Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

Abstract

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

Low Hesperian P CO2 constrained from in situ mineralogical analysis at Gale Crater, Mars

“…2). We have no direct constraints on the rates of deposition of the YKB formation, but given the similarity of the sedimentary architecture with terrestrial fluvial-lacustrine deposits (8) we use compilations of thousands of lacustrine accumulation rates observed on Earth to obtain an upper limit for the YKB formation (31). Terrestrial lacustrine sedimentation rates span several orders of magnitude, with a dependence on the time span of accumulation (32).…”

“…Upper model boundary conditions are set to simulate a well-mixed lake in equilibrium with an assigned P CO2 atmosphere. This is a valid representation given the absence of glaciogenic sedimentary features, such as dropstones, ice wedges, and glacial tills, in Gale lake deposits that would indicate ice cover, and the meter-scale thicknesses of delta deposits that indicate water depths of the same order (8).…”

“…Here we take a step beyond assuming mineral equilibrium and combine estimated sedimentation rates, afforded by detailed sedimentary facies analysis (8,12), with carbonate precipitation kinetics and observed mineralogy to estimate ancient P CO2 using a geochemical reaction-transport model.…”

Mineral paragenesis on Mars: The roles of reactive surface area and diffusion

“…The kilometer‐thick sedimentary sequence observed in the central mound of Gale crater, which beautifully displays the transition from ancient clay sediments to more recent sulfate and oxide assemblages [ Milliken et al ., 2010, 2014], may serve as a test site for our hypothesis presented here: the clay sediments would have been deposited in ancient lakes covering the crater floor [ Grotzinger et al ., 2015]; time after, new interactions between water and the central mound of the crater [ Fairén et al ., 2014] would have resulted in the precipitation of sulfates. This is consistent with the observed transition in sulfate occurrences at Gale: from postdepositional Ca‐sulfate veins ubiquitous in almost all of the clay‐rich bedrock in the crater floor up to the Murray Buttes [ Nachon et al ., 2014], to abundant Ca‐sulfate cemented sandstones at the Murray Buttes [ Newsom et al ., 2017], suggesting a possible change in the original mode of deposition that may be interpreted within the framework of the processes modeled in this paper.…”

“…Indeed, subsequent interactions between water and the central mound could have remobilized/reactivated older deposits. Upcoming data from the Curiosity rover will be useful to test our model results, as the rover exploration has already provided direct evidence for different lakes coming and going over Gale crater during up to tens of millions of years [ Grotzinger et al ., 2015; Hurowitz et al ., 2017]. …”