(LAC-25) Geologic map of the Cassini quadrangle of the Moon

The Cassini quadrangle is in the north-central part of the nearside lunar disk and includes most of the northeast quadrant of Mare Imbrium. Lunar geologic units in the area have been distinguished according to topographic expression, albedo, and infrared stratigraphic relations, and the distribution of each unit is portrayed on the accompanying map. the nature and disposition of geologic units in the area was largely controlled by the formation of the Imbrium basin and its subsequent filling by mare material. Four principal classes of geologic units can be distinguished: (1) material of three rugged arcuate mountain ranges circumferential to the Imbrium basin; (2) terra materials superposed on these ranges; (3) mare materials; and (4) crater materials. An additional unit, bright slope material, indicates fragmental debris from, and fresh exposures of, these units. The relative ages of the units are determined by a variety of criteria, including superposition and transection relations, density of superposed craters and, in the case of craters, apparent topographic freshness. Age designations are assigned according to the lunar stratigraphic scheme devised as a result of studies of the geologically similar Copernicus region south of the quadrangle (Shoemaker, 1962; Shoemaker and Hackman, 1962; later revisions are reported by McCauley, 1967 and Wilhelms, in press).