Paleoenvironments and petrologic history of the Hartmann’s Valley, Karasburg, and Sutton Island members of the Murray formation, Gale crater, Mars

Today, the surface of Mars is predominantly shaped by aeolian processes, yet stratigraphic and compositional evidence suggests that rivers, deltas, and lakes occurred in the geologic past. Orbital and rover analyses of stratigraphy provides evidence that Gale crater, the site of the Mars Science Laboratory Curiosity rover mission, once contained paleolake and lake-margin environment(s) recorded in the 320 m thick Murray formation. This research utilizes combined sedimentologic, stratigraphic, and compositional analyses to investigate three stratigraphic members of the Murray formation. The primary goal of these chapters is to determine ancient environments and sedimentary processes recorded in stratigraphy and to assess the evolution of aqueous systems compared to the overall Murray formation.

Chapter 1 presents facies and geochemical analyses of the Hartmann’s Valley and Karasburg members, which were initially distinguished by intervals of meter-scale cross-stratified sandstone. Three facies are described: cross-stratified sandstone, planar-laminated sandstone, and planar-laminated mudstone. Sandstone facies represent wet aeolian dune and interdune environments along a lake margin, and mudstone facies represent deposition in a long-lived lake basin. Compositional trends record moderate chemical weathering and hydrodynamic sorting of sediment in transport. The stratigraphic distribution of facies is indicative of an interval of lake expansion.

Chapter 2 details facies analysis of the overlying Sutton Island member, which consists of two facies associations: (a) Facies Association 1 (FA1) and (b) Facies Association 2 (FA2). Facies Association 1 represents the lowermost and uppermost intervals of stratigraphy, and consists of distal delta plain facies. Facies Association 2 represents the middle interval of stratigraphy and consists of planar-laminated mudstone, interpreted to represent deposition in a lacustrine environment characterized by sufficient standing water to allow for accommodation of strata. The first transition from FA1 to FA2 is interpreted to represent a rapid transgression, followed by a forced regression from FA2 back to FA1.

Chapter 3 focuses on the compositional record of source rock, weathering, transport, and diagenesis within the Sutton Island member stratigraphy through contextualization with Facies Associations interpreted in Chapter 2. Facies represent a basaltic source primarily from the crater rim. Moderate weathering is indicated by weathering indices and geochemical trends. Immobile oxides provide some evidence for hydrodynamic sorting, and geochemical overlap between facies and grain sizes may be indicative of an aphyric source composition or a restricted grain-size range between FA1 and FA2. Overall, whole-rock geochemical signatures highlight the longevity of aqueous processes from sediment formation through lithification.