Rethinking the Carboniferous Chronostratigraphic scale

摘要

The Carboniferous chronostratigraphic scale is a hierarchy of two subsystems, six series and seven stages developed during nearly two centuries of research. The first geological studies of Carboniferous rocks began in Europe in the late 1700s. In 1822, based primarily on the work of William D. Conybeare, he and William Phillips coined the term Carboniferous for the coal-bearing strata, and some underlying strata, in Great Britain. Recognition of the Carboniferous elsewhere soon followed. Carboniferous series and stage nomenclature developed mostly between 1870 and 1950, with the proposal of numerous regional stages/ substages based primarily on paleobotanical, foraminiferal and ammonite biostratigraphy (as well as some brachiopod and coral biostratigraphy) in Western Europe, the former Soviet Union, China and the USA. From the regional stages, seven "global stages" of the Carboniferous chronostratigraphic scale have been identified (in ascending order): Tournaisian, Visean, Serpukhovian, Bashkirian, Moscovian, Kasimovian and Gzhelian. The work of the Subcommission on Carboniferous Stratigraphy to standardize and define the Carboniferous chronostratigraphic scale began in the 1950s. The 1980s saw the rise of Carboniferous conodont biostratigraphy, and three of the four ratified GSSPs relevant to the Carbnferous chronostratigraphic scale use conodont evolutionary events as the primary signal for correlation - bases of the Tournaisian (base of Carboniferous), Bashkirian (base of Pennsylvanian) and Asselian (base of Permian/top of Carboniferous). The GS SP for the base of the Visean has a foraminiferal biotic event as its primary signal. Issues in the development of a Carboniferous chronostratigraphic scale include those of the rank of chronostratigraphic units, provinciality, and the use of conodonts in chronostratigraphy. The following changes are recommended to the current Carboniferous chronostratigraphic scale: (1) abandon the "global" subsystems Mississippian and Pennsylvanian; (2) abandon the current Carboniferous series as uninformative, and elevate the currently recognized stages to series; (3) acknowledge that there are no Carboniferous global stages and use the four established regional chronostratigraphic schemes - American, Westen European, Russian and Chinese - as equally useful sets of series and stages; (4) raise the Western European (primarily Belgian and British) susbstages to stages and use them as the primary set of Carboniferous stages; and (5) stop trying to use conodonts in Carboniferous chronostratigraphic definitions. We need to step backward to the Carboniferous chronostratigraphy recommended by the Subcommission on Carboniferous Stratigraphy in 1997, which is a more detailed, useful and realistic Carboniferous chronostratigraphy than the current scheme.