Eleonora Martorelli

Bathy-morphological setting of Terceira Island (Azores) after the FAIVI cruise

High-resolution morpho-bathymetric data at 1:200,000 scale obtained during the FAIVI cruise (2011) and the resulting geomorphologic map of the Terceira island offshore area (central Azores, Portugal) are presented for the first time. The uneven morphology around Terceira is primarily related to volcanic features, such as linear and cone-shaped eruptive centres and lava flows. Such features are mostly concentrated on volcanic ridges and are aligned along preferential axes, suggesting a strong interaction between tectonics and volcanic processes. The occurrence of active tectonics is also demonstrated by systems of faults cutting the seafloor to the north, east and south of the island. Mapped erosive-depositional features include an insular shelf located at < 150 m water depth (wd), small landslide headwalls, erosive scarps, channelized features and crescent-shaped bedforms. The presented map may represent the base for a first-order geo-hazard assessment.

The role of Internal Solitary Waves on deep-water sedimentary processes: The case of up-slope migrating sediment waves off the Messina Strait

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Cannibalization of a Continental Margin By Regional Scale Mass Wasting: An Example From the Central Tyrrhenian Sea

A morpho-stratigraphic study carried out on the Western Pontine Archipelago continental slope (Eastern Tyrrhenian Margin) revealed a suite of instability/erosional features producing the complete cannibalization of a whole span of continental slope, from the shelf break down to the abyssal plain (located at 3600 m w.d.); only 2% of the whole area (2.000 sq. km) is not affected by these processes. One of the main controlling factors seems to be the slope gradient that produce different instability features, ranging from gravity-driven failure (simple and complex slides) to gravity-flow (debris and grain flows).

Mass Wasting Features on the Submarine Flanks of Ventotene Volcanic Edifice (Tyrrhenian Sea, Italy)

High-resolution multibeam bathymetry acquired around Ventotene and S. Stefano islands (eastern Pontine Archipelago, Italy) enabled us to map main mass wasting features affecting their submarine portions. Large-scale instability morphological features are absent (apart from a 4 × 2.5 km caldera in the western sector), whereas 126 landslide scars of 100-m of length scale were identified between 130 and 1,150 m of water depth (wd). Two main groups of scars can be distinguished: the first one affects the edge of the insular shelf between 130 and 260 m wd. The second group affects the lower slope and surrounding basins, representing cases of retrogressive failure at the heads of channelized features. The different morphological relief of the scars coupled with the recognition of crescent-shaped bedforms made it possible to distinguish two mass-wasting/erosive stages and consequently to map the more active sectors of the edifice. The future evolution of the mass wasting processes will produce the enlargement of erosive sectors with possible formation of large channels, which will carve wide sectors of the edifice, as suggested by available geological constraints and by comparison with the nearby and older western sector of the Pontine archipelago, where a more mature organization of mass wasting processes is observed. The present study can provide useful insights for hazard assessment and future planning of risk mitigation in such islands that are densely populated and touristically exploited during the summer months.

Chapter 12 Overview of the variability of Late Quaternary continental shelf deposits of the Italian peninsula

Abstract This paper documents the Late Quaternary (120 ka BP–present) stratigraphic architecture of Italian continental shelves through the interpretation of single-channel, very high-resolution seismic reflection profiles and from data derived from published studies, by using the high-resolution sequence stratigraphy framework. The result of this analysis provides a detailed reconstruction of the variability of shelf stratigraphy in relation to differences in physiography, sediment supply, structural framework and local factors. We distinguish four stratigraphic types: (1) wide shelves with high sediment supply (e.g. the central Adriatic and the central-northern Tyrrhenian shelves); (2) wide but sediment-starved shelves (e.g. the southern Latium shelf); (3) narrow shelves with high sediment supply (e.g. shelves located in the Ionian and southern Tyrrhenian Sea); and (4) narrow and sediment-starved shelves (shelves located around islands and archipelagos). Besides physiography, sediment supply and vertical movements, local factors and specific processes play a significant role in determining Late Quaternary stratal architecture and sedimentary facies. For example, the attributes of antecedent topography commonly seem to govern the formation and preservation of transgressive deposits, whereas the formation and preservation of falling stage and lowstand systems deposits can be hindered by the presence of canyons indenting the shelf edge and/or slope instability.

New Insights on Failure and Post-failure Dynamics of Submarine Landslides on the Intra-slope Palmarola Ridge (Central Tyrrhenian Sea)

Newly collected multibeam and seismic data on the intra-slope Palmarola ridge show widespread pockmarks and landslide-related morphologies along its flanks. In detail, two main types of slope failures were identified: disintegrative-like and cohesive like landslides. The first type is characterized by a complex of small, nested scars affecting the steep and tectonically-controlled eastern flank of the ridge, suggesting a genesis related to retrogressive processes. The cohesive landslides affect the northern flank of the ridge and are characterized by larger scars, where material was not completely evacuated, and well-defined debris deposits at their base, with the development of pressure ridges. Tectonic activity and slope gradients represent the main controlling factors for the development of instabilities; moreover, we noted a relationship between pockmarks and landslide scars.

Spiculosiphon oceana (Foraminifera) a new bio-indicator of acidic environments related to fluid emissions of the Zannone Hydrothermal Field (central Tyrrhenian Sea)

The new record of a shallow-water submarine hydrothermal field (<150 m w.d.) in the western Mediterranean Sea (Tyrrhenian Sea, Italy) allows us to study CO2 fluid impact on benthic foraminifers. Benthic foraminifers calcification process is sensitive to ocean acidification and to local chemical and physical parameters of seawater and pore water. Thus, foraminifers can record specific environmental conditions related to hydrothermal fluids, but at present their response to such activity is poorly defined. The major outcome of this study is the finding of a very uncommon taxon for the Mediterranean Sea, i.e., the Spiculosiphon oceana, a giant foraminifer agglutinating spicules of sponges. This evidence, along with the strong decrease of calcareous tests in the foraminiferal assemblages associated to hydrothermal activity, provides new insights on the meiofauna living in natural stressed environment. In particular, observations obtained from this study allow us to consider S. oceana a potential tolerant species of high CO2 concentrations (about 2-4 times higher than the normal marine values) and a proxy of acidic environments as well as of recent ocean acidification processes.