POSSIBLE UPPER FLOW REGIME SEDIMENTARY STRUCTURES IN THE DILLINGER MEMBER OF THE KIMBERLEY FORMATION, GALE CRATER, MARS: IMPLICATIONS FOR MARTIAN FLUVIAL PROCESSES (Invited Presentation)

Observations of sedimentary rocks on Mars by rovers has shown how terrestrial models for analysing sedimentary deposits can constrain interpretations of sediment transport and depositional systems on another planet. In Gale crater, the Curiosity rover has encountered a rich array of fluvial, deltaic, lacustrine and aeolian clastic sedimentary facies. Here, we report a series of enigmatic sedimentary structures preserved in the “Dillinger” member of the “Kimberley” formation, exposed in the Kimberley region of Aeolis Palus that lies between the rim of Gale crater and Aeolis Mons. The “Dillinger” member comprises a fine- to medium-grained sandstone that is approximately fifty centimetres thick and overlies south-dipping sandstones of the “Square Top” member across a distinct truncation surface. The south-dipping sandstones are interpreted as clinoform geometrical elements deposited as small-scale deltas. The Dillinger member by contrast forms a sub-horizontal stratal unit where it is well exposed at the Kimberley waypoint. The unit was imaged by the Navcam and Mastcam stereo cameras at multiple locations and standoff distances providing detailed data on bedset geometries. Analysis of multiple Mastcam mosaics demonstrates that the Dillinger member is characterised by the presence of ubiquitous undulose lamination forming mounded bed geometries. Typically these undulose bedforms comprise symmetrical convex-up bedsets with laminations traceable across the complete convex-up form. These bedsets are <1 m in wavelength and <10 cm in amplitude. Locally higher-angle cross-bedding dipping to both the south (downstream) and north (upstream) is observed (paleoflow being defined by regional stratigraphic relations). The convex-up bedsets resemble sedimentary structures produced by experimental antidunes in the upper flow regime. Similar bedset geometries have been described from a number of ancient terrestrial fluvial examples and linked to conditions characterised by abrupt discharge variability. In this presentation we consider the possibility that convex-up bedsets in the Dillinger member record deposition from supercritical fluvial flows and evaluate the implications for martian environmental conditions.