Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p32a..02m&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P32A-02
Mathematics
Logic
[6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The mound centered in Gale Crater, Mars hosts a 5 km thick sequence of gently dipping strata whose morphological properties are largely consistent with a sedimentary origin and whose visible-near infrared reflectance spectra exhibit signatures consistent with Fe-rich clay minerals, sulfate salts (mono- and polyhydrated varieties), and red hematite. CRISM reflectance spectra reveal that the lower tens of meters of the mound contain sulfate salts, likely Mg-varieties, that are overlain by thinner beds of Fe-smectite (nontronite) bearing sediments. In some locations these clay beds appear to lack sulfate signatures, but in others they have spectral properties consistent with both clays and sulfates, indicating these phases are either interbedded at a scale below the 18 meter per pixel spatial resolution of CRISM data or that they are intimately mixed. The strata immediately above the Fe-smectite beds exhibit spectral signatures indicative of hydrous phase(s) of indeterminate composition and origin, though possible spectral matches based on laboratory experiments include leached smectites or poorly crystalline sulfate-clay mixtures formed at circum-neutral pH. In some locations these deposits also contain red hematite (non-nanophase hematite that is distinct from Martian dust). The strata overlying these units are dominated by sulfates, including kieserite and polyhydrated sulfates (likely Mg-varieties such as hexahydrite). The sulfate-bearing units often contain pyroxene, and the lower portion of the mound is unconformably overlain by a pyroxene-bearing cap unit that extends around the mound and onto the floor of Gale Crater. In contrast to the diverse mineralogy found in the lower half of the mound, the upper portion exhibits meter-scale strata of regular thickness whose spectral signatures are similar to ubiquitous Martian dust. This could indicate that these units are mantled by a thin layer of dust or that the beds themselves are composed of weakly lithified dust. If the latter, these beds may be the result of orbital forcing and thus record recent climatic changes, as has been suggested for other sequences that exhibit rhythmic bedding on Mars. As a whole, the mineralogy of the mound in Gale Crater may record the 'drying out' of Mars as one traverses upsection. The lower mound records a transition from clay-sulfate to net sulfate accumulation/formation upsection, and these deposits are overlain by apparently anhydrous phases similar to Martian dust. The origins of the strata as well as the specific formation mechanisms for the hydrous minerals they host remains enigmatic, but the diversity present in Gale Crater provides a wealth of opportunity for the MSL payload to explore habitability and aqueous processes on ancient Mars in a sedimentary sequence that likely records multiple depositional environments.
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