Browsing by Author "Grotzinger, John P."

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    Burial and Exhumation of Sedimentary Rocks Revealed by the Base Stimson Erosional Unconformity, Gale Crater, Mars
    (Wiley, 2022) Watkins, Jessica A.; Grotzinger, John P.; Stein, Nathan T.; Banham, Steven G.; Gupta, Sanjeev; Rubin, David M.; Morgan, Kathryn Stack; Edgett, Kenneth S.; Frydenvang, Jens; Siebach, Kirsten L.; Lamb, Michael P.; Sumner, Dawn Y.; Lewis, Kevin W.
    Sedimentary rocks record the ancient climate of Mars through changes between subaqueous and eolian depositional environments, recognized by their stratal geometries and suites of sedimentary structures. Orbiter- and rover-image-based geologic mapping show a dynamic evolution of the 5-km-thick sedimentary sequence exposed along the flanks of Aeolis Mons (informally, Mt. Sharp) in Gale crater, Mars, by deposition of subaqueous strata followed by exhumation via eolian erosion and then deposition of overlying, onlapping strata of inferred eolian origin. This interpretation suggests that a significant unconformity should occur at the base of the onlapping strata, thus predicting lateral variations in elevation along the contact between the underlying Mt. Sharp group and overlying Stimson formation. Curiosity rover and high-resolution orbital image data quantify paleotopographic variability associated with the contact; ∼140 m of net elevation change and a slope closely aligned with the modern topography is expressed along the regional contact. These results support the interpretation of an erosional unconformity between these strata and that it was likely formed as a result of eolian erosion within the crater, indicative of a transition from wet to dry climate and providing insight into the stratigraphic context, geologic history, and habitability within Gale crater.
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    Extraformational sediment recycling on Mars
    (The Geological Society of America, 2020) Edgett, Kenneth S.; Banham, Steven G.; Bennett, Kristen A.; Edgar, Lauren A.; Edwards, Christopher S.; Fairén, Alberto G.; Fedo, Christopher M.; Fey, Deirdra M.; Garvin, James B.; Grotzinger, John P.; Gupta, Sanjeev; Henderson, Marie J.; House, Christopher H.; Mangold, Nicolas; McLennan, Scott M.; Newsom, Horton E.; Rowland, Scott K.; Siebach, Kirsten L.; Thompson, Lucy; VanBommel, Scott J.; Wiens, Roger C.; Williams, Rebecca M.E.; Yingst, R. Aileen
    Extraformational sediment recycling (old sedimentary rock to new sedimentary rock) is a fundamental aspect of Earth’s geological record; tectonism exposes sedimentary rock, whereupon it is weathered and eroded to form new sediment that later becomes lithified. On Mars, tectonism has been minor, but two decades of orbiter instrument–based studies show that some sedimentary rocks previously buried to depths of kilometers have been exposed, by erosion, at the surface. Four locations in Gale crater, explored using the National Aeronautics and Space Administration’s Curiosity rover, exhibit sedimentary lithoclasts in sedimentary rock: At Marias Pass, they are mudstone fragments in sandstone derived from strata below an erosional unconformity; at Bimbe, they are pebble-sized sandstone and, possibly, laminated, intraclast-bearing, chemical (calcium sulfate) sediment fragments in conglomerates; at Cooperstown, they are pebble-sized fragments of sandstone within coarse sandstone; at Dingo Gap, they are cobble-sized, stratified sandstone fragments in conglomerate derived from an immediately underlying sandstone. Mars orbiter images show lithified sediment fans at the termini of canyons that incise sedimentary rock in Gale crater; these, too, consist of recycled, extraformational sediment. The recycled sediments in Gale crater are compositionally immature, indicating the dominance of physical weathering processes during the second known cycle. The observations at Marias Pass indicate that sediment eroded and removed from craters such as Gale crater during the Martian Hesperian Period could have been recycled to form new rock elsewhere. Our results permit prediction that lithified deltaic sediments at the Perseverance (landing in 2021) and Rosalind Franklin (landing in 2023) rover field sites could contain extraformational recycled sediment.