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Top down instead of bottom up chronostratigraphic definitions
1  New Mexico Museum of Natural History


Since the 1960s, the Phanerozoic chronostratigraphic scale has been defined/redefined by the method of Global Stratotype Sections and Points (GSSPs). The GSSP method defines stage bases, and, where proximate, equates them to the bases of larger chronostratigraphic units. For example, the GSSP that defines the base of the Fortunian Stage also defines the bases of the Terreneuvian Series, Cambrian System, Paleozoic Erathem and Phanerozoic Eonothem. Indeed, via the GSSP method the term Phanerozoic and its subdivisions above the stage level have no particular significance other than as successively larger “pigeonholes” within which to bin stages. The recognition of a single set of global stages is also one of the cornerstones of the GSSP method, though no stage can be correlated globally because of facies changes, taphonomic biases and/or provincialism. Thus, the concept of global standard stages is an unworkable abstraction that should be abandoned. The bottom-up hierarchical reductionism of the GSSP method has reduced the information of chronostratigraphic classification. Series, systems, erathems and eonothems are conceptually more than just collections of stages. Their bases are marked by significant natural events such as the Cambrian explosion, the end-Permian mass extinction in the ocean, etc., that should play a role in chronostratigraphic definition. The GSSP method thus embodies a reductionism that trivializes the boundaries of chronostratigraphic boundaries larger than stages. Stratigraphers should return to a top down chronostratigraphy that defines chronostratigraphic units larger than stages by significant natural events of global correlateability.

Keywords: chronostratigraphy, GSSP, Phanerozoic, stages