THE CHRONOSTRATIGRAPHIC NOMENCLATORIAL HISTORY OF THE PENNSYLVANIAN: SERIES TO SYSTEM TO SUBSYSTEM

Henry Shaler Williams, in 1891, proposed the Pennsylvanian as a series-level division of the Carboniferous System for the North American geologic time scale. Some later publications on the history of that time scale have credited the proposal of the name to J. J. Stevenson in 1888. While Stevenson did not originate the name Pennsylvanian, recognizing H. S. Williams as its author himself, he did elevate the interval to system status in 1907, although without discussion. That usage was adopted by the U. S. Geological Survey in 1924, but not published until 1925. Thus, the Pennsylvanian became the last named system/period division of the geologic time scale in common usage by North American stratigraphers. Internationally, European stratigraphers began using Pennsylvanian as early as 1950 (i.e. Jongmans and Pruvost), although the name was not formally recognized by the U. S. Geological Survey until Bradley in 1953, with an apparent reminder published in 1956. The DNAG Geologic Time Scale published by the Geological Society of America in 1983, included both Carboniferous and Mississippian-Pennsylvanian as periods, but the International Stratigraphic Chart, published by the International Commission on Stratigraphy (ICS) as of 2017 (and as far back as 2008), has moved the Carboniferous and the Mississippian-Pennsylvanian System columns so that the boundary line separating System and Series nomenclature does not indicate that the Mississippian and Pennsylvanian are regarded as series. That point, however, becomes moot, since the International Chronostratigraphic Chart, under the aegis of the ICS, in 2004 reduced both Mississippian and Pennsylvanian to global sub-systems of the Carboniferous System.