Sequence and relative timing of large lakes in Gale crater (Mars) after the formation of Mount Sharp

Abstract

The quantification of lake levels in Gale crater is important to define the hydrologic and climatic history experienced by the sedimentary deposits found by Curiosity. We propose that there were at least three major lake stands within Gale, each persisted >1000 years, and all occurred after Mount Sharp reached close to its current topographic form. Deltaic deposits off the southern rim of Gale, derived from incision of Farah Vallis, and corresponding deposits off the southern flank of Mount Sharp define the highest lake level, which had a mean depth of 700 m. Canyons similar in form to Farah Vallis enter into craters and/or the crustal dichotomy near Gale from the south, suggesting that the highest lake was supplied by a large‐scale flow system. The next lake level, established after a period of drying and rewetting, is defined by four deltaic features, three sourced from Mount Sharp and one from the western rim of Gale, as well as the termination of gullies around the northern rim of Gale. This second lake level had a mean depth of 300 m. The presence of the gullies suggests more locally sourced water. Lake levels then rose another 100 m, as evidenced by two deltaic deposits derived from the rim of Gale and the termination of a second set of gullies. Post‐lake, reduced hydrologic activity continued, evidenced by a time of fan building (including Peace Vallis). The sequence of events suggests an episodic shift through time from relatively wet regional conditions to a drier environment with local runoff.

Reconstructing the past climate at Gale crater, Mars, from hydrological modeling of late‐stage lakes

“…A transition to sustained arid conditions is then required to explain the evaporitic sulfate cementation of aeolian sediments found at higher elevations in the mound [Milliken et al, 2010;Thomson et al, 2011], similar to the sulfate deposits found by the Mars Exploration Rover Opportunity at Meridiani Planum [Grotzinger et al, 2005;McLennan et al, 2005;Squyres and Knoll, 2005;Arvidson et al, 2006Arvidson et al, , 2014 and elsewhere on Mars [Bibring et al, 2006;Glotch and Rogers, 2007;Murchie et al, 2009;Zabrusky et al, 2012]. Thus, although evidence supports increasingly arid conditions on Mars during the transition from the Noachian through Hesperian, the climate was clearly variable on shorter timescales with returns to Noachian-like conditions for sufficiently long periods of time to produce the observed deltas and associated late-stage lakes [Palucis et al, 2016]. Finally, the results of this work indicate a return to semiarid conditions at some point during the Hesperian or later in order to produce the late-stage Gale crater lakes.…”

“…Decreasing the annual precipitation for a given aridity index (and thus decreasing the evaporation potential proportionally) results in a proportional decrease in aquifer recharge. The horizontal dashed lines are the lake stands inferred by Palucis et al [2016] and correspond to the colored contours in Figure 1, while the vertical lines delineate climate zones. In other words, at lower precipitation rates Gale captures more of the regional groundwater flow and the Gale lakes are stable at higher aridity indices.…”

“…Based on the observed elevations of deltas and fans, these lake stands were estimated to fluctuate between À3280 m elevation (followed by a desiccation period), À3980 m, and À3780 m. These lakes were likely active during the Hesperian, though an Amazonian age cannot be ruled out [Palucis et al, 2016]. The large extent of these fan deposits suggests that these lakes persisted for 10,000 to 100,000 years depending on assumed discharge rates in the surrounding catchments and a rock to water ratio of 0.0001 [Palucis et al, 2016].…”

“…We use hydrological models of Gale crater lake to constrain a range of post-Aeolis Mons climates compatible with the lake stands inferred by Palucis et al [2016] and open-and closed-basin lakes outside of Gale crater [Cabrol and Grin, 1999;Fassett and Head, 2008;Goudge et al, 2012Goudge et al, , 2015. Lake levels are a product of the complicated interplay of the surface and subsurface components of the hydrological cycle, which in turn are driven by the climate and the topography of a basin and its watershed.…”

Geological Evidence of Planet‐Wide Groundwater System on Mars

“…These features are likely to have resulted from a process of groundwater upwelling followed by water table fluctuations and eventual groundwater recession. The presence of a large number of water‐formed features in all these deep basins (Figure ) is a compelling sign that Mars once had large amounts of water stored as groundwater that debouched into the intercepting craters to form lacustrine systems (Palucis et al, ). The purpose of this work is to identify these water‐related features at a basin level, define their depositional environments and then analyze them holistically at a planetary scale to identify whether they are the result of a single planet‐wide control (Figure ).…”