Mid-Carboniferous Boundary Stratotype for Europe
As part of an initiative set up in the mid 1980’s by the International Subcommission on Carboniferous Stratigraphy (Mid Carboniferous Working Group), the locality of Stonehead Beck in Cowling, north Yorkshire was proposed as a possible site for the international chronostratigraphic type section for the Carboniferous Period. For 10 years a number of global sites were considered. Eventually Arrow Canyon, located near Las Vegas, Nevada, in the arid Basin and Range Province of the southwestern United States, was chosen to be the Global Boundary Stratotype Section and Point (GSSP) for the Mid-Carboniferous Boundary. The GSSP was been approved in January 1996. Stonehead Beck, Cowling, North Yorkshire had been the European candidate. It is now condsidered to be the European type section for the MCB interval.
For subsystems, the terms Mississippian and Pennsylvanian should be used in all regions of the world to replace the more ambiguous and more awkward terms Lower and Upper Carboniferous. Regional geographic names for series and stages may continue to be used in those regions in which they developed, specifically in Western Europe, the USA, and China. However, their global equivalents should be denoted equally, particularly as they become better correlated, in order to facilitate global correlation in future work. New stage names include Serpukhovian, Bashkirian, Moscovian, Kasimovian and Gzhelian. The Neville George stage names, Courcey to Westphalian, are now relegated to regional substage status. The table below summarises the main changes.
Stonehead Beck in Cowling, north Yorkshire lies within the Sabden Shales at the northwestern end of the Pendle Monocline and spans the Eumorphoceras - Homoceras ammonoid Genus-Zone. Sabden Shales represent the time when hemipelagic muds were deposited in relatively anoxic deep water of the Bowland Sub-Basin (Craven Basin). Fully marine conditions are marked by marine bands dominated by a diagnostic thick-shelled ammonoid fauna.
The Mid-Carboniferous boundary has been defined at the first entry of the conodont Declinognathodus inequalis about 9.4 metres above the Arnsbergian/Chokerian boundary and significantly is marked by a major mass extinction of faunas. Perhaps the mass extinction was triggered by the collision of Gondwana and Laurasia.
Sabden Shales Outcrop in Stonehead Beck
Photo: © Paul Kabrna 2009