The end of the stage is defined by the last magnetic pole reversal (781 ± 5 Ka) and plunge into an ice age and global drying possibly colder and drier than the late Miocene (Messinian) through early Pliocene (Zanclean) cold period.
Because sea shells are much more abundant as fossils, 19th- and early-20th-century geo-scientists used the plentiful and well-differentiable Mollusca (mollusks) and Brachiopods to identify stratigraphic boundaries.
By 1948 scientists used the initial appearance of cool-water (northern) invertebrate faunas in Mediterranean marine sediments as the beginning marker for the Calabrian.
However, it was discovered that the original type section was discontinuous at that point and that the base of the Calabrian Stage as defined by fauna assemblages extended to earlier levels within the Pleistocene.
[7] The beginning of the Calabrian hence is defined as: Just above top of magnetic polarity chronozone C2n (Olduvai) and the extinction level of calcareous nannofossil Discoaster brouweri (base Zone CN13).