The base of the Pennsylvanian Sub-System (Upper Carboniferous) and Bashkirian Stage is located at Arrow Canyon near Las Vegas, Nevada, in the arid Basin and Range Province of the southwestern USA. The GSSP is located at 82.9m above the top of the Battleship Formation in the lower Bird Spring Formation at the evolutionary first appearance of the conodont Declinognathodus noduliferus s.l. The GSSP coincides exactly with the historically stable Mississippian-Pennsylvanian boundary.
The Mid-Carboniferous Boundary is located at Arrow Canyon in the southwestern United States approximately 75km NE of Las Vegas, Nevada, on land administered and protected by the Federal Government. It is readily accessible by a 4-wheel drive road that runs along Arrow Canyon and is connected to Highway 168 by a paved secondary road.
During the Carboniferous Arrow Canyon was situated near the paleo-equator in a tropical to subtropical seaway extending from SE California through western Canada to Alaska.
The Birdspring Formation comprises limestone with subordinate mudstone, sandstone and dolostone. The boundary limestone from 6.95m to 8.1m comprises grainstone and packstone dominated by pelmatozoans, brachiopods and bryozoans; above 8.1m brachiopod packstone to wackestone is predominant.
The Mid-Carboniferous Boundary is at 7.63m.
The succession containing the boundary interval comprises numerous high-order transgressive-regressive (TR) sequences that resulted mainly from glacio-eustatic fluctuations driven by ongoing glaciations in Gondwana.
The Bashkirian GSSP coincides with the evolutionary first appearance of the conodont Declinognathodus noduliferus s.l.
The Rhipidomella nevadensis brachiopod zone is latest Mississippian in age and extends to the GSSP boundary where it is overlain by the Rugoclostus zone of early Pennsylvanian age.
Conodont FAD Declinognathodus noduliferus