Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44a..09l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44A-09
Physics
3672 Planetary Mineralogy And Petrology (5410), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
The post-chaos layered deposits in Aram Chaos extend laterally approximately 10,000 km2 with a present-day height of ~800 meters above the basement. The deposits experienced significant erosion, in some places down to the basement, indicating a more extensive depositional coverage than evident today. Crystalline hematite, mono- and poly-hydrated sulfate, and pyroxene have been identified in the layered deposits with OMEGA, CRISM, and TES data. Analysis of CRISM targeted observations and CTX images in conjunction with previous work in this region shows a series of layers, listed here stratigraphically from top to bottom: (1) a 250-500m thick, erosionally-resistant cap unit dominated by nano-phase iron oxides, (2) a <500m thick unit with polyhydrated sulfate and hematite signatures, (3) a <50m thick bright-toned unit with 2.1 and 2.4 μm absorptions (best fit by kieserite), and (4) a ~10m thick medium-toned unit with spectra dominated by a 2.23 μm absorption feature, interpreted to be due to a hydrated iron sulfate. The kieserite and candidate iron sulfate layers are visible around the edge of the polyhydrated sulfate/hematite layers, with the iron sulfate occupying the lowest stratigraphic level observable. Both kieserite and candidate iron sulfate layers are unconformably draped over the basement topography, making estimations of actual layer thicknesses difficult; those reported here should be taken as maximum thicknesses. The presence of hematite and hydrated sulfates is evidence that water was involved in the formation of the depositional unit, and variations in the layers indicate that there were temporal changes in the depositional environment. We believe the layered deposits were formed by evaporation of rising groundwater, which would have filtered through and been altered by the chemistry of the basement chaos unit. The sequence of sulfates and hematite overlain by an iron-oxide cap unit mimics the stratigraphy to the southwest in Meridiani Planum, implying similar aqueous histories for the deposits.
Arvidson Ray
Bishop James
CRISM Team
Glotch Timothy
Lichtenberg Kim
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