Les Ammonites du Pliensbachien des Pyrénées ariégeoises (Zone nord-pyrénéenne, France) : taxonomie, stratigraphie et implications paléogéographiques

The Pliensbachian Ammonites of the Pyrenees in Ariège (North-Pyrenean Zone). Taxonomic and stratigraphic studies. Palaeo­geographic implications. - We describe in this work the rich ammonite fauna provided by the Pliensbachian of several localities in the hinterland of Foix (Ariège, France). The stratigraphy of Pliensbachien Ariège is specified and completed by multiple cuts made on the sedimentary cover of the Paleozoic massif of Arize (North Pyrenean Zone). The sedimentological, palaeoecological and palaeogeographic contexts are presented. Forty-nine distinct ammonite taxa are described and illustrated, one of which is new Uptonia schlatteri nov. sp. Their vertical distribution has identified 18 distinct paleontological horizons (zonules) that can be correlated with the standard biozonation used in the Northwestern European Bioprovince. With the exception of two ubiquitous taxa [Lytoceras fimbriatum (J. Sowerby, 1817) and Radstockiceras gemmellaroi (Pompeckj, 1907)], the ammonites collected in Ariège all relate to the fauna found most often in northwest Europe, which predominated in the Iberian and Aquitaine regions. Some of these taxa, such as the genera Metaderoceras and Fuciniceras, are particularly associated with the southern part of the European platforms, thus giving a "southern" accent to these ammonite associations. At shallow depth, since they were located on the margin of an important shoal area (a submerged ridge, the Occitan Shoal in the present case), the Ariège sedimentation zone contains a remarkable diversity of Pliensbachian ammonites, due to multiple biotopes. Located on the borders of a stable Europe and Iberia, it further benefits from an exceptional paleogeographic location, being on a wildlife corridor between the Aquitaine Plain and the Iberian river basins whose richness in biodiversity is evident.