Stratigraphic unit
VOLUME OF ROCK DEFINED BY ITS PETROGRAPHIC, LITHOLOGIC OR PALEONTOLOGIC FEATURES
Supergroup (geology); Member (geology); Geologic group; Geologic unit; Rock unit; Stratigraphic units; Geological unit; Member (stratigraphy); Unit (geology); Supergroup (stratigraphy)
A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it.