The Neapolitan Yellow Tuff tephra in the stratigraphic architecture of the Gulf of Gaeta shelf, eastern Tyrrhenian margin

The Neapolitan Yellow Tuff (NYT) caldera-forming eruption (ca. 15 ka; Deino et al., 2004) is a large event occurred at Phlegraean Fields during the late Pleistocene-Holocene. It produced a widespread isochron marker which links marine and terrestrial archives of the central Mediterranean area and northern Europe. In this research we describe the stratigraphic signature of the NYT deposits in the Late Pleistocene-Holocene shelf sequence of the Gulf of Gaeta (northern Campania region, southern Tyrrhenian sea) by using a number of gravity cores along with a grid of seismic lines that include Subbottom Chirp, Sparker 1kJ and Uniboom profiles. The Gulf of Gaeta represents the northern Campania continental margin that is part of a large extensional Plio-Pleistocene basin associated with normal and strike-slip faults linked to the evolution of the eastern Tyrrhenian Sea margin. Since mid-late Pleistocene, extensional tectonics took place across the continental margin and it was accompanied by intense volcanism, from several districts of which the Phlegraean Fields activity has greatly influenced the sedimentation in this sector. The continental shelf, gently sloping seaward, is as wide as 30 km in front of the Garigliano river and narrows southward reaching its minimum width of ca. 10 km seaward of Cuma; the shelf break is located between 120 m and 125 m depth. The upper Pleistocene-Holocene stratigraphic architecture of the continental shelf is characterized by an offlap prograding succession followed by a very thick transgressive onlapping unit and by the upper highstand unit mainly characterized in the southern sector by undulations probably linked to gas prone sediment. The slope is characterized by a uniform profile and, in the southern sector, it is incised by several submarine gullies. According to Chiocci and Casalbore (2011), the high thickness of sediment on the shelf and slope area was influenced by hyperpycnal flows, linked to the sudden and large supply of pyroclastic and volcaniclastic deposits in the Volturno river catchment basin. In the studied seismic sections, the NYT matches a highly continuous and parallel reflector which is interbedded within the transgressive systems tract deposits. The deposit was recovered in cores raised from the slope, where it is present few milliseconds below the sea floor, while on the shelf where it is located at higher depths, ranging from 10 to 30 ms (8 to about 25 m) below sea floor, has been mapped out through the seismic lines.. The tephrostratigraphic analysis allowed to characterize the NYT in terms of lithology and chemistry and to provide new insights into the depositional mechanisms in the marine environment.