GSA Connects 2021 in Portland, Oregon

Paper No. 14-7
Presentation Time: 9:35 AM


KAH, Linda, University of Tennessee, Knoxville, TN 37996, GUPTA, Sanjeev, Imperial College London, London, SW7 2AZ, United Kingdom, SIMON, Justin I., NASA Johnson Space Center, Houston, TX 77058 and BENISON, Kathleen, West Virginia University, Morgantown, WV 26506

Jezero crater is characterized by a prominent fluvial-deltaic deposit along the western margin of the crater, and a morphologically diverse set of olivine- and pyroxene-bearing deposits exposed across the crater floor. Most prominent of these crater floor deposits is a dark-toned, crater-retaining unit with lobate margins. This unit has long been hypothesized to be a “volcanic floor” deposit because its chemical composition and its regional morphology—both observed from orbit—appears consistent with emplacement as a basaltic flow. Prior to landing of the Perseverance rover, more detailed morphological investigation of this dark-toned crater floor from orbital images suggested a more complex origin that likely reflects emplacement and superposition of several morphologically discrete rock units, alteration by impact cratering, burial and subsequent exhumation, and modification by wind.

Here we use high-resolution images taken by the Mastcam-Z, Supercam RMI, and WATSON imaging systems on board the Perseverance rover to provide an overview of the dark-toned crater floor unit in the landing site region. We describe the macro-scale morphological features and distribution of primary rock morphotypes, and we explore the range of meso-scale and micro-scale textural features observed in these rocks. Despite the challenges of interpreting lithology of materials that have undergone substantial surface modification (e.g., sculpting and polishing) by wind, and that often have dust coverage that obscures surface textures, we provide evidence that rocks of the dark-toned crater floor are composed primarily of granular materials that vary in both grain size and in the thickness of discrete beds. We suggest that emplacement occurred primarily via hydrodynamically driven sedimentary deposition—although tephra deposition into subaqueous or subaerial environments cannot be ruled out for certain morphotypes—and explore the extent to which differences in surficial modification can obscure depositional signals.