From Lake to River: Documenting an Environmental Transition across the Jura/Knockfarril Hill Members Boundary in the Glen Torridon Region of Gale crater (Mars)

1,2G.Caravaca et al. (>10)
Journal of Geophysical Research (Planets) Open Access Link to Article [https://doi.org/10.1029/2021JE007093]
1UMR 5277 CNRS, UPS, CNES Institut de Recherche en Astrophysique et Planétologie, Université Paul Sabatier Toulouse III, Toulouse, France
2UMR 6112 CNRS Laboratoire de Planétologie et Géosciences, Nantes Université, Université d’Angers, Nantes, France
Published by arrangement with John Wiley & Sons

Between January 2019 and January 2021, the Mars Science Laboratory team explored the Glen Torridon region in Gale crater (Mars), known for its orbital detection of clay minerals. Mastcam, MAHLI and ChemCam data are used in an integrated sedimentological and geochemical study to characterize the Jura member of the upper Murray formation and the Knockfarril Hill member of the overlying Carolyn Shoemaker formation in northern Glen Torridon. The studied strata show a progressive transition represented by interfingering beds of fine-grained, recessive mudstones of the Jura member and coarser-grained, cross-stratified sandstones attributed to the Knockfarril Hill member. Whereas the former are interpreted as lacustrine deposits, the latter are interpreted as predominantly fluvial deposits. The geochemical composition seen by the ChemCam instrument show K2O-rich mudstones (∼1-2 wt.%) vs MgO-rich sandstones (>6 wt.%), relative to the average composition of the underlying Murray formation. We document consistent sedimentary and geochemical datasets showing that low-energy mudstones of the Jura member are associated with the K-rich endmember, and that high-energy cross-stratified sandstones of the Knockfarril Hill member are associated with the Mg-rich endmember, regardless of stratigraphic position. The Jura to Knockfarril Hill transition therefore marks a significant paleoenvironmental change, where a long-lived and comparatively quiescent lacustrine setting progressively changes into a more energetic fluvial setting, as a consequence of shoreline regression due to either increased sediment supply or lake-level drop.

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