Carnets de Géologie (Apr 2009)
Uppermost Albian biostratigraphy and chronostratigraphy
Abstract
The Albian Stage is the highest chronostratigraphic unit of the Lower Cretaceous Series and underlies the Cenomanian Stage of the Upper Cretaceous Series. The Albian is divided into three substages, each of which is composed of two or three zones based on distinctive and phylogenetically related ammonite assemblages. The uppermost zone of the Upper Albian Substage, the Stoliczkaia dispar Zone, is found in many Western European condensed sections. The ammonite assemblage in the thin glauconitic sandstone near La Vraconne, Switzerland, was defined as the 'Vraconnian Stage' in 1868. However this concept has been little used and was abandoned in 1963 as part of the Cretaceous chronostratigraphic scale. A recent proposal to resurrect and redefine this stage is based on a number of criteria and very detailed and reliable stratigraphic data. A quantitative biostratigraphic analysis of the ammonite ranges in the key sections shows that the proposed subzones of the S. dispar Zone have discordant ranges. Furthermore, the utility of a 'Vraconnian Stage' between the Albian and Cenomanian stages is geographically limited and the concept embraces one of many depositional sequence cycles of the Albian. The reinstatement of a 'Vraconnian Stage' is not recommended.
