Original paper
Upper Sinemurian–Pliensbachian calcareous nannofossil biostratigraphy of the E Rodiles section (Asturias, N Spain): a reference section for the connection between the Boreal and Tethyan Realms
Fraguas, Ángela; Comas-Rengifo, María José; Goy, Antonio; Gómez, Juan J.
Newsletters on Stratigraphy Volume 51 Number 2 (2018), p. 227 - 244
31 references
published: Mar 10, 2018
ArtNo. ESP026005102003, Price: 29.00 €
Abstract
A total of 129 samples, Late Sinemurian–Pliensbachian in age, were collected from the welldated and expanded E Rodiles section (Asturias, Northern Spain). 5 main events: the first occurrences (FOs) of Crepidolithus crassus, Similiscutum cruciulus, Biscutum novum, Lotharingius hauffii and Lotharingius sigillatus, were identified on the basis of continuously recorded and common taxa. The secondary events are based on taxa with a discontinuous record and are usually rare or extremely rare, especially in their initial and final ranges. They include the FOs of Orthogonoides hamiltoniae, Crepidolithus cantabriensis, Calyculus spp., Bussonius prinsii, Biscutum dubium, Biscutum finchii, Biscutum grande and Lotharingius barozii, and the first common occurrences (FCOs) of Calcivascularis jansae and L. hauffii. All the calcareous nannofossil bioevents recognized in this work are reliable and reproducible in the biostratigraphic scheme previously proposed for the Cantabrian Range, except for the FOs of C. crassus, O. hamiltoniae, C. cantabriensis, Calyculus spp., B. prinsii and B. dubium, which are new here. 3 calcareous nannofossil Zones (CNZs; NJ3, NJ4 and NJ5) and 4 calcareous nannofossil Subzones (CNSzs; NJ4a/b and NJ5a/b), were identified in the E Rodiles section, defining the base of the NJ3 Crepidolithus crassus CNZ for the first time in N Spain. This new biostratigraphical information is compared to schemes from NW Europe, Portugal, N France and Italy/S France. Based on this comparison, we hypothesized that O. hamiltoniae, C. crassus and Calyculus spp could have Boreal affinities, first occurring in the Boreal Realm and spreading later to the Tethyan Realm, when there were predominantly southward currents in the Boreal seawaters. Contrarily, the FCO of C. jansae, which is considered a Mediterranean taxon, is recorded in the lower part of the Margaritatus Ammonite Zone (AZ), when the Tethyan currents were flowing northwards. With respect to other secondary events, discrepancies have been found in the FO of B. prinsii and B. dubium, probably due to the scarcity and high dissolution susceptibility of these taxa.
Keywords
Biohorizons • Calcareous nannofossils • Connection area • Epicontinental seaway • Asturias • Early Jurassic