Ordovicien supérieur

OBS: upper: Pertaining to rocks or strata that are normally above those of earlier formations of a chronostratigraphic unit (system, series, stage) to indicate position in the geologic column and corresponds to ""late"" as applied to the name of the equivalent geologic-time unit ... The initial letter of the term is capitalized to indicate a formal subdivision ... and is lowercased to indicate an informal subdivision ...