Ancient oceans in the northern lowlands of Mars: Evidence from impact crater depth/diameter relationships

Abstract

We present depth (d) and diameter (D) data for 2269 Martian impact craters in the diameter range 6–216 km, distributed over ∼11.52 × 106 km2 of terrain that samples several geologic settings and the full range of latitudes and elevations throughout the northern lowlands of Mars. Our data indicate that there are three major crater types that fall into two major populations, those craters that contain Vastitis Borealis formation (VBF) and those that do not. The deepest type 1 craters comprise a Late Hesperian/Early Amazonian‐age population that does not contain VBF. Type 2, type 3, and subdued type 1 craters comprise a population of Hesperian‐age craters partially buried by the VBF. The unique d/D distribution of type 3 craters and photogeologic evidence suggest an erosional style for the VBF that requires sublimation processes, indicating that the VBF contained a substantial amount of ice. Type 3 craters occur throughout the northern lowland plains at elevations below −2400 m. If the VBF is a sedimentary deposit left by a large body of standing water in the northern lowlands of Mars, then the northern lowland plains contained a body of water with a volume of ∼6 × 107 km3 or the equivalent of a 430 m global ocean during the Late Hesperian/Early Amazonian. This also implies that the VBF contains ∼4 × 106 km3 of material, in agreement with the estimated amount of material eroded from the outflow channels surrounding Chryse basin and washed into the northern lowlands.