Back وحدة طبقية Arabic Unidad estratigráfica Spanish واحد چینهشناسی Persian Unité stratigraphique French Unit stratigrafi ID 層序単元 Japanese Стратиграфиялық бөлімше Kazakh Geologisk eining NN Geologisk enhet NB Jednostka stratygraficzna Polish
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.
Units must be mappable and distinct from one another, but the contact need not be particularly distinct. For instance, a unit may be defined by terms such as "when the sandstone component exceeds 75%".