Geomorphic constraints on a regionally extensive groundwater system in the Gale Crater region

Abstract:

Gale crater, home of the Curiosity rover, contains some of the best geomorphic and sedimentologic evidence on Mars for large lakes and surface runoff during the Hesperian. Orbital data and rover observations, including inferred delta deposits and the terminations of gully networks, suggest several phases of stable lake levels after the deposition and erosion of the sedimentary mound (informally referred to as Mt. Sharp) within Gale. However, the regional extent, water source (i.e., groundwater versus surface water, precipitation versus snowmelt), and climate during each lake stand is still debated.

In order to test whether Gale was hydrologically integrated within a regional lake system via an extensive groundwater table (versus a closed system maintained by precipitation and surface runoff), we performed detailed geomorphic mapping in combination with hydrologic modeling in the region directly upslope of Gale crater. We mapped small-scale gully networks and their terminations within craters without inlet/outlet channels and assessed the potential of using gully terminations as indicators of former lake stands. We then compared our inferred paleo-lake levels with results from a combined groundwater-surface water hydrologic model for several different climate scenarios. To assess the timing of lake stability within the region, we used standard crater counting techniques.

Consistent elevations of gully network terminations within seventeen craters upslope of Gale crater likely record paleo-lake levels. Hydrologic modeling indicates Gale was integrated within the regional subsurface hydrology, and paleo-lake levels record a regional drying trend from sub-humid to semiarid conditions. Crater counting indicates the persistence of surface water until at least 3.2 Ga. This work has implications for understanding water source and chemistry affecting sediments investigated by Curiosity.