Formation of lunar basin rings

The outer rings of impact basins are interpreted as the bounding rings of the excavated basin cavities analogous to Copernicus-type crater rim crests. It is suggested that the inner rings are strata from depth uplifted during excavation of the transient cavity. Spacing relations and morphology appear to indicate a transition from central peaks to rings but not from terraces to rings. Evidence related to terrestrial craters with rings or peaks produced by meteorite impacts suggests that one or more crater rims may form inside the main, outer crater rim, resulting in nested craters. There is some evidence that peaks grade into inner rings as material is ejected from their cores in progressively larger impacts. Multiply layered materials may produce multiple rings by differential excavation of the layers.