Marine stratigraphy of active volcanic areas in the Campania offshore: correlation between the seismic units of the Gulf of Pozzuoli and Ischia island

INTRODUCTION The marine stratigraphy of active volcanic areas located in the Campania offshore is herein shown and discussed based on high resolution seismic data (Sparker seismic source). Selected examples located in the Gulf of Pozzuoli and in the Ischia offshore will be shown. New and innovative geological and hazard maps of volcanic terrains have been presented, dealing with the definition of mapped units during the field survey, highlighting that a geological map represents a warehouse in which to store the data existing on past eruptions and on inter-eruptive phenomena, having significant implications on the volcanic hazard assessment (Lucchi et al., 2010; Tibaldi, 2010; Bonomo and Ricci, 2010; Palladino et al., 2010; Viereck-Goette et al., 2010; Martì et al., 2010; Gertisser et al., 2010; Milia, 2010; Perrotta et al., 2010; De Vita et al., 2010; De Beni and Groppelli, 2010; Cortes et al., 2010; Vargas-Franco et al., 2010; Sheridan et al., 2010). Marine stratigraphy of active volcanic areas in the Campania offshore has been previously discussed, focusing on examples located in the Gulf of Pozzuoli and Ischia island (Aiello et al., 2012a; 2012b). The techniques of sequence stratigraphy have been successfully applied in seismo-stratigraphic interpretation of high resolution seismic data to produce reliable geoseismic sections showing the stratigraphic relationships among volcanic bodies and interstratified marine deposits, mostly pertaining to the Late Quaternary depositional sequence (De Lange et al., 1989; Amorosi et al., 2008; Riboulot et al., 2012; Oyedele and Duprè, 2014; Aiello and Marsella, 2015). The contribution of alluvial and marine sediments has controlled marine patterns and depositional sequences. The thickness of Pleistocene-Holocene marine sediments in the Ischia offshore ranges between 425 m and 170 m based on computed seismic lines, being higher in western Ischia offshore. Sedimentary drapes have been detected along all the southern continental slope of the island, reaching a thickess of several tens of meters. GEOLOGIC SETTING The Gulf of Pozzuoli represents the submarine prolongation of the Phlegrean Fields, a volcanic district surrounding the western part of the Gulf of Naples, which was active during the last 50 kyr (Rosi and Sbrana, 1987). It is located in a central position within the graben of the Campania Plain. Pre-calderic and post-calderic volcanic activity have been distinguished. The first one developed in correspondence with small and scattered volcanic centers, erupting trachytic pyroclastites and lavas. The second one was characterized by four main phases and has been constrained through deep geothermal drilling in the Phlegrean area. Being located westwards to the Phlegrean caldera, the Ischia island is formed by volcanic rocks erupted from different centers, ranging in age from 150 ky B.P. and 1302 A.D. The geologic setting is dominated by the Monte Epomeo structure (787 a.s.l.), whose formation was controlled by the volcano-tectonic uplift consequent to the caldera resurgence triggered by the eruption of the Epomeo Green Tuffs, happened at 55 ky B.P. (Vezzoli, 1988). The Southern Ischia canyon system has been investigated in detail (Aiello and Marsella, 2014), showing significant erosional processes in correspondence of canyons individuated off Barano and Maronti, active during recent times. RESULTS A sketch table of marine seismic units in the Gulf of Pozzuoli has been constructed based on the interpretation of high resolution seismic data (Table 1). Seismic unitSeismic faciesGeologic interpretationLocation HSTProgradational to parallel seismic reflectorsHighstand System Tract (HST)Eastern sector of the Gulf of Pozzuoli TSTRetrogradational seismic reflectorsTransgressive System Tra