Caloris Basin
Rock units associated with the Caloris Basin are particularly important for the stratigraphy of Mercury. It has been demonstrated that the history of the Moon was punctuated by a series of major impacts that have emplaced ejecta over widespread areas; the rock units associated with these impact basins were used to divide the lunar stratigraphic column into a series of well-defined time units (Shoemaker and Hackman, 1962; McCauley, 1967; Wilhelms, 1972). These relations are particularly clear for the Imbrium Basin (Wilhelms and McCauley, 1971) and Orientale Basin (Scott and others, 1977).