Floral remains from the highest Valdeón formation, a marine stephanian unit south of the Picos de Europa, and comparisons with eastern Asturias, NW Spain

Resumen

A critical analysis is presented of the available data on the Valdeón Formation, a Stephanian unit southwest of the Picos de Europa, in northern Leon. It lies unconformably on Devonian and lower Carboniferous (Mississippian) strata of the Gildar-Montó nappe structure, and is overthrust from the northwest by a variety of older strata of the Ponga unit. The Valdeón Formation, consisting of mudstones, sandstones and lensing conglomerate bands, is largely unfossiliferous and probably marine up to the highest levels where possibly lagoonal deposits contain a drifted megafloral assemblage, which is of Barruelian or later age. This flora is documented here with illustrations and the various taxa are discussed. Comparison is made with a succession of upper Cantabrian and lower Barruelian strata in northern Palencia (Brañosera and Barruelo formations), which show a broadly similar stratigraphic development. Floras from a small terrestrial interval near the base of the predominantly marine strata of Stephanian B age in eastern Asturias (at Fontecha and Arenas de Cabrales) are discussed for the overall comparison, but these floras are later in age and the relevant strata, belonging to the post-Asturian basin, show a different development. These later Stephanian floras are listed but only two species are illustrated.