Ballistic Sedimentation of Impact Crater Ejecta: Implications for the Provenance of Lunar Samples and the Resurfacing Effect of Ejecta on the Lunar Surface

A clear understanding of ballistic sedimentation is critical for interpreting the evolution of the lunar surface and the provenance of lunar samples. Quantitative models have been established to estimate the characteristics of ejecta deposits, such as the abundance of distantly sourced ejecta compared to the amount of excavated local materials. Here, we revise a previously established ballistic sedimentation model by considering the shielding effect of ejecta deposits on the emplacement process of later-arriving ejecta. Our model shows that, due to the shielding effect, the ratio of excavated local materials to ejecta in continuous ejecta deposits increases significantly with increasing distance from the center of their parent crater. Model-derived results imply that basin formation resurfaces regions within continuous ejecta deposits and proximal light plains but only partially resurfaces distal areas; thus, the partial resurfacing effect should be considered when dating units older than the youngest basin, Orientale, or units located close to large craters. Applying our model to the Apollo 16 landing site, we found that 10% of the Apollo 16 regolith may be of Orientale origin, which is almost the same as those of Imbrium (9%) and Serenitatis ejecta (10%). The most abundant basin ejecta in Apollo 16 regolith is from the Nectaris basin (23%). These results provide important constraints for interpreting the provenance of the Apollo 16 samples.