Progressive changes in rifting directions in the Campania margin (Italy): New constrains for the Tyrrhenian Sea opening

Current models for the opening of the Tyrrhenian Sea invoke a unique extension vector throughout the rift to drift process, accommodated by margin parallel faults, but the role of the Campania margin faults in the opening of the Tyrrhenian back-arc basin is still poorly constrained. Gaeta Bay, located on the Campania margin, was investigated through the interpretation of seismic reflection and borehole data together with a stratigraphic correlation of dated outcropping units. The interpretation of a seismic grid using seismic and sequence stratigraphy and structural geology approaches in a dedicated GIS environment led to the generation of 2-D models of relevant geological surfaces, isochron maps, a 3-D digital model of the subsurface and to the reconstruction of the geological evolution of the margin with a resolution of 100 ka. Gaeta Bay is formed by three basins (northern, central and southern) and features a complex stratigraphic architecture: in the northern and central basins a syn-rift deposit (unit PP) is buried by the oldest aggradational deposit (unit A) that fills the accommodation space; a post 0.7 Ma succession (units B and C) filled the northern basin with a lateral aggradational geometry; a syn-tectonic wedge (unit B) was deposited in the central basin between 0.7 and 0.4 Ma; post 0.4 Ma thick deposits (unit C) are testimony to the collapse of the southern basin. A correlation between the geology of the bathyal basin and that of the Campania margin was established using a CROP seismic section that extended from the Vavilov basin to Gaeta Bay. Based on original and literature data we propose a kinematic evolution of the Tyrrhenian Sea upper plate over the last 10 Ma. This evolution consists of older extensional events (stages 1–2) off Sardinia and in the Vavilov basin (leaving the Campania margin unaffected). Younger events (stages 3–5) developed in the eastern (with a Pliocene–Quaternary change of the extension direction along the Campania Margin) and central Tyrrhenian region. This paper suggests that the Tyrrhenian Sea opening was a polyphase rifting with a migration of activity and a change of style over time (including a period of lithospheric detachment faulting).