Evolution of a Lake Margin Recorded in the Sutton Island Member of the Murray Formation, Gale Crater, Mars

This study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar-laminated mudstone with minor intervals of planar sandstone, ripple cross-laminated sandstone, cross-stratified sandstone, and alternating laminated sandstone and mudstone. Meter-thick packages of planar-laminated mudstone in FA1 are interpreted to represent deposition in low-energy ponded environments along the lake margin. Straight- and curve-crested ripple cross-laminated facies are interpreted to represent current-influenced deposition. Cross-stratified sandstone facies consist of dm-thick sets that represent deposition in distal channels. Intercalated mm-scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar-laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine-basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater. This study classifies sedimentary rock characteristics within an interval of sedimentary rock layers comprising the Sutton Island member, which is part of the Murray formation. The main goals of this study are to determine the ancient environments represented by the different sedimentary rock groups (facies) and to understand how ancient environments changed through time. Facies are grouped into two categories (associations) based on their distribution within the stratigraphy: Facies Association 1 (FA1) and Facies Association 2 (FA2). FA1 contains rocks with a range of sedimentary structures and grain sizes and formed via aqueous processes. The environment represented by FA1 is a delta plain adjacent to a lake. Facies Association 2 consists of one fine-grained facies that represents deposition in a lake basin environment. The lowermost interval of stratigraphy is comprised of FA1 (delta plain), which transitions upward into the middle interval of stratigraphy comprised FA2 (lake) and subsequently returns to FA1 in the uppermost stratigraphic interval. Transitions between facies associations represent shifts in the ancient lake shoreline that may have been caused by lake-level change. The delta plain and lake environments represented by FA1 and FA2 are consistent with facies in other members of the Murray formation. The Sutton Island member consists of two distinct facies associations that record delta plain and lacustrine environmentsThe depositional history is indicative of a rapid transgression followed by forced regressionFacies record diverse aqueous processes and expand the range of environments interpreted in the Murray formation