Middle and Upper Jurassic record in the Western Sicily successions

Middle-Upper Jurassic successions cropping out in western Sicily have been the subject of detailed sedimentological, stratigraphic and palaeontological studies over the last 15 years based on the analysis of ammonite associations. Studies are preferentially focused on the Bathonian-Tithonian chronostratigraphic interval. Some studied successions represent the type-locality of many ammonite species defined by G.G. Gemmellaro, while others have been known only in Sicilian geological literature.The examined sequences were sedimented in different depositional environments (moderately deep external carbonate platform) called Domains, more precisely, the Trapanese and Saccense Domains (TP, Trapanese Domain and SD, Saccense Domain), which during the Middle-Upper Jurassic were located in the western sector of the Tethys. The Sicilian studied sequences may be regarded as highly condensed, Ammonitico Rosso facies, developed on epioceanic environments similarly as Betic Chains (Sequeiros, 1974), Transdanubian Central Range in Hungary (Fözy & Meléndez, 1996; Fözy et al., 1997) and Western Greece.The compared study of Callovian-early Tithonian ammonite successions in pelagic carbonate sequences across West Sicily show clear palaeobiogeographical differences not only between the Trapanese and Saccense domains, but also within the latter.All the successions of the TD (Rocce del Calderaro, Sant’Anna and Erice Ter at Mt. Erice) and the SD (C.da Diesi, Cava ex-Capraria, Stretta Arancio and Vallone San Vincenzo) show a Mediterranean-type fauna. It includes common representatives of suborder Phylloceratina and, among Ammonitina, the bulk of recorded associations is formed by representatives of Mediterranean subfamilies such as Passendorferiinae, Euaspidoceratinae and Peltoceratinae with a minor representation of family Oppeliidae. The ammonite recorded associations from the C.da Diesi succession, belonging to the Saccense Domain, show a typical assemblage, ranging from lower to early middle Oxfordian (Antecedens Sub-Biozone, Plicatilis Biozone), composed by a reduced number of specimens but showing a clear predominance of representatives of subfamily Perisphinctinae over Passendorferiinae. Especially noteworthy are representatives of genus Platysphinctes and, in the last association of this assemblage, of Tornquistes spp. The low share of representatives of the typical tethyan group Phylloceratina marks a clear difference with similar associations from other near areas belonging to the Trapanese Realm where these typical tethyan groups are dominant. The upper assemblages instead show a typical mediterranean fauna, even if there are some dubious specimens of Perisphinctinae and, for the first time in the Sicilian faunas, a representative of genus Clambites has been found.In all the studied sections the Middle Jurassic, recorded from the Upper Bajocian (Contrada Monzealese) throughout the Callovian (Vallone San Vincenzo), is characterized by the same Bositra limestone facies and reaches its maximum thickness at Vallone San Vincenzo and Cava ex-Capraria sections, whilst in the sections of Contrada Diesi and Stretta Arancio, instead, the sequences show a remarkeble reduction in thickness.The Callovian-Oxfordian transition in Sicily was marked by a wide stratigraphic gap ranging presumably from Upper Callovian to Middle Oxfordian (upper Plicatilis Zone, Antecedens Subzone). However, this gap is not homogeneous and sometimes is more expanded and involves the entire Callovian (Stretta Arancio section) (Cusumano et al., 2013).The Oxfordian, represented always by