The Global Boundary Stratotype Section and Point (GSSP) for the base of the Bathonian Stage is proposed at the base of limestone bed RB071 (bed 23 in Sturani 1967) in the Ravin du Bès Section (43º57’38’’N, 6º18’55’’E), Bas-Auran area, in the Chaudon-Norante commune, around 25 km at the South-Southeast of Digne-les-Bains, in the “Alpes de Haute Provence” French department. The Ravin du Bès Section, as formal candidate GSSP for the base of the Bathonian Stage, satisfies most of the requirements recommended by the International Commission on Stratigraphy (ICS): 1) The exposure extends over 13 m in thickness, comprising more than five metres of fossiliferous levels below and above the boundary. The Bathonian basal bed corresponds to the “Marno-calcaires à Cancellophycus”, is located 7.8 m below the “Terres Noires” Formation and forms part of a transgressive-facies cycle. At the Bajocian-Bathonian transition, no vertical (bio-, ichno- or tapho-) facies changes, stratigraphic gaps or hiatuses have been recorded. There is no evidence of taphonomic condensation (i.e. mixture of fossils of different age or different chronostratigraphic units). Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints in the Bas-Auran area. 2) There is a well-preserved, abundant and diverse fossil record across the boundary interval, with key markers (ammonites and nannofossils) for worldwide correlation of the uppermost Bajocian and Lower Bathonian. The boundary can be characterized by both primary and secondary (auxiliary) biostratigraphic markers. The section appears to be suitable for biostratigraphic study of microfossils, such as foraminifera, but as yet there are no published studies. The base of Bathonian Stage and Zigzag Zone in Bas-Auran corresponds to the first occurrence level of Gonolkites convergens Buckman and the renewal of parkinsonids. This level coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils, as secondary global marker, are present in all beds, enabling documentation of the Bajocian-Bathonian transition. 3) Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate interpretation of an Early Bathonian deepening half-cycle of second order. No data are currently available for strontium isotope (87Sr/86Sr ratio), oxygen isotope (δ18O) or carbon isotope (δ13C) chemostratigraphy. Bajocian and Bathonian deposits have been remagnetized with a steady normal polarity. Volcanogenic deposits suitable for direct radio-isotope dating are not known in the section. 4) The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”, protected under national law as recognised by UNESCO. The Cabo Mondego Section (Portugal), which provides complementary data on the ammonite succession in the Sub-Mediterranean Parvum Subzone and its chronocorrelation with the Northwest European Convergens Subzone, is suggested as the Bathonian auxiliary section and point (ASP) within this GSSP proposal.
|Titolo:||The base of the Zigzag Zone in the Ravin du Bès Section (Bas-Auran, Subalpine Basin, SE France) as the GSSP for the base of the Bathonian Stage|
|Data di pubblicazione:||2007|
|Parole Chiave:||Bathonian Working Group, chronostratigraphy, biostratigraphy, geochronology.|
|Settore Scientifico Disciplinare:||Settore GEO/01 - Paleontologia e Paleoecologia|
|Citazione:||The base of the Zigzag Zone in the Ravin du Bès Section (Bas-Auran, Subalpine Basin, SE France) as the GSSP for the base of the Bathonian Stage / SIXTO R. FERNÁNDEZ-LÓPEZ, GIULIO PAVIA, ELISABETTA ERBA, MYETTE GUIOMAR, MARIA H. HENRIQUES, ROBERTO LANZA, CHARLES MANGOLD, NICOL MORTON, DAVIDE OLIVERO AND DANIELE TIRABOSCHI. - [s.l] : null, 2007.|
|Appare nelle tipologie:||08 - Relazione interna o rapporto di ricerca|