A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

Abstract

Abstract. The Curiosity rover discovered fine--grained sedimentary rocks, inferred to represent an ancient lake, preserve evidence of an environment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference N and P are assumed to have been available. The environment likely had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial--lacustrine environments in the post--Noachian history of Mars.

Low HesperianPCO2constrained from in situ mineralogical analysis at Gale Crater, Mars

“…In drawing the stability boundaries for magnetite, redox state is set at the magnetite/hematite boundary, as detailed in the main text. All thermodynamic data come from the Lawrence Livermore National Laboratory dataset (15) matrix and the lack of detection of evaporative minerals in the mudstone (9,11,12). This is compatible with bulk geochemical evidence of limited chemical alteration of sediments during erosion and transport from the source area (11).…”

“…Terrestrial lacustrine sedimentation rates span several orders of magnitude, with a dependence on the time span of accumulation (32). With accumulation times of 100s to 10,000 y estimated for the 1.5-m-thick Sheepbed member (12), accumulation rates as high as 5 cm/y are possible, with an average rate ∼0.1 cm/y (32). Lacustrine deposits with sedimentation rates >1cm/y make up <1% of available records.…”

“…This reinforces our estimates that the martian atmosphere contained 10s mbar levels at the time of deposition of YKB sediments. Fluvial-lacustrine sediments in Gale Crater represent one of the youngest known instances of habitable surficial aqueous conditions on Mars, on the tail end of a period of rapid atmospheric degradation and loss (6,12,33). Thus, our P CO2 estimate serves as a reference point at a critical juncture in martian atmospheric evolution.…”

“…It is proposed that isochemical alteration during the deposition of lacustrine mudstone at YKB involved dissolution of Fe 2+ -bearing olivine (Fo 62 ) providing a source of Fe 2+ and Mg 2+ in pore waters for subsequent coeval precipitation of magnetite and Fe 2+ -bearing, ferrian saponitetype clay minerals (9,(11)(12)(13)(14). The detection of these secondary phases indicates anoxic to poorly oxidizing conditions (13), and places lower limits on the pore water activity of Fe 2+ and Mg 2+ released from olivine.…”

“…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.…”