Biostratigraphical study of the Middle-Upper Jurassic ammonite association of Stretta Arancio’s section (Southern Sicily, Italy).

This stratigraphical study is part of the revision work that has been carried out for the last ten years on some Jurassic successions outcropping in Southwestern Sicily. For this purpose, a synthesis of the data on the Middle-Upper Jurassic sequence from Stretta Arancio, near Sambuca di Sicilia (Agrigento Province) have been described in this paper. The deposits, constituting the succession of this area, are part of the Monte Magaggiaro-Pizzo Telegrafo Unit that belongs to a large tectonic unit located in the outer part of the Apennine-Maghrebide chain. During the Mesozoic Era, this Unit was part of the Saccense Domain, an area palaeogeographically located along the southern margin of Tethys. The studied succession consists of about 7 m of condensed pelagic limestones spanning from Middle to Upper Jurassic and covered by Upper Cretaceous limestones of the “Scaglia” type. The biostratigraphic study of Stretta Arancio has allowed us to identify the chronostratigraphic age and some biozones from Middle Jurassic (Middle Bathonian) to Upper Jurassic (Tithonian). Moreover, the taphonomic analysis of the recorded ammonite associations has given evidence of the presence of an important stratigraphic gap at the Bathonian-Oxfordian boundary, involving a registratic gap (i.e. a gap of the corresponding recording entity or Taxorrecord) of variable extent. Furthermore, this study has firstly allowed to assign the fossil assemblages to the Mediterranean Province and, secondly, to increase knowledge of the faunal associations of the area related to the pelagic carbonate platform system of Saccense Domain for the Middle-Upper Jurassic stratigraphic range.