Sedimentological and Geochemical Perspectives on a Marginal Lake Environment Recorded in the Hartmann's Valley and Karasburg Members of the Murray Formation, Gale Crater, Mars. Issue 8 (17th August 2022) - Gwizd, S.
Abstract: This study utilizes instruments from the Curiosity rover payload to develop an integrated paleoenvironmental and compositional reconstruction for the 65‐m thick interval of stratigraphy comprising the Hartmann's Valley and Karasburg members of the Murray formation, Gale crater, Mars. The stratigraphy consists of cross‐stratified sandstone (Facies 1), planar‐laminated sandstone (Facies 2), and planar‐laminated mudstone (Facies 3). Facies 1 is composed of sandstone showing truncated sets of concave‐curvilinear laminae stacked into cosets. Sets are estimated to be meter‐to sub‐meter‐scale, consistent with low‐height dunes. Thin stratigraphic intervals of Facies 1 and stacking patterns with Facies 2 and 3 support a wet aeolian dune interpretation. Meter‐thick packages of planar‐laminated sandstone (Facies 2) are interpreted to represent interfingering dune‐interdune strata. Facies 3 consists of meter‐thick packages of planar‐laminated mudstone interpreted to represent lacustrine deposition with persistent standing water. Integration of geochemistry with each facies reveals some compositional control based on the depositional process. Models for source rock composition from Alpha Particle X‐Ray Spectrometer measurements show that facies derived from a basaltic source. Alteration indices and geochemical trends provide evidence that moderate chemical weathering occurred before compositional changes due to diagenesis. Differences in wt% FeO(T) and TiO2 between facies are minimal, though trends point to sediment sorting in transport. Comparisons to terrestrial basaltic sedimentary systems indicate that the Hartmann's Valley and Karasburg facies reflect deposition in an environment where diverse subaqueous and subaerial facies persisted adjacent to a long‐lived body of water. Plain Language Summary: This study utilizes instruments from the Curiosity rover payload to study the facies and geochemistry of an interval of sedimentary rocks exposed at Gale crater on Mars. The Hartmann's Valley and Karasburg members, the focus of this study, contain sedimentary facies that represent ancient lake and lake‐margin environments. Lake deposits are consistent with deposition in standing water. Lake‐margin deposits are consistent with wet subaerial dune and interdune formation. Models indicate that sediments for all facies were derived from a similar source composition. Geochemical trends indicate that sediment composition changed via chemical weathering. Slight compositional trends that correlate with relative grain size signatures suggest that sediment may have been sorted in transport. Facies and geochemistry collectively indicate that the depositional environments of the Hartmann's Valley and Karasburg members persisted in a climate capable of sustaining standing water within lakes and along lake margins. Key Points: Subaerial and subaqueous facies were identified within stratigraphy of the Hartmann's Valley and Karasburg members of the Murray formation Sedimentologic, stratigraphic, and geochemical evidence suggests that facies formed in a landscape capable of sustaining water These members extend the range of facies and environments identified within the Murray formation