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A main volcanic marker has been identified for the first time on the continental shelf of the northern Phlegraean Fields in the Gaeta Gulf (Campania region, eastern Tyrrhenian margin, Italy) by means of Subbottom Chirp profile grid and stratigraphic analysis of a core collected on the slope. In the seismic sections, the core bottom corresponds to the top of a continuous and parallel reflector (V) interbedded within the transgressive deposits of the Late Quaternary-Holocene depositional sequence. The Transgressive System Tract deposits are particularly thick compared to the majority of the transgressive deposits of other shelf settings. This might be due to the input of pyroclastic and volcanoclastic deposits related to the intense eruptive activity of the Campania Plain during the Late Pleistocene-Holocene time span. Undulations and pockmarks are the main morphological features of the sea floor and they might be linked to gas uprising, widely detected in the study area. The V reflector is located on the shelf from northeast to southwest at different depths, ranging from 10 ms (about 8 m) to 30 ms (about 25 m) below sea floor and it can be mapped down to the continental slope. The geological calibration of this continuous reflector coupled with tephrostratigraphic analysis, allowed to correlate it with the Neapolitan Yellow Tuff deposits emplaced at Phlegraean Fields at ca. 15 ka.

The interactions between Late Quaternary volcanic and sedimentary processes in the Naples Bay, Southern Tyrrhenian sea are here discussed through the results of the marine geological survey at the 1:10.000 scale. The example of the geological map n. 465 "Isola di Procida", herein presented, has put in evidence the stratigraphy of marine Quaternary deposits and related volcanic seismic units. The volcanic deposits cropping out in the Procida island have been explained as the result of eruptions coming from local eruptive centres. The geological survey carried out onshore indicate the occurrence of several pyroclastic units linked to the eruptive activity of the Ischian and Phlegrean volcanic complexes, interstratified with the products erupted by local centres. The occurrence in the pyroclastic sequences of Ischia and Procida islands of several marker horizons and their stratigraphic correlations have allowed to reconstruct the volcanological evolution of the two islands and the interactions with sedimentary processes at the scale of the whole Tyrrhenian margin. Fifteen geological maps at the scale 1:10.000 covering the whole Naples Bay have been constructed based on the interpretation of marine geological and geophysical data. The stratigraphic relationships between the lithostratigraphic units and the eruptive deposits have testified the activity of several volcanic monogenic centers, whose products are interstratified with marine and continental deposits of the Late Quaternary depositional sequence.