Multiringed basins - Illustrated by Orientale and associated features

Abstract

Geologic mapping and photographs of the Orientale multiring basin are studied as to origin, size, and nature and distribution of ejecta. Six facies of ejecta are observed around the Cordillera Mountains: concentric, radial, smooth plains, grooved, secondary impact craters, and fissured. Transport of these ejecta occurred by block gliding, landsliding, debris flow, and possibly by base surge, viscous flow, and ballistic ejection. The ejecta are mainly clastic types, but melts and annealed breccias are expected to be abundant. Mixing of ejecta and substrate materials must have occurred; compositions of the ejecta are probably zoned laterally and vertically.