Orientale Ejecta at the Apollo 14 Landing Site Implies a 200-million-year Stratigraphic Time Shift on the Moon

Abstract

Abstract Detailed spectral mapping, cratering statistics, and impact basin ejecta column estimates document a new and very different stratigraphic relationship for the Apollo 14 landing site. We observe a resurfacing event in the crater size–frequency distribution in agreement with a single blanketing layer. Using the crater size–frequency distribution, we determine two relative ages (cumulative crater frequencies) that match those observed for the Imbrium and Orientale basins, respectively. The pattern and strength of resurfacing and morphological distinction by spectral features suggest the top layer to be about 10–25 m thick. We propose that this top layer at the Apollo 14 landing site is Orientale basin ejecta above Imbrium basin ejecta. Such stratigraphy reattributes the (majority of) Apollo 14 samples to Orientale rather than to Imbrium basin and implies that Orientale basin is about 3.92 Gyr old, 200 million years older than previously suggested. The youngest lunar basin thus formed at the onset, rather than amid, of recorded mare volcanism. This time shift also changes constraints on early planetary and solar system processes, such as the intensity of impact bombardment, and pleads for revision of the crater-statistics-based surface ages of other planetary bodies.