Global Stratotype Section and Point (GSSP)

Abstract

The relative geological timescale is a hierarchical classification based on a chronostratigraphic scale that consists of units that range from eonothems to stages. More than 150years of development of the chronostratigraphic scale included the naming of numerous stages, many of which overlap each other temporally and/or are only of very local applicability. During the 1960s the International Commission on Stratigraphy of the International Union of Geological Sciences set out to standardize a set of global stages. This began with the use of boundary stratotypes to define chronostratigraphic units, and, in the 1980s, these came to be called GSSPs (global stratotype sections and points). The GSSP is a point (stratigraphic level) in a specific location (stratigraphic section) that defines the base of a stage. The GSSP is correlated by a primary signal, usually a biostratigraphic datum, and by secondary signals—biostratigraphic, chemostratigraphic, magnetostratigraphic, and radioisotopic, among others. The GSSP is not placed at an unconformity or at a lithologic change, so it is at a stratigraphic level of “continuous” sedimentation. GSSPs go through a formal process of proposal and ratification by the voting of earth scientists as specified by the procedures of the International Commission on Stratigraphy. The GSSP method is not above criticism but has done much to standardize chronostratigraphy. Approximately two-thirds of the Phanerozoic stage-base GSSPs (65 of 100 in 2018) have been ratified.