%0 Journal Article
%A Pavia, Giulio
%A Fernández López, Sixto Rafael
%A Mangold, Charles
%T Ammonoid succession at the Bajocian-Bathonian transition in the Bas Auran area, Digne district, South-East France.
%D 2008
%@ 0035-6883
%U https://hdl.handle.net/20.500.14352/50920
%X The uppermost Bajocian to lowermost Bathonianammonoid succession has been studied in the Bas Auran area in viewof choosing one of its sections as the Global Stratotype Section andPoint (G.S.S.P.) of the Bathonian Stage. The Bas Auran ammoniteassemblages display exceptional values of record quality. The stratigraphicdistribution of 629 specimens referred to 63 species and 35genera, collected during the last forty years from three sections (Ravindu Bès, Ravin d'Auran, Ravin des Robines), is plotted and analyzed,bed by bed. Over 85 stratigraphic levels, through 9 m in thickness,have been studied at the top of the "Marno-calcaires à Cancellophycus"formation, ranging from the latest Bajocian (Parkinsoni Zone,Bomfordi Subzone) to the earliest Bathonian (Zigzag Zone, ConvergensSubzone) and the base of the Macrescens Subzone. Ammonoidassemblages are composed of Northwest European and Mediterraneanelements, associated with Sub-Mediterranean ones, allowing chronocorrelationbetween the Northwest European Convergens Subzoneand the Sub-Mediterranean Parvum Subzone. The basal boundaryof the Zigzag Zone and of the Bathonian Stage is placed at the baseof Sturani's bed 23 in the Ravin du Bes section and is identified by thefirst occurrence of Gonolkites convergens, and coincides with the loestoccurrence of Morphoceras parvum. Features of the ammonoidsuccession indicate relatively homogeneous and good record quality,gradual biostratigraphic change and high degree of taxonomic similaritybetween the Bomfordi and Convergens subzones. Palaeontologicalcriteria also indicate relatively high values of palaeontologicaland stratigraphic completeness at the base of levels RB070-RB071(= level 23 in Sturani 1967) which corresponds to the Bajocian/Bathonianboundary. The Ravin du Bès Section, with forty-six successiveammonoid fossil-assemblages of the Convergens Subzone belongingto three biohorizons through five metres of thickness, shows maximumvalues of biostratigraphic and biochronostratigraphic completeness,being one of the most complete in the world. Therefore, theRavin du Bès Section should be chosen as the Global Stratotype Section and Point for the base of the Bathonian Stage. Two biostratigraphiclogs summarize the ammonite content from the uppermostBomfordi to basal Macrescens subzones. Three plates illustrate themost characteristic ammonoid taxa at the Bajocian-Bathonian passagein the Bas Auran succession.
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