Proposal for the recognition of a Saberian Substage in the mid-Stephanian (West European chronostratigraphic scheme)

Abstract

A proposal by WAGNER & ALVAREZ-VAZQUEZ (2010) to recognise a Saberian Regional Substage to follow upon Barruelian is now formalised with reference to a boundary stratotype in the Sabero Coalfield (Leon), NW Spain. A brief historical perspective on the Stephanian substages (formerly stages) confirms the inadequacy of the classical A, B and C subdivision recognised in the intramontane basins of the Massif Central, France. The lower Stephanian succession in the Cantabrian Mountians, NW Spain, where it is in continuity with the highest Westphalian and shows both marine and terrestrial facies, has already provided suitable stratotypes for the Cantabrian and Barruelian substages. A Barruelian–Stephanian B boundary was recognised in the Sabero Coalfield, NW Spain, in correlation with the putative Stephanian A–B boundary identified in the Carmaux Coalfield, south-central France. This boundary lies below the base of type Stephanian B as defined in the Saint Etienne Basin. A Saberian Substage following upon Barruelian and occupying the gap below the Stephanian B at Saint Etienne is now formalised by a proposed stratotype at Sabero. Palaeobotanical analysis confirms that the Saberian is broadly equated with the Alethopteris zeilleri Megafloral Zone. The proposed stratotype is described in the context of a coastal basin with westerly onlap both within and beyond the Sabero Coalfield. Pyroclastic tonsteins in the reference Saberian succession of Sabero have permitted radiometric U-Pb dating of zircons (CATIMS) from two bands at around 302 Ma. A preliminary account of the absolute age analysis is given.