Calcareous nannofossils of the uppermost Bedoulian and lower Gargasian of La Tuilière - St-Saturnin-lès-Apt (area of the Aptian stratotype, Vaucluse, SE France)

Abstract

An 148 m composite section located in the Gargas area stratotype in southeastern France has been studied for its calcareous nannofossil content. The four sections span the upper Bedoulian to lower Gargasian with the stadial boundary located within the basal section south of the village of Clavaillan. A total of 75 samples was processed to inventory taxonomy and stratigraphic distributions. Eprolithus floralis is present at the base of the stratigraphic succession. The lowest occurrence of this species, which marks the base of Subzone NC7A, has been documented in the uppermost lower Aptian (Bedoulian) in other sections in southeastern France. The highest occurrence of the genus Micrantholithus has been utilized to delineate the base of Subzone NC7B. This subzonal boundary was placed at 48 m in the Les Gays I section (113.5 m in the composite) below the lowest occurrence of the foraminifer Globigerinelloides ferreolensis in the suprajacent sample (50 m). The lowest occurrence of Braarudosphaera africana is identified as a regional biohorizon in lower Subzone NC7A and a local proxy for the Bedoulian/Gargasian boundary. This event was placed at 15.5 m in the Clavaillan section at the base of the Dufrenoyia furcata Zone and within the "Niveau Blanc inférieur" marker bed (NB1). The genus Nannoconus is abundant to very abundant in all samples examined. Taxonomic rigor has resulted in the recognition of five main morphologic groups (A-E), including all but one of the 15 species discriminated over this relatively short stratigraphic interval. Four main Nannoconus assemblage biozones - with one subdivision - have been distinguished through semi-quantitative analyses and organized relative to these taxonomic groupings. Assemblage Biozone B is restricted to the Bedoulian and has been correlated to the lower portion of Subzone NC7A (i.e., NC7A1). Assemblage biozones GI and GII (A-B) have been correlated to the upper portion of Subzone NC7A (i.e., NC7A2) and Biozone GIII to Subzone NC7B within the Gargasian. Assipetra is another solution-resistant genus included in semi-quantitative analyses, where both its species were separated into small and large forms based on a size of 10 μm. The highest percentages of large morphotypes are within the Bedoulian in the lower 10.5 m of the Clavaillan section, roughly coeval to an acme of large Assipetra observed in the basal portion of the Serre Chaitieu section in the nearby Vocontian Basin.