Tectonic and Karstic Morphogenetic evolution of the northeastern sector of the Hyblean Plateau (Southeast Sicily)

In southeastern Sicily the Hyblean Plateau represents the foreland domain of the Neogene-Quaternary Apenninic-Maghrebian orogen. The morphotectonic evolution of the Hyblean Plateau is conditioned by the interaction betweenregional tectonic uplift and deformation induced by fault systems active during the different periods of morphogenesis.Such processes have found their expression during two distinct phases of the collision between the African and Eurasianplates.The earlier phase, in the Messinan-Pliocene, caused crustal bulging and consequent uplift of the Hyblean region, followedby collapse of the marginal areas of the foredeep. During this period, active faulting, occurring in the northeastern sector ofthe Hyblean Plateau, led to the formation of NE-SW extensional basins (i.e. Lentini Graben) and a mature landscapedeveloped as a result of a prolonged evolution under the control of a stable base-level.The later phase brought about the uplift of the entire Hyblean region, the dislocation and dissection of the pre-existinglandscape, and the formation, along the Syracusan Ionian sector, of NW-SE oriented extensional basins (i.e. Anapo andAugusta Grabens) linked to the reactivation of tectonic lineaments along the seismogenetic system of the Hyblean-Malteseescarpment.With the start of uplift of the Hyblean Plateau, the surfaces exposed to meteoritic action show an initiation of karstformation. An intra-Messinian erosion surface thus developed at varying intensities, profoundly affecting the substratumconsisting mainly of carbonates with minor intercalations of volcanics. Normal marine conditions were re-establishedduring the Lower Pliocene only in marginal areas of the plateau, where the Trubi were deposited to “seal” the pre-existingpaleomorphology and related deposits, postdating the Messinian karstic phenomenology.Karstic dissolution along the Monti Climiti and Monte Carrubba Formations was initiated in the Late Miocene and hascontinued to develop in exposed areas throughout the Pliocene and Quaternary. This has led to the generation of anepikarstic system with interconnected karstic conduits and galleries. These dissolution features indicate that theirdevelopment has been controlled by both tectonic movements and Pleistocene global climatic variations, with eustaticregressive and transgressive events each leading to the development of a series of fossilised conduits within theaforementioned formations.During the Quaternary, the carbonatic outcrops of the eastern Ionian area were subjected to diffuse karst-forming processesdominated by both the tectonic activity, appearing at the Plio-Pleistocene passage and during the subsequent phases, andeustatic marine oscillations related to global climatic variations.Morphological evidence for such processes during the Pleistocene are recognizable along the structural depressions of theAnapo and Augusta grabens. In particular, regarding the structure of the Anapo, analysis of the elevations of fossile karsticphenomena present in the Miocene carbonate outcrops has led to the recognition of a cyclicity in the karst-formingprocesses, characterized by different velocities of deepening and senilisation, correlated with the elevations of marineterraces mapped along the Ionian sector.