Redefinition of the crater-density and absolute-age boundaries for the chronostratigraphic system of Mars

For the boundaries of each chronostratigraphic epoch on Mars, we present systematically derived crater-size frequencies based on crater counts of geologic referent surfaces and three proposed “standard” crater size–frequency production distributions as defined by (a) a simple −2 power law, (b) Neukum and Ivanov, (c) Hartmann. In turn, these crater count values are converted to model-absolute ages based on the inferred cratering rate histories. We present a new boundary definition for the Late Hesperian–Early Amazonian transition. Our fitting of crater size–frequency distributions to the chronostratigraphic record of Mars permits the assignment of cumulative counts of craters down to 100 m, 1 km, 2 km, 5 km, and 16 km diameters to martian epochs. Due to differences in the “standard” crater size–frequency production distributions, a generalized crater-density-based definition to the chronostratigraphic system cannot be provided. For the diameter range used for the boundary definitions, the resulting model absolute age fits vary within 1.5% for a given set of production function and chronology model ages. Crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10%.