GNGTS 2013 - Atti del 32° Convegno Nazionale

Unconformity Bounded Stratigraphic Units or UBSU) to synthesize the volcanic evolution of the area. The relative importance of a volcanic unconformity depends on its geographic extension, the duration of an associated hiatus, or its volcano-structural significance. The application of unconformity-bounded units to synthesize detailed lithostratigraphic units has been carried out in the south-western sector of the Phlegrean Fields volcanic complex (Perrotta et al. , 2010). The integration of field data by seismo-stratigraphic analysis of the Bay of Naples and wells drilled in the city of Naples (Milia, 2010) has allowed the reconstruction of the stratigraphic evolution of the southern margin of the Phlegrean Fields, highlighting the close relationships among volcanic activity, marine sedimentation and sea level fluctuations. This allowed to distinguish magmatic features, such as dykes, domes and tuff cones, deciphering the complex stratal architecture as an interplay between the syneruptive and intereruptive stratigraphic units. In this paper, a correlation with the onshore geology of the Phlegrean Fields has been carried out in order to highlight tectonic and magmatic implications in the geological evolution of the Phlegrean Fields volcanic complex, intensively studied through field geology (Rosi and Sbrana, 1987; Morhange et al. , 2005; Bellucci et al. , 2006; De Natale et al. , 2007; Bodnar et al. , 2007; Aiello et al. , 2013). Geologic setting. The Gulf of Pozzuoli, offshore the Phlegrean Fields volcanic complex (NaplesBay, southern Tyrrhenian sea) is an inlet with limited dimensions, bounded seawards by several submerged volcanic banks (Pentapalummo Bank; Nisida Bank; Miseno Bank; Fig. 1; Aiello et al. , 2012, 2013). The Phlegrean Fields is an active volcanic center near Naples, Italy (Fig. 2). Numerous eruptions occurred in this volcanic complex during the Late Quaternary (Fig. 2) and repeated episodes of slow vertical ground movement (bradyseism) have been documented since Roman times. Vertical ground movements have been observed since the nineteenth century, when the sea level marks left on the ruins of a Roman market called “Serapeo” in the Pozzuoli town indicated a strong volcano-tectonic subsidence of the area (Dvorak and Mastrolorenzo, 1991; Morhange et al. , 2005). The sea level measurements made within the Phlegrean Fields from 1819 to 1968 give an average subsidence rate of 14 mm/yr. Thermal cooling and contraction of a large magmatic body beneath this caldera have been Fig. 2 – Sketch morphological map of the Pozzuoli Bay (modified after Aiello et al., 2012). Key. 1: Wurmian regressive unconformity. 2: Depositional areas at the base of slopes. 3: Post-wurmian terraces. 4: Beach of Roman age. 5: Saddles buried between basins.. B: Intraplatform basins. 6: Morpho-structural slopes along regional faults. 7: Volcano-tectonic morpho-structural slopes. 8: Caldera rims. 9: Crateric rims. 10: Volcanic edifices. 11: Canyon’s heads and thalwegs. 12: Gas manifestations. 13: Physiographic margin of the inner shelf. 14: Physiographic margin of the central basin.. 6 GNGTS 2013 S essione 3.1