Stratigraphy of Hydrated Sulfate Layers in Aram Chaos, Mars: Implications for Multiple Hydrologic Events

Near-infrared spectroscopic data can provide information on the type (monohydrated vs. polyhydrated) and locations of hydrated sulfate deposits on Mars. One particular deposit, in Aram Chaos, has been well-studied and shows widespread deposits of both mono- and polyhydrated sulfates in OMEGA data and gray crystalline hematite in TES data. Both sulfates and hematite are located in eroded and exposed sections of a unit emplaced after the initial chaos-forming event. Further examination of this region by Noe Dobrea et al (2008) shows that the locations of the polyhydrated sulfates and hematite overlap and do not coincide with locations of the monohydrated sulfate; this, along with a visible layered structure in the eroded unit suggests that there were either multiple depositional events or multiple post-depositional alterations of the emplaced unit. The advent of data from the CRISM (~20 meters/pixel), CTX (~6 meters/pixel), and HiRISE (~35cm/pixel) instruments enables a closer look at the stratigraphy and mineral content of the exposed layering in Aram Chaos. Specifically, this project uses CRISM data to look at the variations in hydrated sulfate signatures associated with fine (~100m) layering and CTX, HRSC, and HiRISE data to establish the fine-scale stratigraphic order of layers. We find in some areas where multiple layers are exposed and only moderately covered by aeolian sands that the sulfate signature decreases with increasing height in stratigraphic column. In other areas, the strongest sulfate signature is associated with terrace edges where the emplaced unit embays the original chaos-forming (and non-sulfate-bearing) unit. The sulfate- and hematite-bearing units all occur stratigraphically beneath a cap unit dominated spectrally by iron oxides. The relation of the sulfate- and hematite-bearing units to the thicker cap unit mimics the stratigraphy in Meridiani Planum, implying that these two areas experienced similar hydrological histories despite the purported age difference between the two.