GNGTS 2013 - Atti del 32° Convegno Nazionale

Marine geological units. Several volcanic units of substrate have been distinguished, cropping out between the Procida islands, the promontories of Monte di Procida and Capo Miseno and the coastal cliffs off Nisida and Posillipo (Naples town), of a carbonate unit of substrate, cropping out in the Sorrento Peninsula off Massalubrense and of undifferentiated carbonate and volcanic substrates, distinguished in the offshore area based on geophysics. The Late Quaternary marine geological units are herein described as it follows (Ispra, 2011). The littoral environment is characterized by different types of deposits, which characterize the high relief coasts and the low relief coasts. The toe of cliff deposits, representative of high relief coasts, represent the terms of passage among the sediments of the volcanic units representing the submerged cliffs and the sands and gravels of inner shelf, sometimes with the interposition of submerged cliff sandy belts. In some cases they represent relict isolated bodies and are not yet linked with the supplying reliefs. For the sectors of low coasts, the deposits of submerged beach are represented mostly by sediments which characterize the deposition of the actual beaches. They represent the natural extension in the submerged sectors of the beach deposits occurring along the emerged coastal belt. These deposits join seawards the inner shelf sediments and sometimes occur in narrow belts interposed among the toe of cliff deposits and the inner shelf ones. The littoral environment is characterized by beach rock deposits (Ispra, 2011) occurring in the Ciraccio Bay (Procida island) and in the Genito Gulf (Vivara, Procida). In the first site they are represented by cemented micro-conglomerates composed of volcanic clasts, in the second one they are represented by coarse-to-middle-grained sandstones (Ispra, 2011; De Muro and Orrù, 1999; Kelletat, 2006; Putignano et al. , 2009; Putignano and Schiattarella, 2010). The deposits of submerged beach are characterized by different lithologic associations, from gravels to fine-grained sands. The grain variations observed in the sediments are related to the hydrodynamic regimes and the wave motion. The distribution of the beach sediments is strictly connected with the morphological characteristics of the coasts and generally represent pocket beach deposits. They are composed of volcanic gravels and litho- bioclastic sands and middle-to-fine-grained litho-bioclastic sands. The deposits of coastal cliff are often represented by rock fall deposits, composed of heterometric blocks, often tufaceous in nature, mainly at the toe of the coastal cliffs of S. Margherita promontory (Vivara, Procida) and Punta Solchiaro (Procida). Another type is represented by the reworked rock fall deposits, composed of heterometric gravels and lying as isolated bodies on the sea bottom, as at Marina Grande, Ciraccio and Pozzo Vecchio (Procida). The continental shelf is the depositional area localized between the littoral deposits and the shelf break, localized at variable depths among 130 and 170 m. In the Naples Bay this element is localized in correspondence to the retreating heads of the Dohrn and Magnaghi canyons. Different lithofacies associations occur in this environment, related to the hydrodynamic regimes and sedimentary supply. Sandy belts occur, elongated according to the lines of great steepness of the sea bottom. Wide fields of ripples and mega-ripples are diffused in the bathymetric belt among the 20 and 50 meters of water depth. The continental shelf deposits are mainly litho-bioclastic and characterized by different lithological associations, from the gravels to the sands and the pelites and volcanic grains composed of whole pumices or pumice fragments, tuff fragments and scorias. The bioclasts are composed of fragments of Molluscs shells, Echinoderms or benthic foraminifers. The prevalent lithofacies is represented by gravels, sandy gravels and litho-bioclastic coarse grained sands, often occurring with Posidonia Oceanica mattes (Ispra, 2011). These associations characterize wide areas of the continental shelf surrounding the Procida island and the Procida channel. Depositional discontinuities are due to the outcropping of rocky substrates, as in the Pozzo Vecchio and in the Corricella areas. A second shelf lithofacies is represented by the middle-to-fine-grained lithobioclastic sands. The main components are represented by pyroclastic fragments (pumices and lapilli) and bioclasts, often abundant. These deposits individuate wide areas of the remnant part of the inner shelf, characterized by low energy sedimentation in flat sea bottoms. These facies 177 GNGTS 2013 S essione 3.3