Los nanofósiles calcáreos del jurásico inferior de la sección de E rodiles (Asturias, España). Implicaciones bioestratigráficas y paleoecológicas

Zusammenfassung

129 samples, Upper Sinemurian-Pliensbachian in age, were collected from the East Rodiles section, which is well- dated with ammonites and crops out in a coastal cliff located on the eastern part of the Rodiles Cape, in Asturias (Northern Spain). 5 main events: the first occurrences (FOs) of Crepidolithus crassus, Similiscutum cruciulus, Biscutum novum, Lotharingius hauffii and Lotharingius sigillatus, based on continuously recorded and common taxa, and 8 secondary events: the FOs of Orthogonoides hamiltoniae, Bussonius prinsii, Biscutum dubium, Biscutum finchii, Biscutum grande and Lotharingius barozii, and the first common occurrences (FCOs) of Calcivascularis jansae and L. hauffii, on the basis of rare taxa with a discontinuous record, were identified. Excluding the FOs of C. crassus, O. hamiltoniae, B. prinsii and B. dubium, the other calcareous nannofossil bioevents recognized in this work are reliable and reproducible with the biostratigraphic scheme previously proposed for the Cantabrian Range. 3 calcareous nannofossil Zones (NJ3 Crepidolithus crassus, NJ4 Similiscutum cruciulus and NJ5 Lotharingius hauffii), 4 calcareous nannofossil Subzones (NJ4a Crepidolithus cantabriensis, NJ4b Biscutum novum, NJ5a Biscutum finchii and NJ5b Lotharingius sigillatus), were identified in the East Rodiles section. This biostratigraphic framework is compared to schemes from NW Europe, Portugal and Italy/S France. The FO of S. cruciulus is reproducible in all the compared areas. However, the FOs of C. crassus, L. hauffii and L. sigillatus seem to be diachronous events in the Boreal and Tethyan Realms. In Portugal and Italy/S France, the FO of C. crassus is located around the Oxynotum/Raricostatum AZ (Ammonite Zone) boundary and within the Raricostatum AZ, respectively, whilst in NW Europe, this event lies around the Obtusum/Oxynotum AZ boundary and within the Obtusum AZ in this work. It could confirm the Boreal affinities of C. crassus. In the same way, it is possible that the FO of L. hauffii recognized in Italy/S France within the Spinatum ammonite Zone could be correlated with the FCO of L. hauffii identified in this work. Probably the Lotharingius species firstly appeared in the Boreal Realm, and later spread into the Tethyan Realm.