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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 km2 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. Key Points: Twenty‐two candidate deltas occur along the dichotomy boundary in the Gale crater region with delta front elevations spanning approximately 2,400 mFront elevation variations do not correspond to modeled deformation from true polar wander or Tharsis emplacementBased on modern topography, most deltas correspond to enclosed basins, which we infer to be paleo‐lakes, not a northern ocean [ABSTRACT FROM AUTHOR]

With increasing high-resolution coverage of Mars' surface, crater count analysis is being used to estimate the formative ages of small depositional features (<1000 km2) to constrain timing of climate-driven events. We introduce a probabilistic cratering model that quantifies how modeled age estimates vary strongly with crater obliteration rates (β , defined as the combined rate of erosion and infilling), minimum crater diameter counted, and surface area size. Model results show that crater obliteration introduces significant uncertainty on small surfaces, where moderate obliteration rates (β ~ 25 nm a−1) require surface areas of about 10,000 km2 to date 2 to 3 Ga surfaces accurately, and strongly obliterated surfaces (β = 200 nm a−1) require surface areas up to 100,000 km2. In practice, smaller areas can nonetheless be analyzed probabilistically by estimating a range of likely obliteration rate and modeled age combinations and optimizing these values relative to observed crater count data, resulting in a distribution of possible modeled surface ages and associated β. We demonstrate this method using data from the Coprates Chasma landslide (~200 km2) and numerous fan and delta deposits in the Gale crater region. Although the deposits in and around Gale are <1000 km2, a probabilistic analysis enables us to suggest that deltaic deposits in and near Gale have a higher probability of being older (~>3 Ga) than nearby fans (~1–3 Ga). This analysis provides a simple quantitative framework for assigning probable surface age ranges for small features on Mars. • Crater erosion/infilling introduces significant age uncertainty on small surfaces. • We present a probabilistic cratering model that quantifies these uncertainties. • Moderate erosion (>25 nm a−1) requires areas >10,000 km2 for accurate age dating. • We demonstrate this method using data from fan deposits in the Gale crater region. [ABSTRACT FROM AUTHOR]