Evidence for Middle Amazonian catastrophic flooding and glaciation on Mars

Early geologic investigations of Mars revealed some of the largest channels in the Solar System (outflow channels), which appear to have mostly developed ∼3 byr ago. These channels have been the subject of much scientific inquiry since the 1970s and proposed formative processes included surface erosion by catastrophic floods, glaciers, debris flows and lava flows. Based on the analysis of newly acquired Mars Reconnaissance Orbiter (MRO) Context (CTX, 5.15-5.91 m/pixel) and High Resolution Imaging Science Experiment (HiRISE, 25-50 cm/pixel) image data, we have identified a few locations contained within relatively narrow canyons of the southern circum-Chryse outflow channels that retain well-preserved decameter/hectometer-scale landform assemblages. These terrains include landforms consistent in shape, dimension and overall assemblage to those produced by catastrophic floods, and at one location, to glacial morphologies. Impact crater statistics for four of these surfaces, located within upstream, midstream and downstream outflow channel surfaces, yield an age estimate of ∼600 myr. This suggests that the southern circum-Chryse outflow channels were locally resurfaced by some of the most recent catastrophic floods on the planet, and that these floods coexisted within regional glacier environments as recently as during the Middle Amazonian.