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Widespread Amazonian-aged fluvial channels have been mapped proximal to Lyot crater, a similar to 225km diameter impact basin in the northern lowlands of Mars. Comparable in area to some Noachian/Hesperian fluvial systems, their morphology differs, being dominated by broad, shallow braided channels. Using new developments in the study of cratering, water inventory, and climate history, we assess eight different models for their origin. Dewatering of excavated ice-rich Lyot ejecta and contact melting from hot Lyot ejecta superposed on surface ice deposits are the most plausible channel origins. The existence of this extensive Amazonian fluvial system is attributed to: (1) the large size of Lyot, and its consequent hot ejecta, and (2) the presence of surface ice at the time of impact, attributed to obliquity changes redistributing polar ice to the mid-latitudes, a relatively common occurrence in Martian geologic history.

Plain Language Summary A vast network of relatively young broad and shallow fluvial channels were previously mapped near Lyot crater, a similar to 225km diameter impact basin located in one of the lowest regions of Mars. These channels are highly unusual based on their young age and dispersed scour morphology. We use new developments in the study of cratering, water inventory, and climate history to assess different models for the origin of these channels. We find that the fluvial channels likely formed through runoff of water derived from dewatering of melted pore ice from within the ejecta and/or meltwater from contact melting of hot Lyot ejecta superposed on a regional surface ice sheet. The existence of this extensive young fluvial system is attributed to: (1) the large size of Lyot, and its consequent hot ejecta, and (2) the presence of surface ice at the time of impact, attributed to obliquity changes redistributing polar ice to the mid-latitudes, a relatively common occurrence in Martian geologic history.