Influence of explosive volcanic events on the activation versus de-activation of a modern turbidite system: the example of the Dohrn canyon-fan in the continental slope of the Campania volcanic district (Naples Bay, Italy - Western Mediterranean)

Abstract:

The interplay between volcanic activity, volcano-clastic yield and activation/deactivation of a turbidite system can be evaluated along the continental margin of Campania region (Tyrrhenian Sea - Italy), an active volcanic area, where three wide canyon-fans occur at short distances ones to another. Actually, the Dohrn, Magnaghi and Cuma canyons cut the continental slope and shelf off Ischia and Procida volcanic islands and off the Campania Plain where Phlegraean Field and Mt. Vesuvius active vents are located.

This research is based on single-channel high-resolution seismic profiles (Sparker-One 16 kJ, 0.5 s twtt), swath-bathymetry and gravity cores litho- and tephra-stratigraphy. We focused on the stratigraphic position of paleo-thalweg features and channel/levees deposits in seismics, debris flow, turbidites and hemipelagites in cores, to learn more on the activation/deactivation stages of the canyon Dohrn, in the frame of relative eustatic sea level variations over the Middle Pleistocene-Holocene time span.

Preliminary outcomes suggest that even major volcanic events, such us ignimbrite eruptions or large fallout magnitude of between 80 to 1 km³ DRE, have caused the infilling of the canyon head, and the cover of pre-existing seabed morphology. As a consequence the temporary deactivation of the turbidite system occurred, despite the volcano-clastic overload in the coastal environment. Phases of renewed activities of the thalweg are observed to be in step with falling stages of sea level which have driven the re-incision of canyon valleys through continuous debris and turbidites down flows of volcano-clastic material. Presently, we observe the quiescence of the Dohrn Canyon despite the intense Holocene volcano-tectonic activity in the area.