Complex stratigraphic relationships between volcanic features and sedimentary deposits in a submarine environment: The northern offshore Holocene Ischia volcanic field (Italy)

The correlation between onshore and offshore of the volcanic features in a complex volcanic field area is a difficult task, however, it is a fundamental step in order to better understand the geological evolution of such a complex area and for an assessment of geologic hazards. Ischia is a well exposed and densely populated volcanic field located in the Campania volcanic province of Italy. In order to improve our understanding of the recent volcanic history of Ischia Island, high-resolution seismic reflection profiles were used to identify volcanic and sedimentary features in the northern offshore. The volcano stratigraphy interpretation permitted us to recognize seismic units with a reflection-free/chaotic facies. These latter units have been associated with volcanic deposits and correlated to the main volcanic units outcropping on the northern coast of Ischia Island. They are limited in extent and interlayered with eight seismic units with continuous reflectors corresponding to clastic sedimentary units that were deposited during intereruptive phases. The main result of this work is the documentation of volcanic activity during the Holocene in the area offshore between Castello d'Ischia, Ischia Porto (mainly effusive products) and Punta della Scrofa (mainly shallow lava domes and dykes). The key volcanic units were mapped and 3D geological models were reconstructed. The reconstruction of the stratigraphic framework offshore a volcanic coast provides a pathway to the investigation of the stratigraphic relationships between inter-eruptive sedimentary deposits and volcanic units, and permits the assessment of a wide and continuous chronostratigraphic framework in a complex area. Furthermore, the onshore-offshore correlation of the main Holocene volcanic units allows us to better estimate their areal distribution, a critical factor in the hazard evaluation of a coastal volcanic area. The application of seismic volcano stratigraphy illustrates the remarkable possibilities that the study of submarine volcanic fields offers.