Analyses of Sulfate Deposits in the Martian Equatorial Chaos Regions

We are conducting a coordinated effort to investigate the sulfate-bearing deposits within several different chaos terrains on Mars, including Aram Chaos, Iani Chaos, Aureum Chaos, Aurorae Chaos, and Arsinoes Chaos. Previous studies focused on sulfate deposits at three locations within the equatorial chaos regions were all conducted prior to 2014 using different data sets [1-8]. Improved CRISM image processing using Map-Projected Targeted Reduced Data Record (MTRDR) images [9] have enabled more precise identification and discrimination of sulfates, as well as the acquisition of numerous additional CTX, HRSC, and HiRISE images that provide additional coverage of the morphologies and locations of sulfates within the equatorial chaos regions. We also used the lower resolution but larger spatial coverage of the CRISM mapping data to produce indicator vector maps [10] across the chaos region which allowed us to identify polyhydrated (PHS) and monohydrated (MHS) sulfate outcrops in between locations of targeted CRISM images. Orbital data that we are analyzing include: CRISM MTRDR images and mapping-data-derived mineral indicator GIS vectors specific to the sulfates; HiRISE images and derived Digital Terrain Models (DTMs); CTX images and mosaics; and HRSC images and DTMs.

HiRISE and CTX images that cover the chaos regions were used to identify deposits that are generally brighter and smoother relative to the darker, hilly chaos terrain in which they occur. We mapped out the distribution of these light-toned deposits (LTDs) in ArcPro and determined they are more extensive than previously mapped. CRISM images were analyzed of the LTDs using spectral parameter maps corresponding to diagnostic mineralogies which indicate the presence of different types of sulfates. We identified sulfate-bearing units at all five chaos regions in association with the larger LTDs, with signatures of polyhydrated and monohydrated sulfates. At Aram Chaos, we identified ferric hydroxysulfate outcrops (FHS; Fe³⁺SO₄OH) beyond what was mapped previously.

There are both similarities and differences between the sulfates within the chaos regions. Similarities include the identification of PHS at all five chaos locations and MHS at four, with stratigraphic relationships showing the PHS are always above the MHS where they occur together. Differences include variations in the brightness and surface textures of each type of sulfate. By comparing the distribution, mineralogy, stratigraphy, and morphology of the sulfates within each of the five chaos regions, we hope to evaluate how the geologic setting of each chaos region may have affected the characteristics of each sulfate deposit that formed within it. 

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