|mhorn||Дата: Friday, 12.10.2012, 23:19 | Сообщение # 1|
|Sassaroli S., Venturi F. (2012) Early Toarcian (post-OAE) Hildoceratinae (Ammonitina) fauna from the Marchean Apennines (Italy) // Revue de Paléobiologie, Genève, Vol. 31, no.1. P.85-114. |
The Apennines (Italy) outcrop of the Marconessa quarry yielded a very interesting ammonite fauna of early Toarcian. Here the ammonite Hildaites (early Hildoceratinae) radiation is recorded after the black shales of the OAE. The earliest forms of this genus, which are useful as indexes for West Tethyan zonation, were found in assemblage with very rare Dactylioceras (Orthodactylites), which in NW Europe are suitable as indexes of the Tenuicostaum zone. The early Toarcian West Tethyan standard zonation is however questioned because the accepted indexes H. serpentinus and H. levisoni are unsuitable for the Apennines zonation and correlations. Elsewhere
the authors proposed for the local Apennines zonation H. striatus and H. undicosta as indexes, being chiefly the former widespread in the West Tethyan Province. Furthermore, Hildoceratids were affected by a some degree of provincialism, which makes hard detailed correlations. On the other side, Dactylioceratids were cosmopolitan, so that they are more useful to correlate the West Tethyan and NW European Provinces. These Apennines biostratigraphical data seem to suggest that the maximun of extinction and recovery of the ammonite fauna across the OAE must be placed in the Tenuicostatum zone. New Hildaites taxa are here proposed, such as H. evolutus, H. planiventris, H. bisulcatus and H. calamantis.
Middle Jurassic - Lower Cretaceous ammonites & aptychi