Gemma Aiello

Marine Geology and Morphobathymetry in the Bay of Naples (South-Eastern Tyrrhenian Sea, Italy)

Recent multibeam bathymetry (Elac, Bottomchart MK2) and high resolution seismics (Subbottom Chirp and 1–4 kJ Sparker source), acquired in the frame of an on-going programme of sea-floor mapping of Naples and Salerno Bays (south-eastern Tyrrhenian margin, Italy) and financed by the National Geological Survey of Italy, allows to put new insights into the recent evolution of the bay. The morphology and stratigraphy of the continental shelf and slope appear strongly controlled by the interplay of volcanism and canyoning that acted along the Magnaghi and Dohrn axes. Detailed bathymetry reveals the complexity of the drainage pattern which consists of a previously unknown, dense network of minor tributary channels. At places, the Dohrn and Magnaghi canyon walls are intensively affected by slope instability, as evidenced by numerous submarine slides and scars involving large volumes of sediments. Previously unreported mound-shaped morphological highs (“Bacarozzi” Facies), Holocene reworked sediments and sea-bottom creep appear on acoustic Chirp profiles in the inner sectors of the bay and seem to be related to volcano-sedimentary processes. On the contrary, sedimentation over the shelf at the southern edge of the bay (Sorrento-Capri) seems less influenced by volcanic activity and seabed features include Late Pleistocene regressive sand bodies and Holocene patch reefs, coastal dunes and depositional terraces.

Quaternary structural evolution of terracina and gaeta basins (Eastern Tyrrhenian margin, Italy)

In the Terracina and Gaeta basins Quaternary sediments are displaced by normal faults, which affect also the Meso-Cenozoic tectonic units of the acoustic basement. The extensional tectonics is characterized by normal faults systems trending NE-SW and E-W. In the Terracina basin, roughly N-S oriented, half-graben structures are downthrown seaward through normal faults; the Gaeta extensional basin, E-W oriented, has two main depocenters and is bounded to the north and to the south by E-W trending normal faults and to the east by a NW-SE trending normal fault.RiassuntoI bacini di Terracina e Gaeta mostrano un significativo controllo tettonico sulla sedimentazione quaternaria, causato dalla presenza di faglie normali: esse dislocano le unità tettoniche meso-cenozoiche che rappresentano il basamento acustico. Sistemi di faglie normali ad andamento NE-SW e E-W determinano nel bacino di Terracina una struttura di tipo semi-graben orientata N-S e ribassata verso mare da faglie dirette. Il bacino di Gaeta rappresenta un bacino estensionale ad andamento E-W, articolato in due principali depocentri e delimitato verso nord e verso sud da faglie normali ad andamento E-W e verso est da una faglia diretta ad andamento NW-SE.

Seismic Tomography Experiment at Italy's Stromboli Volcano

Stromboli Island, located in the southern Tyrrhenian Sea, is the emerged part (about 900 meters above sea level) of an approximately 3-kilometer-high stratovolcano. Its persistent Strombolian activity, documented for more than 2000 years, is sometimes interrupted by lava effusions or major explosions. Despite the number of recently published geophysical studies aimed at clarifying the volcanos eruption dynamics, the spatial extent and geometrical characteristics of its plumbing system remain poorly understood. In fact, knowledge of the inner structure and the zones of magma storage is limited to the upper few hundred meters of the volcanic edifice [Chouet et al., 2003; Mattia et al., 2004], and P and S wave velocity models are available only in restricted areas [Petrosino et al., 2002].

Three-dimensional magneto-seismic reconstruction of the ‘Torre del Greco’ submerged volcanic structure (Naples Bay, Southern Tyrrhenian Sea, Italy): implications for Vesuvius’s marine geophysics and volcanology

A three-dimensional reconstruction of a large volcanic structure located offshore the town of Torre del Greco (Naples Bay, Southern Tyrrhenian Sea, Italy) and representing the seaward prolongation of the Vesuvius volcano has been carried out using integrated geological interpretation of existing densely-spaced high-resolution seismic and magnetic profiles. This reconstruction has provided new insights into the knowledge of marine geophysics and volcanology of Vesuvius, one of most studied volcanoes in the world. Seismic stratigraphy of the volcanic structures shows acoustically-transparent seismic facies and high contrasts of acoustic impedance with respect to the overlying sediments. The structures have mound-shaped external geometry and average dimensions measurable in terms of kilometres. The base of the Torre del Greco volcanic structure overlies the volcanic seismic unit correlated to the ‘Campanian Ignimbrite’ pyroclastic flow deposits. Consequently, no contrast of acoustic impedance between the two volcanic units is clearly evident on the seismic profiles. The top of the structure is irregular and eroded and shows several culminations. The three-dimensional reconstruction of the Torre del Greco structure has been carried out using seismic constraints and correlations of volcanic structure to bathymetry. The sea floor topography is compared to the top of the Torre del Greco volcanic structure represented by contour depth of corresponding seismic horizons. Proceeding from south-east to north-west there is a good correspondence between the sea floor topographic surface and the top of the volcanic structure, which does not crop out at the sea-bottom. The rising of the volcanic structure in proximity to the sea-bottom corresponds to the occurrence of topographic undulations of up to ten metres. This evidence is confirmed by the interpretation of seismic profiles, showing three main vertical culminations of the volcanic structure, where the overlying sediment drape is significantly reduced. These culminations are linked to magnetic anomaly extremes, having values ranging between 250–350 nT. A striking coincidence between the long-shaped topographic high on the sea floor (towards the east) and the high in the top of the volcanic structure underneath can be explained as a consequence of sea floor deformation due to the underlying volcanic culminations. Smaller volcanic mounds, buried and fossilized by marine sediments, are not related to any magnetic anomaly, probably due to their composition of volcanic tuffs.

High resolution seismic data coupled to Multibeam bathymetry of Stromboli island collected in the frame of the Stromboli geophysical experiment: implications with the marine geophysics and volcanology of the Aeolian Arc volcanic complex (Sicily, Southern Tyrrhenian sea, Italy)

New high resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording active seismic data and tomography of the Stromboli Island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli Island is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area compared to the volcanologic setting of the Aeolian Arc volcanic complex. Due to its high resolution the new Digital Terrain Model of the Stromboli Island gives interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of Subbottom Chirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution. They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the intriguing geology of the Aeolian Arc, a volcanic area still in activity and needing improved research interest.

Interactions between Late Quaternary volcanic and sedimentary processes in the Naples Bay, Southern Tyrrhenian sea

The interactions between Late Quaternary volcanic and sedimentary processes in the Naples Bay, Southern Tyrrhenian sea, are here discussed through the results of the marine geological survey at the scale 1:25.000. The example of the geological map n. 465 “Isola di Procida”, herein presented, has put in evidence the stratigraphy of marine Quaternary deposits and related volcanic seismic units. The volcanic deposits cropping out in the Procida island have been explained as the result of eruptions of local eruptive centres. The geological survey carried out onshore indicates the occurrence of several pyroclastic units linked to the eruptive activity of the Ischian and Phlegrean volcanic complexes, interstratified with the products erupted by local volcanic centres. The occurrence in the pyroclastic sequences of Ischia and Procida islands of several marker horizons and their stratigraphic correlations have allowed to reconstruct the volcanological evolution of the two islands and the interactions with sedimentary processes at the scale of the whole Tyrrhenian margin. Four geological maps at the scale 1:25.000 covering the whole Naples Bay have been reconstructed based on the interpretation of marine geological and geophysical data. The stratigraphic relationships between the seismic units and the eruptive deposits have testified the activity of several monogenetic volcanic centers, whose products are interstratified with marine and continental deposits of the Late Quaternary depositional sequence.

The Southern Ischia canyon system: examples of deep sea depositional systems on the continental slope off Campania (Italy)

The Southern Ischia canyon system has been investigated in detail through Multibeam bathymetry and Sparker seismic data and has been put in the geological framework of the deep sea depositional systems off the Campania region. The geological and geomorphological characteristics of the canyon system have been also compared with the characters of the Mediterranean submarine canyons and with the deep sea depositional systems of the Tyrrhenian sea. The Southern Ischia canyon system engraves a narrow continental shelf from Punta Imperatore to Punta San Pancrazio, being limited southwestwards from the relict volcanic edifice of the Ischia Bank. It consists of twenty-two drainage axes, whose planimetric trending has been reconstructed in a sketch morphological map realized through the geological interpretation of Multibeam bathymetry. While the eastern boundary of the canyon system is controlled by extensional tectonics, being limited by a NE-SW trending (anti-Apenninic) normal fault, its western boundary is controlled by volcanism, due to the growth of the Ischia volcanic bank. Submarine gravitational instabilities also acted in relationships to the canyon system, allowing for the individuation of large-scale creeping at the sea bottom and hummocky deposits already interpreted as debris avalanche deposits. Quaternary marine seismic sequences have been reconstructed through a densely spaced seismic grid recorded through a Sparker multitip seismic source, allowing for a detailed observation of steep erosional slopes occurring on the southern flank of the island and related deep sea depositional systems. Important implications of this study will regard the coastal monitoring and beach nourishment of the southern flank of the island, being involved by a strong erosion of marine and coastal systems.

On the occurrence of the Neapolitan Yellow Tuff tephra in the Northern Phlegraean Fields offshore (Eastern Tyrrhenian margin; Italy)

A main volcanic marker has been identified for the first time on the continental shelf of the northern Phlegraean Fields in the Gulf of Gaeta (Campania region, eastern Tyrrhenian margin, Italy) by means of Subbottom Chirp profile grid and stratigraphic analysis of a core collected on the slope. In the seismic sections, the core bottom corresponds to the top of a continuous and parallel reflector (V) interbedded within the transgressive deposits of the Late Quaternary-Holocene depositional sequence. The Transgressive System Tract deposits are particularly thick compared to the majority of the transgressive deposits of other shelf settings. This might be due to the input of pyroclastic and volcaniclastic deposits related to the intense eruptive activity of the Campania Plain during the Late Pleistocene-Holocene time span. Undulations and pockmarks are the main morphological features of the sea floor and they might be linked to gas uprising, widely detected in the study area. The V reflector is located on the shelf from northeast to southwest at different depths, ranging from 10 ms (about 8 m) to 30 ms (about 25 m) below sea floor and it can be mapped down to the continental slope. The tephrostratigraphic analysis of this continuous reflector allowed to correlate it with the Neapolitan Yellow Tuff deposits emplaced at Phlegraean Fields at ca. 15 ka.

High-resolution seismic stratigraphy of the Gulf of Pozzuoli (Naples Bay) and relationships with submarine volcanic setting of the Phlegrean Fields volcanic complex

High-resolution seismic stratigraphy of the Gulf of Pozzuoli has been studied to discuss volcanological implications on geological evolution of the Phlegrean Fields volcanic complex. A new seismo-stratigraphic framework of the Gulf of Pozzuoli is provided based on the geological interpretation of Sparker profiles, showing thirteen seismic units. The seismo-stratigraphic analysis has evidenced that the marine units prevail in the eastern Pozzuoli offshore (Baia town) while the volcanic units prevail in the western Pozzuoli offshore (Pozzuoli town). Two deep volcaniclastic units appear to be related to the northern margin of the Pentapalummo Bank, a relict volcanic edifice located in the outer Pozzuoli shelf. The Pozzuoli basin filling is made up of five seismic units, marine in origin, whose internal configuration is mostly characterized by parallel reflectors. The marine units are overlain by three volcanic units, whose origin is probably pyroclastic, both due to their seismic facies and to their deposition in palaeo-morphological depressions. A wedge-shaped seismic unit, acoustically transparent, has been interpreted in the Gulf of Pozzuoli as the Neapolitan Yellow Tuff deposits. Lowstand and highstand deposits, pertaining to the Late Quaternary depositional sequence are, respectively, characterized by progradational and parallel seismic reflectors, located in the Gulf of Pozzuoli. Different models on the geological structure of the Phlegrean caldera and its present-day unrest state have been taken into account to improve the discussion of the volcanological aspects related with the seismo-stratigraphic setting of the Gulf of Pozzuoli, representing the submerged border of the caldera itself. In the frame of research themes pertaining to the volcanic geology of the Campania continental margin, a stratigraphic correlation between the Gulf of Pozzuoli and Ischia island volcanic areas, whose geological data have been previously collected, has been performed and is herein presented, highlighting new interesting implications and results on the geology of the Naples Gulf.

New insights on the late Quaternary geologic evolution of the Ischia Island coastal belt based on high-resolution seismic profiles

The study of the seismo-stratigraphic architecture of Late Quaternary-Holocene volcanic and sedimentary units in the Ischia Island offshore and their correlation with the coastal units of the adjacent onshore sectors allowed for a detailed reconstruction of the seismic stratigraphy of the northern, southern and western sectors of the island. Five (southern Ischia) to nine (western Ischia) seismic units and related seismic facies were identified. The volcanic areas and their detailed seismo-stratigraphic setting fit well in the geological context of a passive margin and confirm that the stratal architecture in the Ischia Island Quaternary marine deposits is controlled by the interaction between glacio-eustatic fluctuations, volcanism, tectonics and sedimentary supply.