Tectonic and Karstic Morfphogenetic 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 between regional 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 Eurasian plates. The earlier phase, in the Messinan-Pliocene, caused crustal bulging and consequent uplift of the Hyblean region, followed by collapse of the marginal areas of the foredeep. During this period, active faulting, occurring in the northeastern sector of the Hyblean Plateau, led to the formation of NE-SW extensional basins (i.e. Lentini Graben) and a mature landscape developed 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-existing landscape, and the formation, along the Syracusan Ionian sector, of NW-SE oriented extensional basins (i.e. Anapo and Augusta Grabens) linked to the reactivation of tectonic lineaments along the seismogenetic system of the Hyblean-Maltese escarpment. With the start of uplift of the Hyblean Plateau, the surfaces exposed to meteoritic action show an initiation of karst formation. An intra-Messinian erosion surface thus developed at varying intensities, profoundly affecting the substratum consisting mainly of carbonates with minor intercalations of volcanics. Normal marine conditions were re-established during the Lower Pliocene only in marginal areas of the plateau, where the Trubi were deposited to “seal” the pre-existing paleomorphology 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 has continued to develop in exposed areas throughout the Pliocene and Quaternary. This has led to the generation of an epikarstic system with interconnected karstic conduits and galleries. These dissolution features indicate that their development has been controlled by both tectonic movements and Pleistocene global climatic variations, with eustatic regressive and transgressive events each leading to the development of a series of fossilised conduits within the aforementioned formations. During the Quaternary, the carbonatic outcrops of the eastern Ionian area were subjected to diffuse karst-forming processes dominated by both the tectonic activity, appearing at the Plio-Pleistocene passage and during the subsequent phases, and eustatic marine oscillations related to global climatic variations. Morphological evidence for such processes during the Pleistocene are recognizable along the structural depressions of the Anapo and Augusta grabens. In particular, regarding the structure of the Anapo, analysis of the elevations of fossile karstic phenomena present in the Miocene carbonate outcrops has led to the recognition of a cyclicity in the karst-forming processes, characterized by different velocities of deepening and senilisation, correlated with the elevations of marine terraces mapped along the Ionian sector.