Stratigraphy of Carbonate-Bearing Rocks at the Margin of Jezero Crater, Mars: Evidence for Shoreline Processes?

Martian carbonate‐bearing rocks are compelling targets for exploration because they preserve detailed records of past aqueous processes, climate, and habitability. The Margin unit in Jezero crater is a distinct olivine‐ and carbonate‐bearing unit stratigraphically underlying the western fan, lining the inner margin of the western crater rim and has a contested origin. Perseverance spent ∼350 sols investigating the unit as part of its fourth mission campaign, aiming to constrain its origin, alteration history and biosignature preservation potential. This study reports on the lithofacies and stratigraphy of the unit by analyzing Mastcam‐Z mosaics and derived 3D outcrop models, supplemented by long‐distance SuperCam observations and detailed textural analyses from SHERLOC WATSON and ACI images. We find that the Margin unit comprises two distinct sub‐units. The Eastern Margin Unit (EMU) comprises well‐stratified, low‐angle basinward‐, rimward‐ and sub‐horizontally inclined medium‐grained sandstones which preserve angular to rounded grains, occasional cross‐stratification, convex‐up bedding, and erosion surfaces. The Western Margin Unit (WMU) comprises distinctly structureless to decimeter‐scale parallel‐layered rocks which drape the crater rim and are inclined into the crater. The origin of the WMU is uncertain but may be most consistent with a variably carbonated olivine cumulate. The favored depositional model for the EMU is a lacustrine shore zone environment where sediments derived from the adjacent WMU have been locally reworked by wave action along a paleoshoreline at around –2,400 m elevation. These observations suggest that the Margin unit preserves diverse subsurface and surface aqueous environments and further extends the habitability window at Jezero crater.

The authors wish to thank all members of the Mars 2020 science and engineering teams for their hard work in tactical and strategic science operations and for making this paper possible. We also wish to pay particular thanks to the Mars 2020 project management and campaign science leads for their efforts in making the mission a success, as well as the Mastcam-Z, SuperCam and SHERLOC operations teams for their hard work and investment in the mission and in acquiring the data products used here. We would also like to thank Dr Michelle Tebolt and one anonymous reviewer for their thorough feedback and suggestions during the review process. A. J. Jones was funded by the Imperial College London President's PhD Scholarship. UK Space Agency Grants ST/Y000153/1 and ST/X002373/1 funded S. Gupta and R. Barnes. G. Paar was supported by FFG ASAP Mars 4-D Grant 911911. B. Horgan, B. Garczynski, A. Klidaras and J. Bell III were funded by NASA's Mars 2020 Project via a subcontract from the California Institute of Technology/Jet Propulsion Laboratory to Arizona State University (Subcontract 1511125). Jet Propulsion Laboratory subcontract 16769020 funded K. H. Williford. K. Stack, J. Maki, N. R. Williams, F. J. Calef, L. R. W. Ives and S. Gwizd carried out their research contributions at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). J. I. Simon was funded by the Return Sample Science Participating Scientist Program supported by the NASA Mars Exploration Program. E. Ravanis was funded by NASA's Mars 2020 project via ASU subcontract 15–711. L. C. Kah was funded by the SHERLOC-WATSON instrument team. O. Beyssac and G. Caravaca were supported by the French Space Agency CNES.