Palaeogeographic, palaeoclimatic and palaeoenvironmental variations of the Jurassic successions of the south-western Tethys

Studying ancient oceans is fundamental for reconstructing Earth’s geological history and for understanding the long-term interactions between tectonics, climate, and life. From a palaeogeographic perspective, the analysis of past oceans allows to reconstruct the continental configurations, seaways, and oceanic gateways, which have a primary control on ocean circulation patterns. In palaeoenvironmental terms, ancient marine successions preserve key evidence of variations in water depth, oxygenation, productivity, and sedimentary regimes, providing insights into the dynamics of marine ecosystems through time. From a palaeoclimatic viewpoint, past oceans played a central role in regulating heat distribution, carbon cycling, and atmospheric composition, as in the present-day oceans. In this context, the Tethys Ocean represents a key archive of Mesozoic palaeoceanographic and palaeoclimatic evolution, as its complex evolution strongly influenced global circulation, climate gradients, and biotic exchanges between the northern and southern hemispheres. This significance is further enhanced by the widespread and well-preserved Tethyan sedimentary successions exposed across Europe and North Africa whose abundance and accessibility make the region particularly suitable for detailed palaeogeographic, palaeoenvironmental, and palaeoclimatic studies. Consequently, the Tethys has been the focus of numerous multidisciplinary investigations, which have established a robust stratigraphic, sedimentological, and geochemical framework, enabling regional datasets to be integrated into a coherent model of Mesozoic oceanic and climatic evolution (e.g, Ziegler, 1998; Guerrera et al., 2005; Dera et al., 2011; Puga et al., 2011; Kairouani et al., 2024 and references therein).During the Mesozoic, the Western Tethys was characterized by a wide carbonate platform facing large deep-water areas to the north and east (Wendt, 1969; Jenkyns, 1970; Catalano et al., 1996, 2000), growing on the stretched African continental crust (Catalano et al., 2013b). During the Rhaetian and the early Jurassic, the carbonate platforms were dissected due to extensive tectonics related to the continental rifting that involved the Pangea supercontinent (Catalano and D'Argenio, 1982; Dewey et al., 1989). Therefore, the shallow water carbonate sedimentation continued on large faulted blocks since the late Hettangian/early Sinemurian times (Gugenberger, 1936; Arkell, 1957; Giacometti and Ronchi, 2000). By the middle/late Sinemurian the carbonate platforms undergo a drowning phase turning into pelagic carbonate platform (sensu Santantonio, 1993) on which took place the deposition of condensed pelagic sediments informally indicated as “Rosso Ammonitico” (Catalano et al., 1981; Di Stefano, 2002a).The Rosso Ammonitico is one of the most representative Mesozoic condensed deposits of the Western Tethys. Traditionally defined as a thin, nodular to massive red limestone enriched in ammonites and radiolarian-bearing wackestones–packstones, it records long-term intervals of reduced sedimentation, seafloor condensation, and early diagenetic lithification along the Jurassic passive margins of the Tethys Ocean. These condensed deposits are usually associated with Fe-Mn crusts and nodules, which occur as discontinuous coatings, encrustations or discrete concretions on hardgrounds and firmgrounds, reflecting prolonged extremely low sedimentation rate (Di Stefano and Mindszenty, 2000).The widespread occurrence of those condensed deposits along large sectors of the African continental margin, from Sicily to the Subbetic, Dinarides and the Aegean region, makes it a key element for interregional stratigraphic correlation. Moreover, the presence of hardground and Fe-Mn crusts, at the base and within the condensed pelagic deposits, represents a global signal of palaeoceanographic and palaeoenvironmental changes.This PhD thesis aims to advance understanding how tectonics, climate and environmental conditions affect sedimentation in areas characterized by continental rifting processes. The main objective is to provide insights, through a multidisciplinary approach that integrates stratigraphic and biostratigraphic (benthic foraminifera and ammonite biostratigraphy) data, microfacies and compositional analysis, to observe the interactions between climate, sedimentation and tectonics. Emphasis is placed on the role the Fe-Mn crusts and nodules and of the Ammonitico Rosso condensed deposits as a key archive of Mesozoic palaeoenvironmental and palaeoclimatic change, and its importance in reconstructing the palaeogeographic evolution of the Mediterranean region. The study was carried out analysing several stratigraphic successions that span across the above mentioned interval and that outcrop in western and southwestern Sicily. Moreover, one additional section, outcropping in southern Spain, was studied in order to make correlation with Sicilian sections. Three sections are described in detail (see paragraph 1.2) while the other data collected are presented in the last chapter of the thesis as supplementary material (see Chapter 5).