Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21c..02w&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P21C-02
Mathematics
Logic
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We have used predominantly high-resolution images taken by the High Resolution Imaging Science Experiment (HiRISE) camera combined with compositional data from CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) to investigate the geomorphology and formation of light-toned layered deposits (LLDs) within pits and troughs of Noctis Labyrinthus. This region consists of a network of intersecting linear troughs that merge with rounded pits and pit chains before connecting to the continuous troughs of Valles Marineris. We have identified ten pits that have exposures of LLDs and now report on some of the initial findings for two of these deposits. Within one Noctis pit, we have analyzed a light-toned layered deposit with dozens of beds that vary in thickness, brightness, and erosional morphology. These variations are not seen in LLDs in the larger chasmata but we have observed similar lithologies in LLDs along the plateaus of Valles Marineris and within a pit near Juventae Chasma. Exposures of the LLD can only be found where there has been erosion of a capping unit that is dark-toned and blocky, indicating the LLD is relatively older and partially buried. Our CRISM analyses show at least two types of mineralogies in the LLD: (1) a unit spectrally consistent with hydrated Fe-sulfates, such as ferricopiapite, which is found in most of the LLD outcrops, and (2) another bed within the LLD that has a spectrum best matched to the phyllosilicate nontronite. From a HiRISE stereo anaglyph, we have determined that the nontronite-bearing bed occurs within the thicker Fe-sulfate unit but is located towards the lower portion of the LLD strata. Our identification of Fe-sulfates and phyllosilicates within the LLD suggests that significant water once existed within this particular pit. The co-occurrence of phylosilicates and sulfates suggests variable ph conditions, perhaps from influxes of groundwater. The color and brightness heterogeneities seen between individual beds at the meter-scale in HiRISE images cannot be resolved by CRISM but could indicate even more compositional variations than the two major mineralogic units identified spectrally in the LLD. A second pit located north of Oudeman’s crater has a LLD located at several meters depth that is only exposed along the pit’s walls. Because the LLD is only found along the upper walls of the pit, the deposit represents an older unit that could be more extensive at depth. A CRISM spectrum for this LLD is best matched to jarosite, which suggests a distinct LLD mineralogy and morphology compared to the previously mentioned pit. The LLD appears homogeneous throughout the exposed strata, lacking the color, brightness, and mineralogic variations seen in the other LLD. The observation that the LLDs vary morphologically and mineralogically throughout Noctis Labyrinthus suggests that there may be multiple processes with variable amounts of groundwater that are responsible for emplacement and evolution of distinct units in each pit. Our results indicate that transient, isolated and relatively small bodies of water were capable of leading to the accumulation of LLDs in this region.
Bishop Janice L.
Roach Leah
Rodriguez Jose P.
Weitz Catherine M.
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