Geomorphological evidences of the eustatic control on the Quaternary evolution of Balai coastal karst area (North Sardinia, Italy)

The carbonate outcrop of Porto Torres constitutes the unique coastal karst of North Sardinia. In this study its geomorphological features have been investigated focusing along the Balai headland with the aim to reconstruct the eustatic and/or tectonic history of this coast. In the area various orders of active and fossil wave-cut shore platforms, marine terraces, fossil and modern tidal notches, and lithodome holes bands have been observed at different elevation along the 3 km long carbonate shoreline. Other coastal physiognomies are directly related to karst dissolution and comprise coastal karren fields, solution pans and several caves opening along the marine cliff. Among the karst systems, Fungo Cave is one of the most interesting. It is composed of two overlapping cave levels clearly developed along weakness in the limestone host rock. The marine influence on speleogenesis and its correlation with the current sea level have been analysed. In fact, it seems that cave development reflects the change in the eustatic conditions: the upper conduits formed likely during last interglacial, while the lower passages developed during sea level fall. Also a slight tectonic uplift is not excluded. Both eustatic and tectonic processes are also responsible for the whole evolution of the typical landscape in the coastal karst of Balai promontory.