Tectonic-stratigraphic evolution of the Longobucco Basin (NE Calabria), from Jurassic extension to Cenozoic compression: the Paludi Fm

The Longobucco Basin is part of the Calabria-Peloritani Terrane (CPT hereafter). The CPT is an exotic crustal fragment which, along with the Lesser and Greater Kabylias, Rifian-Betic and Alboran terranes, drifted from its original paleogeographic position and was accreted to the Apennine-Maghrebian chain. The Mesozoic paleogeographic affinity of these crustal fragments is still debated as they are considered as i) part of the southern European margin, ii) part of an independent microplate named AlCaPeKa (although the original meaning given by Boullin, 1986, was altered by subsequent authors) or Mesomediterranean Microplate (Guerrera et alii, 1993), and iii) part of the African margin. Reconstructing the geodynamic evolution of these crustal fragments has proved to be a tricky task because these elements were originally located at the boundary between the African and European plates, where the Alps, Apennines, Pyrenees and Betics developed. This boundary was the site of interaction between two opposite subduction systems, whose mode and timing of interplay is still debated in the literature (see Malusà et alii, 2018 for a review). The Cenozoic geodynamic puzzle at this plate boundary was further complicated by the opening of backarc basins, causing the fragmentation and drifting of AlCaPeKa from its original paleogeographic position. During their drifting, these allochthonous elements collided with the African plate, becoming part of the Apennine-Maghrebide accretionary wedge. This caused the coexistence and juxtaposition, in the innermost portion of the Chain, of radically different successions, with contrasting paleogeographic affinities (i.e., European vs African), and a distinct tectonic/stratigraphic evolution with respect to the backbone of the Apennines. Northern Calabria can be taken as an example of such a complex scenario, as the Costal Chain (Western Calabria) is indeed a part of the Alpine orogen, which drifted and was eventually accreted to the Apennines (Rossetti et alii, 2001). The timing of tectonic and stratigraphic events related to the Cenozoic evolution of the Arc are well constrained in its southern portion (i.e., the Peloritani Mts., north-eastern Sicily), following an in-depth study of the upper Eocene-lower Oligocene synorogenic siliciclastic deposits of the Frazzanò Fm., the upper Oligocene-Aquitanian Capo d’Orlando Fm. (Catalano et alii, 1996), the post-orogenic Burdigalian deposits of the Calcareniti di Floresta Fm. (Lentini & Carbone, 2014), and the completion of the official geological maps of the area (e.g., Catalano, 2009; Servizio Geologico d’Italia, 2009). The Sicilian authors (Lentini & Carbone, 2014) have highlighted the existence of an older tectonic phase (with respect to the canonical late Miocene thrusting phase of the Central Apennines), named “Balearic phase” (Lentini & Carbone, 2014), corresponding to the stacking of the Calabride Units, and their emplacement on top of the Liguride Complex. 2 In Northern Calabria, the tectonic evolution of the Coastal Chain (Liguride Complex), and of the so-called Northern Calabrese Units pertaining to the Panormide Complex, have been thoroughly investigated (see Vitale et alii, 2019). In contrast, the Cenozoic deposits of the Calabride Complex are only found in the Longobucco Basin and are underinvestigated (but see section on previous studies), which led in our view to an unsatisfactory interpretation of the evolution of the Arc by modern standards. As demonstrated by the studies of the Sicilian Authors, an in-depth analysis of siliciclastic units, and consequent identification of pre-, syn-, and late-orogenic deposits, is crucial to the understanding of the geodynamic evolution of such troubled areas. A geological mapping project in the Longobucco Basin proved essential for elucidating the tectonic-sedimentary evolution of northern Calabria, from Jurassic extension to orogenic compression. This paper will focus on the Cenozoic Paludi Fm, a poorly known multifaceted, unconformity-bounded siliciclastic unit, generically interpreted in the literature as an “Apennine flysch” (Magri et alii, 1965; Zuffa & De Rosa, 1978; Bonardi et alii, 2005). By understanding the geological significance of the Paludi Fm a re-interpretation of the paleogeographic affinity of the Calabride Complex will be provided, shedding also light on the primordial phases of the Apenninic evolution