Pennsylvanian

The name and its history

Henry Shaler Williams (1891) · 1891; USGS Bulletin 80, original source available

What does the word literally mean?

of Pennsylvania. Transmission: American English geological toponym; Pennsylvania, USA. The deeper etymology of the place-name itself is not established by the geology sources cited.

What did the original author mean?

Henry Shaler Williams (1891). Williams proposed a geographical counterpart to Mississippian for a younger Carboniferous rock association conspicuous in Pennsylvania, especially the coal-bearing succession.

Why was the name needed?

The traditional single Carboniferous System covered distinct North American packages: an older, generally carbonate-dominated interval and younger coal-measure-rich formations, often separated by a conspicuous unconformity.

What evidence supported the original concept?

Williams correlated the regional stratigraphy of Pennsylvania with other areas using lithology, fossil successions, superposition and the distribution of coal measures, rather than any global boundary definition.

How has geology changed the concept?

The name later rose to system status in influential American schemes; after internationally ratified changes of 1999–2004 it is a Carboniferous subperiod. Its basal boundary is defined at Arrow Canyon, Nevada, using conodont biostratigraphy, not Pennsylvania coals.

Further historical context

*Original historical meaning. Williams proposed a geographical counterpart to Mississippian* for a younger Carboniferous rock association conspicuous in Pennsylvania, especially the coal-bearing succession.

*Why a new distinction was needed.* The traditional single Carboniferous System covered distinct North American packages: an older, generally carbonate-dominated interval and younger coal-measure-rich formations, often separated by a conspicuous unconformity.

*Evidence and historiographical transformation.* Williams correlated the regional stratigraphy of Pennsylvania with other areas using lithology, fossil successions, superposition and the distribution of coal measures, rather than any global boundary definition.

*Modern ICS interpretation.* The name later rose to system status in influential American schemes; after internationally ratified changes of 1999–2004 it is a Carboniferous subperiod. Its basal boundary is defined at Arrow Canyon, Nevada, using conodont biostratigraphy, not Pennsylvania coals.

Editorial qualification

Pennsylvania is the naming locality, not a literal geological descriptor. Coal-bearing facies are regionally variable.

Related names

Carboniferous · Mississippian · Bashkirian · Moscovian · Kasimovian · Gzhelian · Fossil · Conodont · Stratigraphy · Lithology · Biostratigraphy · Superposition · Facies

Sources

1. ICS International Chronostratigraphic Chart (2026/06) — Official global names, ranks and numerical ages
2. Williams (1891), Correlation Papers: Devonian and Carboniferous, USGS Bulletin 80 — Original nineteenth-century publication; priority claim corroborated in published synthesis
3. U.S. National Park Service, historical Mississippian–Pennsylvanian summary — Secondary attribution to Winchell (1870) and Williams (1891)
4. Heckel & Clayton (2006), The Carboniferous System: use of new official names — Authoritative published explanation of the 1999–2004 international renaming
5. ICS Subcommission on Carboniferous Stratigraphy: ratified GSSPs and pending boundaries — Status of internationally ratified boundaries; proposed markers are provisional
6. Waters et al. (2009), BGS Carboniferous successions of southern Great Britain — British regional units, coal measures and differences from global nomenclature