First biostratigraphical constraints on the pre-Upper Ordovician sequences of the Pyrenees based on organic-walled microfossils

The first age constraint on the upper part of the pre-Upper Ordovician series of the Pyrenees is presented. Data are based on acritarchs from the Jujols Group in the La Molina area on the southern slope of the Canigo massif, near the Upper Ordovician unconformity. The new data allow us to attribute a Late Cambrian (Furongian) to Early Ordovician age to the upper part of the Jujols Group and to support the absence of well developed Middle Ordovician strata in the Pyrenees. Our results confirm the occurrence of an Upper Ordovician unconformity and highlight the Sardic affinity of the pre-Upper Ordovician sequences in the Pyrenees. These sequences differ markedly from the pre-Upper Ordovician series of the Iberian Massif. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.