Geologic history of the south circumpolar region (SCR) of the Moon

Abstract

Space exploration missions have placed renewed focus on the South Circumpolar Region (SCR) of the Moon due to its unexplored nature by landed missions, potential water resources, proximity to the ancient South Pole-Aitken (SPA) basin, and the presence of regions that provide near-permanent solar illumination. Unlike previous surface exploration sites, the SCR lacks extensive mare regions and is most similar to the Apollo 16 and Luna 20 sites, and is dominated by overlapping deposits of impact craters and basins of a wide range of sizes and ages. This renders the geologic history of individual regions difficult to determine, and the provenance of returned samples potentially enigmatic. In order to help alleviate these problems and to provide a consistent geological framework for landing site selection, mission planning and operations, and interpreting sample provenance, we have compiled a new geologic map of the SCR (1:300000 mapping scale; South pole to 70°S) using the most recently acquired orbital data (LRO LROC WAC 100 m/pix resolution image data and LOLA-based 80–20 m/pix resolution DTMs), and portraying geological units, features and structures, stratigraphic sequences, and providing a framework to address many outstanding problems in lunar science. We define and map several major types of units and structures: (1) high-standing massifs of the SPA basin, (2) crater-related units – walls, rims, and ejecta of impact craters and smaller basins, (3) plains units of both impact (impact melt and/or Cayley Formation) and volcanic origins (lava fields and pyroclastic deposits) and (4) landforms related to degradation of crater topography. Absolute Model Ages (AMAs) derived from crater size-frequency distribution (CSFD) measurements for ∼200 of these units/structures, whose relative ages were determined by superposition relations, were used to compile a correlation of map units for the SCR region.