Radial thickness variation in impact crater ejecta: implications for lunar basin deposits

Abstract

A review of cratering data and available semi-empirical calculations suggests that the variation of ejecta thickness, t, with increasing range from lunar craters may be approximately modelled by the expression: t=0.14R 0.74(r/R −3.0 where r is range from the center of the crater and R, the crater radius, all in meters. This equation has been used to estimate the thickness of ejecta deposits at each of the Apollo sites contributed from the large multi-ringed frontside lunar basins. Predicted average thickness of Imbrium ejecta at Apollo 15 is 812 m; at Apollo 14, 130 m; at Apollo 17, 102 m; and at Apollo 16, 50 m. Since the sequence of formation of these basins is known, the stratigraphic column resulting from superimposed ejecta blankets can be calculated. Results suggest that pre-Nubium crustal material at upland Apollo sites lies at depths greater than 280 (Apollo 14) to 1940 m (Apollo 17). Predicted stratigraphic sections for the Apollo sites are tabulated.