Formal ratification of the GSSP for the base of the Calabrian Stage (second stage of the Pleistocene Series, Quaternary System)
Résumé
The Calabrian Stage is now formally defined by the Global Boundary Stratotype Section and Point (GSSP) at Vrica, Calabria, Italy. This GSSP had previously defined the base of the Pleistocene Series. The Calabrian becomes the second stage of the Pleistocene Series and Quaternary System, following the Gelasian. The GSSP occurs at the base of the marine claystone conformably overlying sapropelic bed 'e' within Segment B in the Vrica section. This lithological level represents the primary marker for the recognition of the boundary, and is assigned an astronomical age of 1.80 Ma on the basis of sapropel calibration. It coincides with the transition from Marine Isotope Stage 65 to 64, and the underlying sapropel bed 'e' is assigned to the Mediterranean Precession-Related Sapropel layer 176. Secondary markers include calcareous plankton bioevents of widely distributed taxa. The boundary falls between the highest occurrence of Discoaster brouweri (below) and the lowest common occurrence of left-coiling Neogloboquadrina pachyderma (above), and below the lowest occurrences of medium-sized Gephyrocapsa (including G. oceanica) and Globigerinoides tenellus. The top of the Olduvai Subchron is identified c. 8 m above the GSSP. Ratification of the Calabrian Stage effectively completes the Lower Pleistocene Subseries.