An Orbital Comparison of a Late Mantling Unit on Aeolis Mons With Other Erosion‐Resistant Strata Explored by MSL in Gale Crater, Mars.

Previous investigations along Curiosity's traverse in Gale crater have explored the relationship between orbital and in situ observations. This work aims to better understand the geologic environment of units only observable from orbit and compare them to the properties of units examined by Curiosity. Here, we map an erosion‐resistant dark‐toned mantling unit that overlies the modern topography of Aeolis Mons (informally known as Mt. Sharp) and compare this unit to two other previously mapped dark‐toned resistant units, the marker band and the mound skirting unit (MSU), that have been inferred to represent different geologic environments (lacustrine and aeolian, respectively). Visible to short wave infrared spectra from the Compact Reconnaissance Imaging Spectrometer for Mars and visual images from the High Resolution Imaging Science Experiment and Context Cameras aboard the Mars Reconnaissance Orbiter are used for this comparison. Spectral data suggest a mafic composition with minor alteration, although the composition varies more with location around Mt. Sharp rather than between units. Morphologically, the mantling unit has strong similarities to the marker band based on their consistent low‐albedo, erosion‐resistance, and smooth appearance, contrasting with the highly variable surface texture of the MSU. We hypothesize that all three units had a similar sediment source but experienced aqueous alteration at different times: early ubiquitous cementation in a surface aqueous environment in the mantling unit and marker band versus patchy late diagenesis in the MSU. If true, these results suggest that water activity continued within the Gale crater long after the erosion of Mt. Sharp. Plain Language Summary: Mars Curiosity rover observations of the physical and chemical properties of rocks are used to characterize past geologic environments in Gale crater. Here, we aim to constrain the properties of geologic units inferred to have formed from past lake and sand dune environments using satellite data sets to see if these same environments can be identified elsewhere on Mars. A newly mapped mantling unit is compared, which overlies (or mantles) rocks in Gale crater, representing deposition later in time. We use compositional data from the Compact Reconnaissance Imaging Spectrometer for Mars and images from the High Resolution Imaging Science Experiment and Context Cameras all aboard the Mars Reconnaissance Orbiter to identify the properties of units in this study. We find that although the mantling unit has a similar composition to both the inferred lake (marker band unit) and sand dune (mound skirting unit) environments, its physical appearance is more similar to the marker band lake environment. This suggests that the mantling unit may represent a water environment and has important implications for understanding the timing of when water was present on Mars. Key Points: A newly mapped mantling unit has surface and spectral features similar to the marker band, both of which differ from the surrounding strataThe mantling unit may represent a similar depositional and/or alteration environment as the marker band but much later in geologic timeThe marker band, mantling unit, and mound skirting unit may have similar sediment sources but different water interactions after deposition [ABSTRACT FROM AUTHOR]