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

Abstract 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.