¹J.D.Tarnas et al. (>10)
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006898]
¹NASA Jet Propulsion Laboratory, California Institute of Technology
Publishe by Arrangement with John Wiley & Sons

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine-bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake-inhabiting lifeforms. Here we show that carbonate-bearing rocks within and outside of Jezero crater have the same range of visible-to-near-infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate-bearing rock cross-sections in Jezero crater are ∼75-90 meters thicker than typical ROB unit cross-sections in the Nili Fossae region, but have similar thicknesses as ROB unit exposures in Libya Montes. These similarities in carbonate properties inside and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg- and more Fe-rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non-deltaic carbonates within and outside of Jezero crater.

¹Naoma McCall,^1,2Sean P.S.Gulick,³Brendon Hall,^4.5Auriol S.P.Rae,⁴Michael H.Poelchau,⁶Ulrich Riller,⁷Johanna Lofi,⁸Joanna V.Morgan
Earth and Planetary Science Letters 576, 117236 Link to Article [https://doi.org/10.1016/j.epsl.2021.117236]
¹University of Texas at Austin, Jackson School of Geosciences, Institute for Geophysics & Department of Geological Sciences, J.J. Pickle Research Campus, Austin, TX 78758, USA
²Center for Planetary Systems Habitability, University of Texas at Austin, Austin, TX, USA
³Enthought, Inc., Austin, TX, USA
⁴Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs Universität Freiburg, Albertstrasse 23b, Freiburg 79110, Germany
⁵Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
⁶Institut für Geologie, Universität Hamburg, Bundesstrasse 55, Hamburg, 20146, Germany
⁷Géosciences Montpellier, Université de Montpellier, CNRS, France
⁸Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
Copyright Elsevier

Hypervelocity impact cratering is an important geologic process but the rarity of large terrestrial impact craters on Earth and the limited technical options to study cratering processes in the laboratory hinders our understanding of large-scale impact processes. Drill core recovered from the peak ring of the Chicxulub impact crater during International Ocean Discovery Program (IODP)/International Continental scientific Drilling Program (ICDP) Expedition 364 provides an opportunity to examine target rock deformation and thus, to assess cratering models in this regard. Using oriented computer tomography (CT) scans and line scan images of the core, we present the orientations of mm-to-cm-scale planar cataclasite and ultracataclasite zones in the deformed granitoid target rock of the peak ring. In the upper 470 m of the target rock, the cataclasite zones dip towards the crater center, whereas the dip directions for the ultracataclasite zones are approximately tangential to the peak ring. These two orientations are consistent with deformation expected from hydrocode-modeled principal stress directions for the outward movement of rocks as the transient crater develops, and the inward movement of rocks associated with collapse of the transient crater. Near the base of the core is a 96 m-thick interval of highly-deformed target rock with impact melt rock and rock fragments not observed elsewhere in the core; this interval has previously been interpreted as an imbricate thrust zone within the peak ring. The cataclasite zones below this thrust zone have different orientations than those in the 470 m-thick block above. This observation implies a differential rotation from the overlying block during the final stages of peak-ring formation. Our results support an acoustic fluidization process, wherein blocks that vibrate or slide relative to each other allow the target rock to flow during transient crater collapse, and that the size of coherent rock blocks increases over the course of crater modification as the target rock regains its cohesive strength and acoustic fluidization decreases.