GNGTS 2016 Sessione 3.2

Marine stratigraphy of active volcanic areas in the Campania offshore: correlation between the seismic units of the Gulf of and island G. Aiello CNR-IAMC Sede di Napoli, , Italy

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

534 GNGTS 2016 Sessione 3.2 been successfully applied in seismo-stratigraphic interpretation of high resolution seismic data (Fig. 1) 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). Tab. 1 – Table of the seismic units in the Gulf of Pozzuoli (high resolution seismic stratigraphy).

Seismic unit Seismic facies Geologic interpretation Location HST Progradational to parallel Highstand System Tract (HST) Eastern sector of the Gulf of seismic reflectors Pozzuoli TST Retrogradational seismic Transgressive System Tract (TST) Eastern sector of the Gulf of reflectors Pozzuoli Lsl Wedge-shaped chaotic and Landslide deposits interstratified Gulf of Pozzuoli, south of discontinuous seismic unit. in the upper part of LST; Miseno Cape. occurrence of palaeochannels. LST Progradational seismic reflectors, Lowstand System Tract (LST) Inner continental shelf of the erosionally truncated at their Gulf of Pozzuoli top. G1 Parallel and continuous seismic Upper unit of the Pozzuoli basin Gulf of Pozzuoli reflectors. fill. Lsl2 Wedge-shaped chaotic and Fossil submarine landslide Eastern sector of the Gulf of discontinuous seismic unit overlying the G2 marine unit Pozzuoli and underlying LST deposits. NYT/PC NYT: wedge-shaped acoustically NYT: pyroclastic deposits of the Naples and Pozzuoli transparent volcanic seismic unit. Neapolitan Yellow Tuff (12 ky), offshore. PC: mound-shaped acoustically- deposited in Naples and Pozzuoli transparent volcanic bodies offshore. interstratified with parallel PC: Tuff cones of the Nisida reflectors. volcanic complex, in facies hetheropy with NYT and interstratified with G3 marine deposits. G2 Parallel and continuous seismic Intermediate seismic unit of the Gulf of Pozzuoli. reflectors. basin fill; marine clastic deposits involved by strong wedging and growth, showing the activity of synsedimentary tectonics. Lsl1 Wedge-shaped, chaotic to Wide paleo-landslide Eastern sector of the Gulf of discontinuous seismic unit. overlying the V3 volcaniclastic Pozzuoli unit and coeval with the basal part of the G2 marine unit. Pyr2 Continuous progradational to Pyroclastic unit Offshore from Capo Miseno to parallel seismic reflectors Miseno Bank dK Sub-vertical volcanic bodies, Volcanic dykes due to magma Eastern and central Gulf of acoustically-transparent and uprising in correspondence to Pozzuoli. locally bounded by normal faults. normal faults. Pyr1 Discontinuous to parallel seismic Pyroclastic unit Structural depression under the reflectors. volcanic edifice of Capo Miseno G3 Discontinuous to parallel seismic Lower sedimentary unit of the Naples and Pozzuoli Gulfs. reflectors. basin fill deformed in anticlines (Punta Pennata anticline, Pozzuoli anticline, Nisida anticline) and corresponding synclines (central syncline of Pozzuoli; Epitaffio syncline). V3 Discontinuous and acoustically- Volcaniclastic unit related Gulf of Pozzuoli. transparent seismic unit, strongly to the northern margin of eroded at its top. the Pentapalummo bank, deformed by aforementioned compressional structures.

535 GNGTS 2016 Sessione 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 , 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 Seismic facies Geological interpretation 1 Progradational geometries with eroded topsets Relict prograding wedge (Late Pleistocene marine and preserved clinoforms. deposits) V3-CI Mounded-shaped, acoustically-transparent seismic Volcanic unit of the Ischia Channel. Pyroclastites unit. and lavas genetically related to the eastern Ischia offshore volcanic edifices (I Ruommoli, La Catena, Le Formiche di Vivara, il Pertuso). 3 Discontinuous seismic reflectors having a high Pyroclastic unit in lateral contact with the V3-CI amplitude. seismic unit. V2-BI Outer morphology of bank. Acoustically- Volcanic unit of the Ischia Bank. Lavas and transparent seismic facies. pyroclastic products genetically related to the monogenetic volcanic edifice of the Ischia Bank. 5 Discontinuous seismic reflectors having a high Pyroclastic unit. Onlap on structural depressions amplitude. and palaeo-channels. Marine counterpart of the Solchiaro Yellow Tuffs (18 ky B.P.; Procida island). FST/TST/HST Prograding clinoforms (FST) Late Quaternary depositional sequence. Retrogradational reflectors (TST) FST: forced regression prograding wedges on the Parallel seismic reflectors (HST). margins of the Ischia Bank. TST: transgressive fillings. HST: highstand deposits downlapping on flooding surfaces at the top of HST and TST. 7 Parallel seismic reflectors Pelites and sandy pelites cropping out at the sea bottom in outer shelf domains. Dx Parallel seismic reflectors Bioclastic deposits

536 GNGTS 2016 Sessione 3.2

Fig. 1 – Location map of the seismic profiles.

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