Characterization and Mapping of Light-toned, Layered Deposits on the Plateaus of Western Valles Marineris with SHARAD and High-Resolution Imagery

Abstract:

Light-toned layered deposits (LLD) are found across the plateaus and near to the rim of Valles Marineris (VM), Mars. The LLD are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and then modified by water, either in lacustrine or fluvial sedimentary deposition. Characterizing the hydrated, layered deposits is essential to testing the hypothesis of their formation and may constrain the timing and duration of water activity in this region. Using instruments onboard the Mars Reconnaissance Orbiter such as HiRISE, CTX, and SHARAD, we mapped the extent of the LLD and other units over the western region of VM. Due to limitations of surface exposure (deposits are buried by dust and dunes), extent could not be fully determined using imagery alone. To remedy this, we employed SHARAD radar sounding data to confirm the presence of LLD and massive deposits in areas where outcrops were unavailable. The flat, high elevation topography of the plateaus are ideal candidates for radar investigations because off-nadir reflections (clutter) does not dominate potential subsurface reflections.

Regions with LLD outcrops are found to have ubiquitous basal reflections. This multi-tooled approach offered a more comprehensive characterization of the region than in previous efforts. The analysis of SHARAD data also opens the door for investigation of the dielectric properties of the LLD, and we find that the bulk permittivity of the materials is ~3, supporting the interpretation of sedimented, low-density ash that has been reworked. We present our now complete radar mapping of the LLD and associated massive (un-layered) deposits that are contiguous with the LLD. We also present morphology maps showing how the units eroded and evolved after formation.

The fully mapped plateaus give larger context to the geology of VM, providing insight into the volcanic history and water cycle some 3.7 Ga before present. This, in turn, will give clues about past climate states on Mars, the timing of Valles Marineris widening, and volcanic activity.