Using Color to Map Diagenesis in Gale Crater: Comparing the Rover and Orbital Perspective

NASAs Curiosity rover has found evidence of diagenesis at a variety of scales, but their extent in Gale crater is poorly constrained. Some color variations visible from both the ground and orbit indicate differences in, likely diagenetic, secondary minerals. We hypothesize that late diagenesis was primarily driven by differences in permeability influencing fluid flow, due to variations in phyllosilicate content, grain size, and cementation. In this study, we use orbital color and mineralogical data to test this by mapping large color and spectral variations across Mt. Sharp and assessing evidence of diagenesis. A better understanding of the distribution of altered units across Mt. Sharp will allow us to better assess how representative rover observations of diagenesis in the Murray formation are of broader Gale. Some large-scale color variations in Gale have been attributed to late diagenetic alteration, including bright features visible from HiRISE on the Vera Rubin ridge. Curiosity data showed these bright features corresponded to gray patches containing coarse gray hematite, likely formed by diagenetic fluids. This suggests that late diagenesis could be identified elsewhere in Gale using stretched HiRISE color images. We use HiRISE for qualitative analysis only due to a ~20% uncertainty on radiometric calibrations. By comparing HiRISE data to geologic and mineral maps, we find that bright patches are co-located with alteration minerals and major unconformities. Where hydrated silica and phyllosilicates are spatially intermixed, HiRISE color stretches show silica as bright white/blue and phyllosilicates as light brown. Silica detections may represent diagenetically altered zones where the low permeability of nearby phyllosilicates restricted diagenetic fluids. Color variation is also observed at major unconformities, such as between the Murray and the Mound Skirting Unit, as bright strata that appear to gradate downward. Unconformities like this likely represent a change in permeability which may have provided a conduit for diagenetic fluids. The extensive diagenesis seen in Gale implies that subsurface fluids were long-lived and widespread. Understanding diagenesis is crucial for studying astrobiology on Mars because diagenetic fluids affect the formation and preservation of biosignatures.