable of preserving potential biosignatures until the present day. [1] Bibring, J.-P., et al. (2006), Science 312, 400-404. [2] Wray, J. J., et al. (2008), DPS 40, #03.04. [3] Swayze, G. A., et al. (2008), this conference. [4] Benison, K. C., et al. (2007), J. Sed. Res. 77, 366-388. [5] Benison, K. C., et al. (2008), Astrobiology, in press.
Dundas Colin Morrisey
Milliken Ralph E.
Murchie Scott L.
Seelos Frank P.
Squyres Steve W.
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