Depositional and Diagenetic Processes of Martian Lacustrine Sediments as Revealed at Pahrump Hills by the Mars Hand Lens Imager, Gale Crater, Mars

The Murray formation represents fine-grained sedimentary deposition in lacustrine environments within Gale crater, Mars. Both the overall thickness of the Murray formation and its broad uniformity in sedimentary character suggest the potential for a long-lived, groundwater-supported lake system. Rock textures were imaged by the Mars Hand Lens Imager camera at the Pahrump Hills location, which represents the lowermost Murray formation. We analyze data from Pahrump Hills to refine earlier estimates of grain size and grain size distribution, as well as to make detailed observations of diagenetic features and modification of primary sedimentological features. These observations and resulting interpretations provide a detailed look at the dynamic behavior of lake systems on Mars. The lower portions of this exposure are characterized by planar laminated, fine-grained material; the predominant grain size in this region is smaller than that of very fine sand. Diagenetic mineral precipitation is also prominent in these lower layers, evidenced by likely in situ precipitation of lenticular crystals, preferential cementation of laminae in several layers, precipitation of late-diagenetic crystal clusters, and secondary modification of previously deposited crystals. The upper portions of this locality are coarser-grained, varicolored, and contain cross-stratified features. The variation of these features over a relatively thin stratigraphic interval indicates rapid fluctuation in the hydrodynamic behavior of Gale crater lake, similar to that observed in the shallow-water regions of terrestrial closed basin lakes.