Lack of evidence for paleolakes in the Aeolis Dorsa region, Mars; a mapping investigation

The discovery of impact crater paleolakes, like the discoveries of ancient fluvial valleys, has been instrumental in our developing understanding of the history of water on Mars. Numerous and varied inverted paleo-fluvial deposits have been found within the westernmost lobes (Aeolis and Zephyria Plana) of the Medusae Fossae Formation,-800 km east of Gale Crater (and its inferred paleolake) and just north of the dichotomy boundary. Within the topographic depression between these two plana are located five >10-km-diameter craters that either predate or formed coevally with this fluvial activity, as evidence by stratigraphic relationships. The emplacement of these craters before or during pervasive aqueous activity in the region and their low relative elevation provide the environmental context supportive of the formation of paleolakes in these interplana craters. In this work, we test the hypothesis that these five interplana craters contained lakes by mapping, describing, and interpreting these interior crater deposits. Our primary focus is to identify any potential lacustrine units. Results of this investigation are the identification of sedimentary units with characteristics in support predominately of aeolian and fluvial paleoenvironments, with lacustrine depositional paleoenvironments as an alternative possibility for some units. The lack of conclusive evidence for paleolakes in this environmental context could be due to an actual absence of lakes or alternatively suggests limitations in identifying paleolakes from orbit and the possible presence of more crater paleolakes than have been identified remotely on Mars.