Aeolian scours as putative signatures of wind erosion and sediment transport direction on Mars

Obstacle marks, specifically current crescents (scours) formed by aeolian erosion, have not been previously identified on Mars from orbit. However, recent Mars Reconnaissance Orbiter images of an unnamed intracrater dune field within the Hellespontus region have shown innumerable meter-scale scours around fine and medium grade blocks. The types, relative numbers, and distributions of scour features served to determine, by proxy, the modes of surface wind direction and pathways of sediment transport across the crater floor. The orientations of scours of U-type morphology as well as the facing directions of leeward slopes for crescentic dunes (barchans and barchanoids) and megaripples were examined by statistical methods to determine their reference directions and dispersion of modal classes. We showed that although the dune field has evolved primarily under the influence of winds from the southwest, U-type scours have developed predominantly from a significant northwesterly wind direction. These data suggest that the dune field has evolved under the influence of a bimodal wind regime. Furthermore, such an aeolian system may help to explain the intermediary morphology between crescentic and linear for the central part of the dune field, in which the dunes appear to have undergone longitudinal as well as lateral sediment transport. In the absence of direct measurements of wind directions and strengths, current crescents offer detailed data from which planetary air flow at the surface–air interface can be better interpreted for the many intracrater settings across Mars.