Identification of a Romaniceras (Romaniceras) marigniacum sp. nov. ammonite biohorizon (Middle Turonian) at the base of the Tuffeau Jaune de Touraine (France).

In the south of the Paris Basin, along the Loire and Cher valleys, the Tuffeau Jaune de Touraine Formation was traditionally attributed to the Late Turonian by the presence of rare Romaniceras deverianum (ORBIGNY, 1841). Moreover, the several metres of tempestites at the base of the formation never yielded ammonites. Today, in southern Touraine, more than 150 ammonites were collected from the base of the Tuffeau Jaune de Touraine and in the highest part of the underlying Tuffeau de Bourre bring new significant data: the lower part of the Tuffeau Jaune de Touraine remain in the Romaniceras ornatissimum zone, Middle Turonian in age (Tm 3). Furthermore, the discovery in that biohorizon of the new species Romaniceras (R.) marigniacum AMEDRO & CHATELIER sp. nov. is indicative of the highest part of the R. ornatissimum zone (high Tm3). Other species are associated to the R. marigniacum biohorizon as: Romaniceras (Yubariceras) ornatissimum (STOLICZKA, 1864), Masiaposites cf. kennedyi AMEDRO & DEVALQUE, 2014, Collignoniceras woollgari regulare (HAAS, 1946), C. turoniense (SORNAY, 1951) and Collignoniceras vigennum AMEDRO & CHATELIER sp. nov. With regard to the top of the Tuffeau de Bourre Formation, it yielded about fifty specimens of ammonites but the assemblage is different to that found in the type locality of Bourre-Montrichard in the Cher valley. The material collected near the Vienne and Creuse junction includes : Lewesiceras peramplum (MANTELL, 1822), Romaniceras (Y.) ornatissimum (STOLICZKA, 1864), Collignoniceras woollgari regulare (HAAS, 1946), C. canthus (ORBIGNY, 1856) and C. turoniense (SORNAY, 1951). The species Collignoniceras papale (ORBIGNY, 1841), which represents one third of the Bourre collection is apparently absent whereas three new species belonging to the same genus are identified as : C. hourqueigi AMEDRO & CHATELIER sp. nov., C. badilleti AMEDRO & CHATELIER sp. nov. and Collignoniceras sp. A.