GNGTS 2016 - Atti del 35° Convegno Nazionale

536 GNGTS 2016 S essione 3.2 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 (Tab. 1). On the other side, a table of the seismic units of the southern Ischia offshore has also been constructed based on high resolution seismic data, focusing on the Ischia Bank, a wide and relict volcanic edifice located in the south-eastern Ischia offshore. A significant correlation may be desumed concealing the aspects on seismic stratigraphy of marine volcanic seismic units of Ischia and Pozzuoli, sectors, being important active volcanic areas of the Gulf of Naples during the Late Quaternary. Tab. 2 – Seismic units of the southern Ischia offshore (Ischia Bank). Seismic unit 1 V3-CI 3 V2-BI 5 FST/TST/HST 7 Dx Seismic facies Progradational geometries with eroded topsets and preserved clinoforms. Mounded-shaped, acoustically-transparent seismic unit. Discontinuous seismic reflectors having a high amplitude. Outer morphology of bank. Acoustically- transparent seismic facies. Discontinuous seismic reflectors having a high amplitude. Prograding clinoforms (FST) Retrogradational reflectors (TST) Parallel seismic reflectors (HST). Parallel seismic reflectors Parallel seismic reflectors Geological interpretation Relict prograding wedge (Late Pleistocene marine deposits) Volcanic unit of the Ischia Channel. Pyroclastites and lavas genetically related to the eastern Ischia offshore volcanic edifices (I Ruommoli, La Catena, Le Formiche di Vivara, il Pertuso). Pyroclastic unit in lateral contact with the V3-CI seismic unit. Volcanic unit of the Ischia Bank. Lavas and pyroclastic products genetically related to the monogenetic volcanic edifice of the Ischia Bank. Pyroclastic unit. Onlap on structural depressions and palaeo-channels. Marine counterpart of the Solchiaro Yellow Tuffs (18 ky B.P.; Procida island). Late Quaternary depositional sequence. FST: forced regression prograding wedges on the margins of the Ischia Bank. TST: transgressive fillings. HST: highstand deposits downlapping on flooding surfaces at the top of HST and TST. Pelites and sandy pelites cropping out at the sea bottom in outer shelf domains. Bioclastic deposits