Palaeontological study of Middle Oxfordian-Early Kimmeridgian (Late Jurassic) ammonites from the Rosso Ammonitico of Monte Inici (north-western Sicily, Italy)

This paper deals with the palaeontological study of ammonites collected in strata of Middle Oxfordian-Lower Kimmeridgian pro parte Rosso Ammonitico of two sections of Monte Inici (western Sicily, Italy), namely Monte Inici East and Castello Inici. The complete faunal list of ammonites collected in the Middle Oxfordian-Lower Kimmeridgian fossiliferous beds of Monte Inici succession is here presented for the first time. Thirty-two species have been described in the palaeontological study. As a result, the formerly published biozonation of the two successions exposed at Monte Inici has been refined. The biostratigraphical dating of the onset in the middle Oxfordian of both the radiolarite sedimentation at Castello Inici and the nodular facies of the Rosso Ammonitico at Monte Inici East is not coeval, as tentatively suggested in previous papers. On the basis of the vertical distribution of the species of the genus Gregoryceras Spath, 1924 the onset of cherty limestones in section Castello Inici slightly predates the onset of Rosso Ammonitico nodular facies observed in section Monte Inici East.Original Abstract: Etude paleontologique des ammonites du Rosso Ammonitico de l'Oxfordien moyen- Kimmeridgien inferieur (Jurassique superieur) de Monte Inici (Sicile nord-occidentale, Italie). Ce travail presente l'etude paleontologique d'ammonites du Rosso Ammonitico, de l'intervalle Oxfordien moyen-Kimmeridgien inferieur pro parte, dans deux localites du Monte Inici (Sicile occidentale, Italie, coupes de Monte Inici Est et Castello Inici). La liste faunique complete des ammonites recoltees dans les bancs fossiliferes de l'intervalle Oxfordien moyen-Kimmeridgien inferieur de Monte Inici est presentee pour la premiere fois. Trente-deux especes ont fait l'objet d'une description paleontologique qui a permis d'affiner la biozonation des successions exposees dans les deux coupes du Monte Inici, presentees dans des publications precedentes. Sur la base de la distribution verticale des especes du genre Gregoryceras Spath, 1924 il est possible de refuter le synchronisme de la mise en place, a l'Oxfordien moyen, de la sedimentation radiolaritique a Castello Inici et du facies noduleux du Rosso Ammonitico a Monte Inici Est; le premier evenement est legerement plus ancien.