The Silurian of the Moncorvo synclinorium (NE Portugal): biostratigraphy and paleogeographical importance.

Limestones from the Silurian succession of the Moncorvo synclinorium (NW Ce ntral 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 Pseudoo neotodus beckmanni indicate the Ludlow s.l. (or also possibly the late or l atest Wenlock). In the second, Oulodus elegans, O. cf cristagalli and Ozark odina ex gr. remscheidensis indicate a Pridolian age, which is confirmed by the presence, in the same level, of cirrus-type loboliths of scyphocrinoid s. Graptolites from the black-shales with nodules that underlie the limesto nes indicate the existence of Llandovery (Aeronian to Telychian) and Wenloc k deposits. The Silurian succession from Moncorvo thus appears as a condens ed sequence, especially similar to those of the Ossa Morena Zone, Sardinia and parts of North Africa. These successions clearly differ from those whic h characterize the central and southern parts of the Central Iberian Zone, where shallow-water uppermost Silurian deposits are much thicker and compri se abundant coarser terrigenous material. These data suggest that, during t he Silurian, the northwestern part of the Iberian Peninsula (including part of the West Asturian-Leonese Zone) belonged to a special paleogeographic d omain with deeper distal shelf characteristics.