INSIGHTS INTO JEZERO CRATER GEOLOGY FROM ROCK-REGOLITH INTERFACES

The Mars 2020 rover has begun exploring the floor of Jezero crater, a putative ancient lake floor hosting exposures of bedrock, loose rocks of various sizes, and regolith along the rover traverse. Here we describe the potential of rock-regolith interfaces to preserve unique records of geological processes and powerfully supplement rock-specific observations on Mars. Linking observations of local rock texture with associated regolith reveals important lithologic information due to the relations between differential weathering behavior and mineralogy, grain size, and cement chemistry.

Material weathered directly from local bedrock exposures is potentially distinct from other regolith components transported by wind from distant sources. This work explores the possibility that some regolith is derived locally from immediately-adjacent rock exposures and reports insights gained from coordinated imaging and spectroscopic observations of rock-regolith interfaces that decoupled observations of rock or regolith alone may have overlooked. Initial measurements of elemental composition from the remote laser (1064 nm) induced breakdown spectra taken with the SuperCam instrument indicate rock-regolith transitions highlight endmembers in the chemical composition and grain size data reported. Gradients of chemical composition as well as the development of dust coatings on dark rocks that are of potential mafic composition with reflective Ti features, are apparent.

Remote observations across rock-regolith transitions also suggest relative differences in hardness, the extent of chemical weathering, and the presence of potential lithifying areas. Grain size may impact the elemental composition heterogeneity observed in regolith adjacent to rock, with greater heterogeneity found in the fine- to medium-grained fractions. Preliminary near-infrared relative reflectance spectra from SuperCam suggests that many of the rock surfaces exhibit absorptions in the 1.9 μm region and are consistent with hydration, possibly from alteration processes, whereas regolith exhibits variable but overall weaker absorptions. Overall, a rock-regolith perspective improves geological interpretations gained and furthers the study of potential dust regolith hazards in preparation for human exploration.