All Title Author
Keywords Abstract

Les Phylloceratoidea (Ammonoidea) aptiens et albiens du bassin vocontien (Sud-Est de la France) [Aptian and Albian Phylloceratids (Ammonoidea) from the Vocontian Basin (SE France)]

Keywords: Ammonites , Phylloceratoidea , Cretaceous , Aptian , Albian , France , Vocontian Basin.

Full-Text   Cite this paper   Add to My Lib


More than 2,200 pyritized ammonites of the Superfamily Phylloceratatoidea have been collected in consonance with the scale of the ammonite zonation of the expanded Marnes Bleues Fm in the Vocontian Basin (SE France). This abundant material allows the description and the figuration (specimens and sutures) of 28 taxa of which 4 are new: * Phylloceras (Hypophylloceras) moriezense Sayn, 1920 subsp. tenuicostulata nov. Diagnosis: variant of P. (H.) moriezense distinguished by a subrectangular section of the whorl and a flattening of the sides less accentuated than on the typical form, with a very fine costulation that descends almost to the middle of the side (early late Aptian); * Phylloceras (Goretophylloceras) vocontium nov. sp. Diagnosis: thick shell, convex sides, rounded and compressed venter, maximum thickness of the whorl near the umbilicus, open umbilicus, constrictions at least at the beginning of the last whorl, oval whorl section, suture line of subgenus Goretophylloceras (mid middle Aptian to earliest Albian); * Salfeldiella (Gyrophyllites) falloti nov. sp. Diagnosis: shell with a finely costulate test, smooth internal mold, open umbilicus, nearly flat sides, rounded venter, subquadratic whorl section, proverse constrictions of the internal mold, radial constrictions in small specimens, a ventral sinus in the largest specimens, suture line like that of the genus Gyrophyllites (late Early Aptian to late Aptian); * Phyllopachyceras brehereti nov. sp. Diagnosis: thick shell, flat sides, venter flat or slightly convex, whorl quadratic in section, suture lines like those of the genus Phyllopachyceras with tetraphyllic spatulate elongated saddles (early mid-Aptian to early late Aptian).Owing to the abundance of the Phylloceratoidea and the variations of specific diversity in 9 fossiliferous levels ranging in age from the late Early Aptian to the end of the Albian it is possible to identify 3 peaks of abundance: * peak 1 during the early mid-Aptian (base of the Martini zone), * peak 2 near the Aptian and Albian boundary, a few meters below the anoxic Paquier level, * peak 3 during the latest Albian (Blancheti zone).Of these 3 peaks the first is the most important probably because the Vocontian Basin attained its maximum depth during this time. The peaks appear to be correlated with the maximum flooding intervals of depositional sequences. But high sea-levels were not always favourable for the Phylloceratoidea. The very fossiliferous Paquier level, although it took place during a high in sea-level, is characterised by the virtual absence of the deep-wate


comments powered by Disqus