Mineralogy and stratigraphy of the Gale crater rim, wall, and floor units

Abstract

The Curiosity rover has detected diverse lithologies in float rocks and sedimentary units on the Gale crater floor, interpreted to have been transported from the rim. To understand their provenance, we examine the mineralogy and geology of Gale's rim, walls, and floor, using high‐resolution imagery and infrared spectra. While no significant differences in bedrock spectral properties were observed within most Thermal Emission Imaging System and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) scenes, some CRISM scenes of rim and wall rocks showed olivine‐bearing bedrock accompanied by Fe/Mg phyllosilicates. Hydrated materials with 2.48 μm absorptions in Gale's eastern walls are spectrally similar to the sulfate unit in Mount Sharp (Aeolis Mons). Sedimentary strata on the Gale floor southwest of the landing site, likely coeval with the Bradbury units explored by Curiosity, also are hydrated and/or have Fe/Mg phyllosilicates. Spectral properties of these phyllosilicates differ from the Al‐substituted nontronite detected by CRISM in Mount Sharp, suggesting formation by fluids of different composition. Geologic mapping of the crater floor shows that the hydrated or hydroxylated materials are typically overlain by spectrally undistinctive, erosionally resistant, cliff‐forming units. Additionally, a 4 km impact crater exposes >250 m of the Gale floor, including finely layered units. No basement rocks are exposed, thus indicating sedimentary deposits ≥250 m beneath strata studied by Curiosity. Collectively, the data indicate substantial sedimentary infill of Gale crater, including some materials derived from the crater rim. Lowermost thin layers are consistent with deposition in a lacustrine environment; interbedded hydrated/hydroxylated units may signify changing environmental conditions, perhaps in a drying or episodically dry lake bed.

The Mars Science Laboratory (MSL) Bagnold Dunes Campaign, Phase I: Overview and introduction to the special issue

“…Reworking of the nearby Stimson sandstone is possible as the elemental chemistries are similar, but the Stimson has little to no olivine in contrast to the dunes. Thus, this suggests that the origin of the dunes is erosion of the olivine‐bearing walls of Gale crater [ Buz et al ., ] and/or erosion of sandstones yet‐to‐be‐encountered on the rover's ascent of Mount Sharp [ Ehlmann et al ., ].…”

“…and (ii) how does Martian sand mineralogy and volatile content vary with grain size? Lastly, orbital (and later in situ) data showed aeolian sandstone units in Mount Sharp and on the Gale crater floor [ Anderson and Bell , ; Milliken et al ., ; ; Le Deit et al ., ; Buz et al ., ]. Investigation of modern Martian sand dunes offered an opportunity to examine the structures and chemistry of aeolian sediments prior to lithification and diagenesis.…”

Chemistry, mineralogy, and grain properties at Namib and High dunes, Bagnold dune field, Gale crater, Mars: A synthesis of Curiosity rover observations

“…However, in contrast to Gobabeb sands, the Stimson sandstones contain no olivine above the 1-2 wt % threshold of CheMin detection [Yen et al, 2017]. There is no modern evidence for regional sands blowing into Gale, so sand-sized grains eroded from the olivine-bearing Gale walls [e.g., Ehlmann and Buz, 2015;Buz et al, 2017], sandstones exposed elsewhere on the Gale floor [e.g., Buz et al, 2017], or sandstone strata further up Mount Sharp than the rover has traversed [e.g., Le Deit et al, 2013] are the most likely sources of mafics.…”

Extensive Polygonal Fracture Network in Siccar Point group Strata: Fracture Mechanisms and Implications for Fluid Circulation in Gale Crater, Mars

“…The SPg occupies a topographic depression in northwest Gale crater, where it bridges the contact between strata of the Bradbury and Mount Sharp groups (Grotzinger et al, ) and is preserved at higher elevations as the fan‐shaped Greenheugh pediment at the base of a prominent valley (Gediz Vallis) that originates at the unconformity that separates strata of lower and upper Mount Sharp (Milliken et al, ). Strata associated with the SPg have previously been referred to as the “mound skirting” unit (Anderson & Bell, ), the “lower mound marginal” unit (Thomson et al, ), the “washboard” unit (Buz et al, ; Kah et al, ; Milliken et al, ; Rubin et al, ), the “crater floor” unit (Le Deit et al, ), and the “high thermal inertia” unit (Fraeman et al, ). The range of potential depositional environments represented by SPg strata is uncertain (cf.…”