Grjotá Valles and implications for flood sediment deposition on Mars

Grjotá Valles is one of Mars' four Amazonian-aged, fissure-headed, catastrophic flood channels. It originates at the northwestern-most Cerberus Fossa and stretches several hundred kilometers eastward and southward. Moats around in-channel knobs and various small-scale mounds, similar to mounds seen in Athabasca Valles, are both attributed to flood-related processes. The floodwater sinks are ambiguous, and the lack of recognizable flood deposits is attributed to two causes, The first cause is the channel's high width-to-depth ratio, which may have facilitated floodwater recession during flooding. The second cause is the tendency of floodwater under lower gravity to move a higher percentage of material as washload. As flood deposits are comprised of bedload and suspended load, this tendency would result in fewer depositional bedforms. Our analysis of Grjotá Valles supports the idea that formation of terrestrial-style flood deposits is energetically unlikely on Mars and that their presence indicates special paleohydraulic conditions.