A stratotype is the original or a subsequently designated standard correlative type section or boundary of a named stratigraphic unit or stratigraphic boundary. In a particular stratigraphic sequence, a stratotype represents a particular interval or a particular reference exposure of strata. It constitutes a criterion for defining and identifying the stratigraphic unit’s location or the stratigraphic boundaries. This interval is the unit stratotype of the stratigraphic unit, and the specific reference point is the boundary stratotype. A chronostratigraphic stratotype relies on the boundary stratotype to be defined, whereas a lithostratigraphic stratotype mainly depends on the unit stratotype.