MINERALOGY AND STRATIGRAPHY OF THE GALE CRATER RIM, WALL, AND FLOOR UNITS FROM REMOTE SENSING

Mt. Sharp and the units explored by Curiosity on the Gale crater floor record a succession of lacustrine, fluvial, and aeolian environments, recording changes in the surface habitability of Mars. Yet, the origins and history of these units are not yet fully understood. Here, we examine the mineralogy and stratigraphy of Gale crater’s rim/wall bedrock and floor to understand the provenance and history of these transported materials. We analyzed imagery from CTX and HiRISE and visible/infrared spectra from CRISM and THEMIS. No significant differences in unit spectral properties were observed with THEMIS, and the majority of CRISM scenes were homogenous, spectrally bland, and/or noisy. Those CRISM scenes that did reveal mineralogy showed a sometimes olivine-bearing bedrock often accompanied by Fe/Mg phyllosilicates and other hydrated phases. Bedrock on the eastern Gale rim also includes a hydrated phase with a 2.48-µm absorption. Several sedimentary strata on the NW Gale floor, SW of the landing site also have Fe/Mg phyllosilicates. They are likely comprised of significant quantities of detrital material sourced from the rim/wall and are likely coeval with the Bradbury unit explored by MSL. The spectral properties of the Fe/Mg phyllosilicates along the walls and floor differ from the Al-substituted nontronite detected by Milliken et al. (2010) on Mt. Sharp, suggesting formation in aqueous environments of different water chemistry. The eastern Gale rim hydrated mineral detections are spectrally similar to the sulfate unit in Mt. Sharp detected by Fraeman et al. (2016), which indicates the units may have formed from or been altered by waters of similar chemistry. Our geologic mapping of the NW Gale crater floor shows multiple instances of hydrated/hydroxylated minerals overlain by spectrally undistinctive, more erosionally resistant units, likely aeolian sandstones. A crater on the northern floor exposes >300 m of sedimentary stratigraphy, including thinly layered units at its lowest extent. These data indicate substantial sedimentary infill of Gale. The lowermost thin layers are consistent with a lacustrine environment. Interbedded units of different hydrated/hydroxylation overlain by an aeolian sandstone point to changing environmental conditions perhaps in a drying, or alternately dry lake bed.