Le silurien du synclinoriumde Moncorvo (NE du Portugal): Biostratigraphie et importance paléogéographique

Abstract

Limestones from the Silurian succession of the Moncorvo synclinorium (NW Central Iberian Zone, Portugal) have yielded, in two distinct localities, the first Portuguese Silurian conodonts. In the first locality, Kockelella cf. variabilis, K. cf. absidata, Ozarkodina confluens, Oz. excavata and Pseudooneotodus beckmanni indicate the Ludlow s.l. (or also possibly the late or latest Wenlock). In the second, Oulodus elegans, O. cf. cristagalli and Ozarkodina ex gr. remscheidensis indicate a Pridolian age, which is confirmed by the presence, in the same level, of cirrus-type loboliths of scyphocrinoids. Graptolites from the black-shales with nodules that underlie the limestones indicate the existence of Llandovery (Aeronian to Telychian) and Wenlock deposits. The Silurian succession from Moncorvo thus appears as a condensed sequence, especially similar to those of the Ossa Morena Zone, Sardinia and parts of North Africa. These successions clearly differ from those which characterize the central and southern parts of the Central Iberian Zone, where shallow-water uppermost Silurian deposits are much thicker and comprise abundant coarser terrigenous material. These data suggest that, during the Silurian, the northwestern part of the Iberian Peninsula (including part of the West Asturian-Leonese Zone) belonged to a special paleogeographic domain with deeper distal shelf characteristics.