The Subsurface Geology and Landscape Evolution of the Volturno Coastal Plain, Italy: Interplay between Tectonics and Sea-Level Changes during the Quaternary

The Volturno alluvial-coastal plain is a relevant feature of the Tyrrhenian side of Southern Italy. Its plan-view squared shape is due to Pliocene-Quaternary block-faulting of the western flank of the south-Apennines chain. On the basis of the stratigraphic analysis of almost 700 borehole logs and new geomorphological survey, an accurate paleoenvironmental reconstruction before and after the Campania Ignimbrite (CI; about 40 ky) eruption is here presented. Tectonics and eustatic forcing have been both taken into account to completely picture the evolution of the coastal plain during Late Quaternary times. The upper Pleistocene-Holocene infill of the Volturno plain has been here re-organized in a new stratigraphic framework, which includes seven depositional units. Structural analysis showed that two sets of faults displaced the CI, so accounting for recent tectonic activity. Yet Late Quaternary tectonics is rather mild, as evidenced by the decametric vertical separations operated by those faults. The average slip rate, which would represent the tectonic subsidence rate of the plain, is about 0.5 mm/year. A grid of cross sections shows the stratigraphic architecture which resulted from interactions among eustatic changes, tectonics and sedimentary input variations. On the basis of boreholes analysis, the trend of the CI roof was reconstructed. An asymmetrical shape of its ancient morphology - with a steeper slope toward the north-west border - and the lack of coincidence between the present course of the Volturno River and the main buried bedrock incision, are significant achievements of this study. Finally, the morpho-evolutionary path of the Volturno plain has been discussed.