The Campi Flegrei area is structurally dominated by the caldera associated with the eruption of theNeapolitan Yellow Tuff (NYT), a 40 km3 DRE ignimbrite dated at ca 15 ka BP [Deino et al., 2004], Thevolcanological evolution of the NYT caldera as been long described on the basis of outcrop and subsurfacestudies onland [Rosi & Sbrana, 1987; Orsi et al., 1996, and references therein; Di Vito et al., 1999; Perrotta etal., 2006; Fedele et al., 2011], but its offshore morphology, the stratal geometry of the volcaniclastic productsand structures and the late-stage geodynamic evolution of the inner caldera resurgence are still poorly known.We integrate geological and geophysical data obtained from high-resolution reflection seismic profiles(Sparker and Chirp sources) with gravity cores and swath bathymetry to better constrain the shallow structureand stratigraphic architecture and latest Quaternary to Holocene evolution of the submerged sector of the NYTcaldera off the Pozzuoli Bay.Our data clearly image, for the first time, the offshore geometry of the NYT caldera ring-fault zone, aswell as the volcano-tectono-sedimentary evolution associated with the late stage evolution of the NYT innercaldera resurgence. Our interpretation suggests that since 15 ka the offshore sector of NYT inner calderaunderwent significant deformation and uplift (with minor subsidence episodes) that occurred almost at the samerate as the post-glacial sea-level rise. Particularly, the inner Pozzuoli Bay started to deform soon after 15 ka BP,when the sea-level rise was initially faster than uplift. This caused a general increase of the accommodationspace that was progressively filled up by volcaniclastic sediments. Since ca. 8 ka BP, along with the midHolocene decrease in the rate of the sea-level rise, the early NYT resurgent structure was then uplifted up to thesea-level or even to partial subaerial exposure. From ca. 8 to 5 ka BP two distinct layers of resediments, mostlyrepresented by density current deposits, separated by an interval of hemipelagic sediments. The two densityflow units display a remarkable difference in their thickness and internal geometry. Across the bay, the lowerunit is ca 5m thick in the western sector and reaches its maximum of ca 10 m in the central sector while it isabsent towards the east. The upper unit, on the contrary, displays the minimum thickness of 10 m close to thecentral sector of the bay and increases up to ca 16 and 12 m in the western and eastern sector of the bay,respectively. The variation in thickness of the density flow deposits appears to be related with the amount ofsediments available. The upper density flow deposits is also internally more chaotic respect to the lower one,suggesting higher energy and/or turbulenceA significant post 2 ka BP subsidence phase of ca 10 m is then recorded offshore Pozzuoli by thedrowning of the infralittoral prograding wedge below the present-day fair-weather wave base. Sections clearlyillustrate that the basin depocentre topography is not fixed at one position but migrates southwards in time.We suggest that the uplift of the resurgent dome and subsidence of the southern sector, occurred after theeruption of the NYT, acted as a major control in the increase of the sea-floor gradient in the Pozzuoli bay. Thismay have triggered in turn, the deposition of gravity flow deposits along with a progressive migration of basindepocentres through time.
|Numero di pagine||2|
|Stato di pubblicazione||Published - 2012|