Systematic Lunar Geologic Mapping: Results from Copernicus Quadrangle

The geologic representations and derived histories portrayed in the Apollo-era geologic maps remain relevant but require refinement using modern datasets, geodesy, and analytical environments. As part of a renewed mapping program for the Moon, we describe results of a pilot geologic mapping project of the Copernicus quadrangle. We focused on evaluating the regional geologic history, dataset preparation and delivery, and establishing precedents for renewed mapping efforts. We used geodetically-improved Lunar Orbiter (LO) base mosaics supplemented by Clementine color data and derived maps, topography, and LO-III and -V high and very-high resolution images. Our results include (1) validation of the 1:2.5M map scale for systematic mapping based on the resolution of continuous basemaps, (2) subdivision of crater materials into facies based on combined dominance of morphology and spectral signature, (3) retention of facies indicators in unit name but abandonment of ruled patterns indicative of unit-specific albedo, (4) retention of surface “brightness” stipples using a threshold determined by Clementine “albedo” at 750 nm; (5) improvement of criteria for delineating volcanic vent materials, including domes and dark-halo craters, (6) abandonment of (where not critical) the widespread use of concealed contacts, (7) retention of cross-sections to demonstrate vertical and lateral relationships of stratigraphic horizons, (8) application of a 5 km lower limit on the functional delineation of unit outcrops, (9) application of discrete units and stipples to resolvable, unit-specific impact ejecta (e.g., excavated and redistributed mare material), (10) retention of detailed geologic unit explanations (correlation of map units), using discrete, superposition, time-transgressive, and unconformable relationships. Deliverable products include a revised geologic map (as a peer-reviewed article), a versioned geologic mapping guidebook (as a USGS Open File Report), and a downloadable digital mapping template. These efforts can assist in refining geologic mapping methods for all planetary geologic maps.