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

Abstract Backwater morphodynamics describe feedbacks between hydraulics and sedimentation in fluvio‐deltaic systems in the coastal backwater zone. On Earth, normalized channel belt width decreases approaching the coastline and drops sharply at the start of the backwater zone. This systematic decrease allows a backwater/belt‐width window to be defined, one backwater length upstream from the coast with normalized widths from 2 to 6. We use the backwater/belt‐width window to interpret backwater morphodynamics and estimate backwater length on Mars using narrowing channel belts at Aeolis Dorsa. We measure nine belts from martian delta deposits and compare normalized width to distance upstream from an ancient shoreline. Estimates range from ∼5 to 17 km, coinciding with lengths derived from avulsions. Observing these relationships on Mars demonstrates the universality of backwater morphodynamics, providing new methods for understanding martian hydrologic history. Notably, our results indicate Aeolis Dorsa deltas resembled lowland river deltas on Earth, consistent with a northern hemispheric ocean.