List of Global Boundary Stratotype Sections and Points
This is a list of Global Boundary Stratotype Sections and Points. Since 1977, Global Boundary Stratotype Sections and Points (abbreviated GSSPs) are internationally agreed upon reference points on stratigraphic sections of rock which define the lower boundaries of stages on the geologic time scale.
Source: Wikipedia — List of Global Boundary Stratotype Sections and Points (CC BY-SA 4.0)