Valley formation in Margaritifer Sinus, Mars, by precipitation-recharged ground-water sapping

Drainage morphometry and geologic mapping place new constraints on valley o rigin in Margaritifer Sinus, Mars. Preserved valleys are constant width, ty pically head near divides, possess fourth-order trunk segments, and were fo rmed from late Noachian into earliest Hesperian time. Relative to terrestri al systems, the Martian valleys have low densities (<0.1 km/km(2)), relief ratios (0.001-0.13), and ruggedness numbers (0.005-0.086), and the sediment volume in associated sinks exceeds the volume excavated by upstream segmen ts. Valley characteristics are consistent with formation by precipitation-r echarged ground-water sapping within a layered, permeable substrate.