Paleohydrology of Eberswalde Crater, Mars

Abstract

Eberswalde crater, Mars, contains a well-preserved fluvial distributary network in a likely deltaic setting. The meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel-forming discharge (over an individual event flood timescale), runoff production (event and annual timescales), and longevity of deposition (geologic timescale) during the Late Hesperian to Early Amazonian Epochs. The width and meander dimensions of two inverted paleochannels reflect the channel-forming discharge from event floods (~ 200 to 400 m3/s), the deposit surface indicates the level (- 1,400 to - 1,350 m) and surface area (410 to 810 km2) of the likely paleolake, and the topography and mapped extent of tributaries constrain the watershed area (5,000 to 17,000 km2). Based on these results and terrestrial empirical constraints on evaporation and sediment concentration, we evaluated three hypothetical water sources: meltwater liberated by the nearby Holden crater impact (continuous deposition over ~ 101 102 years), intermittent rainfall or snowmelt during finite periods controlled by orbital evolution (deposition over ~ 104 106 years), and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters. Local impact-generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation, respectively, to maintain the paleolake level. The local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations. Multiple primary impact craters in the area postdate Holden ejecta but were later dissected, indicating fluvial erosion long after the Holden impact. Intermittent rainfall of ~ 1 cm/d and seasonal snowmelt are both consistent with our results over a deposition timescale totaling ~ 104 106 years.