Degradation of Small Simple and Large Complex Lunar Craters: Not a Simple Scale Dependence

The crater record of a planetary surface unit is often analyzed by its cumulative size-frequency distribution (CSFD). Measuring CSFDs involves traditional approaches, such as traditional crater counting (TCC) and buffered crater counting (BCC), as well as geometric corrections, such as nonsparseness correction (NSC) and buffered nonsparseness correction (BNSC). NSC and BNSC consider the effects of geometric crater obliteration on the CSFD. On the Moon, crater obliteration leads to two distinct states in which obtained CSFDs do not match the production CSFD-crater equilibrium and nonsparseness. Crater equilibrium occurs when each new impact erases a preexisting crater of the same size. It is clearly observed on lunar terrains dominated by small simple craters with steep-sloped production CSFDs, such as Imbrian to Eratosthenian-era mare units. Nonsparseness, on the other hand, is caused by the geometric overlap of preexisting craters by a new impact, which is also known as "cookie cutting." Cookie cutting is most clearly observed on lunar terrains dominated by large craters with shallow-sloped production CSFDs, such as the pre-Nectarian lunar highlands. We use the Cratered Terrain Evolution Model (CTEM) to simulate the evolution of a pre-Nectarian surface unit. The model was previously used to simulate the diffusion-induced equilibrium for small craters of the lunar maria. We find that relative to their size, large craters contribute less to the diffusion of the surrounding landscape than small craters. Thus, a simple scale dependence cannot account for the per-crater contribution to degradation by small simple and large complex craters.