Article: The ammonite fauna of the Calcaire à Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France)
The Calcaire a Baculites of the Cotentin Peninsula, Manche, France, is a sequence of bioclastic limestones occurring as isolated outliers resting unconformably on rocks of Precambrian to Cenomanian age. Ammonites, chiefly Baculites, are locally abundant, and their taxonomy is revised. B. anceps Lamarck, 1822 dominates the fauna, with scarce Hoploscaphites constrictus (J. Sowerby, 1817) and rare to very rare Pachydiscus (Pachydiscus) gollevillensis (d'Orbigny, 1850), P. (P.) jacquoti Seunes, 1890, P. (P.) sp., P. (Neodesmoceras) mokotibense Collignon, 1952, Anapachydiscus fresvillensis (Seunes, 1890), Hoplitoplacenticeras lasfresnayanum (d'Orbigny, 1841), Glyptoxoceras sp., Diplomoceras cylindraceum (Defrance, 1816), B. vertebralis Lamarck 1801, Fresvillia constricta gen. et sp. nov., Hoploscaphites sp., and Acanthoscaphites verneuilianus (d'Orbigny, 1841).Limited belemnite and echinoid data, published observations on bryozoans and forams, and the known ranges of some of the key ammonites in the type area of the Maastrichtian and environs and in the White Chalk facies of northern Europe all place the unit in the Upper Maastrichtian; the balance of evidence suggests it is equivalent to the upper Belemnitella junior Zone and part of the Belemnella casimirovensis Zone. Some localities extend very high in the casimirovensis Zone on the basis of the occurrence of late forms of H. constrictus ('variety' crassus of authors); there is no positive evidence for the Lower Maastrichtian from the ammonite fauna.