Diagenetic History and Biosignature Preservation Potential of Fine‐Grained Rocks at Hogwallow Flats, Jezero Crater, Mars

The Mars 2020 Perseverance rover discovered fine‐grained clastic sedimentary rocks in the “Hogwallow Flats” member of the “Shenandoah” formation at Jezero crater, Mars. The Hogwallow Flats member shows evidence of multiple phases of diagenesis including Fe/Mg‐sulfate‐rich (20–30 wt. %) outcrop transitioning downward into red‐purple‐gray mottled outcrop, Fe/Mg clay minerals and oxides, putative concretions, occasional Ca sulfate‐filled fractures, and variable redox state over small (cm) spatial scales. This work uses Mastcam‐Z and SuperCam instrument data to characterize and interpret the sedimentary facies, mineralogy and diagenetic features of the Hogwallow Flats member. The lateral continuity of bedrock similar in tone and morphology to Hogwallow Flats that occurs over several km within the western Jezero sedimentary fan suggests widespread deposition in a lacustrine or alluvial floodplain setting. Following deposition, sediments interacted with multiple fluids of variable redox state and salinity under habitable conditions. Three drilled sample cores were collected from this interval of the Shenandoah formation as part of the Mars Sample Return campaign. These samples have very high potential to preserve organic compounds and biosignatures. Drill cores may partially include dark‐toned mottled outcrop that lies directly below light‐toned, sulfate‐cemented outcrop. This facies may represent some of the least oxidized material observed at this interval of the Shenandoah formation. This work reconstructs the diagenetic history of the Hogwallow Flats member and discusses implications for biosignature preservation in rock samples for possible return to Earth. Plain Language Summary The Mars 2020 Perseverance rover discovered sedimentary rocks in Jezero crater during the second year of its mission. Some of these rocks were informally named the “Hogwallow Flats” member of the “Shenandoah” formation. These rocks contain abundant clay minerals and sulfates, indicating ancient interactions with liquid water. They may preserve organic matter and signs of life that could tell us whether life was ever present in Jezero crater billions of years ago. The sediments here appear to have undergone physical and chemical changes after deposition—called diagenesis—when interacting with liquid water. These changes, which may have occurred in a lake or a shallow river plain and later when the sediments were shallowly buried, are often associated with favorable conditions for pr