Upper Triassic platform margin biofacies and the palaeogeography of Southern Apennines.

IN the Upper Triassic dolomitic successions of the Monti della Maddalena area (Southern Apennines) consist of white, heavily recrystallized and cataclastic dolomites evidences of bioconstructions can be found in several localities. These evidences are represented by rudstones and possibly boundstones whose main components are fragments of sponges (sphinctozoans, inozoans, chaetetids) and corals generally encrusted by foraminifera, red algae and ‘problematica’. This association is much more diversified with respect to that of the microbial-serpulid buildups which characterize the platform margin facies of most Upper Triassic successions of the Southern Apennines. The Monti della Maddalena biofacies can be more readily compared with the bioconstructed facies of Sicily and in general with the Dachstein-type reef of the Tethyan realm. The studied successions are interpreted (according to the model of Cirilli et al., 1999) as formed at the margin of a carbonate platform facing a deep basin having good connection with the open sea, while the microbial-serpulid buildups formed on the margin of intraplatform restricted troughs with poorly oxygenated bottom waters. Our study discusses the relative paleogeographic position of the Apennine platforms and the Lagonegro Basin. The overall picture of the bioconstructed Triassic facies distribution in Southern Apennines, together with biofacies data from resedimented facies of Lucania, are compatible with paleogeographic reconstructions interpreting the Monti della Maddalena successions as representing the more external sector of the Apennine platforms system flanking the Lagonegro Basin. The latter, bordered on its external side by Apulia, was part of a deep Mesozoic domain comprising the Imerese–Sicani basin of Sicily and connected westward with the East Mediterranean branch of Western Tethys. Our data exclude the possibility that the Lagonegro Basin was located in an internal position with respect to all the Apenninic and Apulian platforms system