The analysis of stratigraphic data from about 800 wells drilled in the Campanian Plain made possible to recognise a sequence of lithostratigraphic units among which two volcanic formations, Campanian Ignimbrite (33 kyr) and Neapolitan Yellow Tuff (12 kyr), have a great relevance owing to their areal distribution. The former spread out everywhere in the plain, the latter is distributed all around Campi Flegrei. Their thicknesses and their lithological features identify quite well these volcanic units in the stratigraphic sequences of wells. Wells data in the southern area of Alveo dei Camaldoli show the absence of Campanian Ignimbrite up to 200 m deep. In this area Neapolitan Yellow Tuff overlays some pyroclastic deposits younger than 21 kyr (Lirer et alii, 1991). A "yellow-reddish tuff" characterizes the stratigraphic sequence of the wells in the eastern area of Naples (Ponti Rossi, Capodichino, Casoria). It overlays Campanian Ignimbrite and is associated to an underlaying volcanic breccia deposit. The distribution of these deposits, along a NE-SO fracture system inferred by gravimetric analysis of the area, made possible to hypothesize a fissural eruption event. Moreover, between the eastern area of Naples and Somma-Vesuvio has been delineated a subsiding structural depression (Volla Depression) filled up with phlegraean and vesuvian volcaniclastic deposits inter-bedded with alluvial and lacustrine (peat) deposits. The study of wells data indicates that Volla Depression formed after Campanian Ignimbrite eruption.

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