Banding in Mount Sharp, Gale Crater: Stratigraphy, Strandlines, or Buttress Unconformities?

Abstract:

Banding along the lower flanks of Mount Sharp has generally been interpreted to indicate stratigraphy within the mound that dips gently outward from it. Many of these bands define prominent terraces that can be traced nearly to closure around the mound, potentially providing chronostratigraphic markers. However, comparing orbital imagery and digital elevation models with ground-based views from Curiosity’s Mastcam suggests much of the banding might indicate buttress unconformities of now-largely-deflated plains units and/or paleolake strandlines that may not extend into the subsurface. Resistant horizons that parallel the upper surface of the mound can be identified in several erosional pits and along flanks of many of the butte “foothills” of Mt Sharp. These surfaces suggest that Mt Sharp was emplaced as a mound that may have been a few percent larger than the modern remnant, but that likely never extended across Gale crater and over the surrounding highland terrains.

Other geomorphic surfaces – e.g., the fan-shaped feature at the mouth of the science target canyon – suggest paleo stratigraphic surfaces that dip outward at an angle steeper than the banding. The banding continues across these resistant horizons and other geomorphic surfaces without interruption, supporting the inference that it is overprinted onto dipping stratigraphy within Mt Sharp. Previously, we have identified at least three lake levels associated with major valley network fans/deltas debouching into Gale through the crater’s rim. It may be possible to correlate these with specific bands or terraces along the outer margin of Mount Sharp, enabling volume estimates and relative timing of lake levels within the crater to be addressed.