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Deltaic deposits mapped along the Martian crustal dichotomy boundary scarp have been suggested to delineate an ancient ocean in the northern lowlands of Mars. Using recently acquired orbital data, we have expanded the dichotomy delta inventory and performed an updated analysis of delta front elevations, a proxy for paleo-water levels. Our analysis focused near Gale crater, home of the Curiosity rover. We found that delta front elevations vary by approximately 2,400 m, but these elevation variations do not correspond to modeled deformation from true polar wander or Tharsis. Locally, delta front elevations vary by <= 60 m, and using present-day topography, they correspond to distinct enclosed basins. We infer that these deltas formed in paleo-lakes up to approximately 13,000 km(2) and approximately 0.4 km deep, perhaps coeval with paleo-lakes in Gale. Our results suggest that a northern ocean is not needed to explain the deltaic deposits in the Gale crater region.

Plain Language Summary The climate of early Mars is debated. Climate modeling suggests that it was always cold and dry, while geologic evidence suggests that it was much wetter in the past, possibly supporting a northern ocean. Evidence in support of a northern ocean includes deltaic deposits along the margins of the northern lowlands. However, the elevations of these deltas vary greatly, calling into question whether they were all deposited into the same body of water. To test this hypothesis, we used high-resolution satellite imagery and topography to investigate a large number of lowland deltas in the vicinity of Gale crater, home to the Curiosity rover. We have found that the variability in delta elevations is not due to postformational deformation, rather most deltas in this region formed into lakes, similar in size to the Great Lakes on Earth. These findings show that a northern Martian ocean is not needed to explain the deltas in the vicinity of Gale crater.