The influence of paleogeographic setting and crustal subsidence on the architecture of ignimbrites in the Bay of Naples (Italy)

The Margin of Campania (including Campania Plain and the Bay of Naples) featured recurrent large-scale ignimbrite eruptions between 270 and 15 ka. These ignimbrite deposits are exposed in the valleys of the Apennines and in limited areas along the Margin of Campania, whereas are covered by younger deposits in the Campania Plain and the Bay of Naples. Of all these eruptions, the Campania Ignimbrite (39 ka) and the Neapolitan Yellow Tuff (15 ka) are the best studied and are considered to be the most important. Numerous papers suggest that these two eruptions originated from one or two nested calderas located in Campi Flegrei and the Bay of Pozzuoli, in the northern part of the Bay of Naples. The recognition of the way, the site and the timing of a volcano-tectonic collapse is of paramount importance to establish which of the structures were active during the eruption. Our study demonstrates that the recognition of the areas involved in volcano-tectonic collapses is possible by means of a three-dimensional basin analysis. In the Bay of Naples the sequence stratigraphy interpretation of more than 4000 km of single-channel and multi-channel seismic reflection profiles made it possible to reconstruct the three-dimensional architecture of the ignimbrite units. Basin analysis reveals that before ignimbrite eruptions the physiography of the Bay of Naples was characterised by a lateral variation in depositional environment ranging from shelf to deep marine. Our structural and stratigraphic analysis documents volcano-tectonic deformations that occurred during the eruptions of the Pre-Campania Ignimbrite tuffs and of the Campania Ignimbrite: these deformations were controlled by normal faults with planar geometry. The overall features of the Campania Ignimbrites and the quantitative evaluation of crustal subsidence support a model of fissural emission associated to an asymmetrical crustal subsidence of the Campania Margin.