Geomorfologia strutturale e domini di frattura dei fondali marini pericostieri dell’Isola di Procida (Campi Flegrei insulari, Italia meridionale)

Abstract

Putignano M.L. & Schiattarella M., Structural geomorphology and fracture system of the pericoastal sea floor of the
Procida Island (Insular Phlegraean Fields, southern Italy). (IT ISSN 0394-3356, 2010)
Sea floors surrounding Procida Island in the Bay of Naples have been studied from a morpho-structural point of view. Such a study has
been based on both direct survey of the submarine environment (up to the depth of 30 m) and seismic lines and echographic data
interpretation, and allowed us to realize an accurate geomorphological map of the pericoastal areas. Marine recent deposits, tectonic
morpho-lineaments, submarine erosional terraces, submerged notches and other submerged sea level markers have been mapped, so contributing to define the Holocene morpho-evolutionary picture of the Phlegraean offshore. The good fit between the submarine fracture system and the inland fault and fracture pattern suggests that the investigated coastal marine areas underwent the same lateQuaternary structural history of the nearby continental region. In addition, the recognition of several base-palaeolevels of the erosion allows to better define the interplay among sea-level changes, tectonics, and volcanogenic vertical movements. Archaeological data, ages of the volcanic products, their morpho-stratigraphic relationships with the submarine erosional terraces and other geomorphological constraints permit now a suitable chronological attribution to the different orders of land surfaces, making more reliable the calculation of the subsidence rates and helping the comprehension of the morpho-evolutionary trend of the study area.
The planimetric geometry of the strain field has been achieved by both submarine survey and morphostructural analysis: it clearly
shows en echelon style, consisting of three dimensionally similar fault-bounded sectors (Canale di Procida, Isola di Procida p.p. and
Promontorio di Solchiaro - Isola di Vivara - Canale di Ischia). From a physiographic viewpoint, such sectors result separated by E-O to
N120°-striking faults producing an apparent dextral offset. It is likely that they may represent transfer structures due to extensional
deformation by NNE-SSO-striking master faults and, therefore, featured by a “passive” left-lateral slip. The fault set displacing the
Neapolitan Yellow Tuff in the Capo Posillipo area and absent in the Procida Island area is N50-60° oriented. Such a trend also characterizes joint sets affecting submarine outcrops associated to hydrothermal phenomena. Then, one can conclude that this trend represent very recent structures, cut only by erosional surfaces located at a depth of 14/-15 m and attributed to the Middle Bronze Age. The subsidence rate calculated for five different orders of submarine erosional surfaces is apparently constant, showing always values
around 4-5 mm/y and so suggesting a regular evolution trough the time of the studied pericoastal system, characterized by the submersion of portions of coastal sectors by continuous and invariable volcano-tectonic subsidence. Yet, using the Post-Holocene sealevel rising curve to set the eustatic correction, it is possible to obtain a more articulated picture of the morpho-evolutive sequence,
characterized by alternating periods of different subsidence rates. This scenario seems to be more realistic in an area of complex interplay between tectonics and sea-level changes such as the Phlegraean Fields.