Stratigraphic Evidence of Backwater Morphodynamics and Lowland River Deltas in the Northern Hemisphere of Mars

This study explores how specific hydraulic and sedimentation patterns, referred to as backwater morphodynamics, occur in river systems near the coast, and whether these patterns also exist on Mars. On Earth, we observe, in river systems like the Mississippi, the width of the channel belt (the region where a river distributes sand) decreases to roughly 2–6 times the channel width within what we call the backwater/belt-width window. We measured the widths of nine river delta channel belts from the surface of Mars and found their backwater/belt-width window upstream from an ancient shoreline. The locations of these windows provide an estimate for the length scale of the backwater zone for each delta, which notably coincides with the location of avulsion nodes. The confirmation of these relationships in martian stratigraphy demonstrates that backwater morphodynamics is a planetary phenomenon and should be present on all planets with river systems, whether ancient or active (e.g., Earth, Mars, and Titan). Backwater morphodynamic relationships can be used as a tool to discover other important characteristics about river systems, like paleogeography, slope, and grainsize. Importantly, our results provide new evidence consistent with an ancient ocean in the northern hemisphere of Mars.