Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44a..02m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44A-02
Mathematics
Logic
5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 5464 Remote Sensing, 5470 Surface Materials And Properties, 5494 Instruments And Techniques
Scientific paper
Results from CRISM, HiRISE, and CTX on MRO provide new insights into the origin of interior layered deposits (ILDs) in Valles Marineris. A well-exposed, thick sequence in western Candor Chasma has spectral properties consistent with basaltic sand mixed with nanophase iron oxide-rich dust, with the addition of sulfates and crystalline ferric oxides. Most of the deposit is dominated spectrally by the dust component. Monohydrated and polyhydrated sulfates are concentrated in separate, interbedded layers, which in some cases are traceable over tens of kilometers. Monhydrated sulfates dominate the lower part of the deposits whereas polyhydrated sulfates are more common in upper strata. The deposits are partially mantled by low- albedo eolian ripples that contain pyroxenes similar in composition to what is found on the surrounding plateau, plus sulfates predominantly in monohydrated form. The dark ripples originate from discrete, friable layers. Similar dark, erodible layers elsewhere on Mars have been interpreted as buried eolian sand. Crystalline ferric oxides are concentrated in the sulfate-rich layers, and mass wasting has accumulated them at the base of steep slopes to form the deposits of gray hematite detected by TES. The persistence of monohydrated sulfates in debris shows that alteration of monohydrated to polyhydrated sulfates, proposed as an important weathering process, takes long compared to formation of the thin layer that dominates reflectance properties. The observed stratification of sulfate compositions implies differences in the abundance of liquid water or brine chemistry during deposition or early chemical modification of sediments. Inferred mineralogy and compositional stratification are similar to what is observed in sulfate-rich sediments in the Meridiani and Aram Chaos regions. The Meridiani deposits were proposed to accumulate where evaporites formed in areas of groundwater discharge and cemented eolian sediments, in which coarse- grained hematite formed by diagenetic alteration. Modeling of the history of groundwater discharge in Valles Marineris shows that thick evaporite sequences are also expected within the chasmata, and could have similarly trapped eolian sediments. Areas with predicted thick accumulations enclose the major eroded remnants of the ILDs. Formation of the ILDs by lithification of eolian sediment by evaporites in areas of groundwater discharge links the spectrally and morphologically similar, sulfate- and ferric-oxide bearing deposits in Valles Marineris, Aram Chaos, and Meridiani to a common regional process.
Andrews-Hanna Jeffrey
Arvidson Ray
Bibring J.
Bishop James
Lichtenberg Kim
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