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SEDIMENTARY DYNAMICS OF THE MARETTIMO CONTINENTAL SHELF AND MARETTIMO CHANNEL (EGADI ISLANDS – WESTERN MEDITERRANEAN): ANALYSIS OF DEPOSITIONAL AND EROSIONAL FEATURES.
Full text linkSedimentary dynamics of the Marettimo continental shelf and Marettimo Channel (Egadi Island – Western Mediterranean), have been unveiled based on the erosive and
depositional features observed at the seafloor.
Different morphologic features were recognized through side scan sonar, multibeam and high-resolution seismics, acquired in the framework of national Research Projects
(CARG, GebecSud, MaGIC) carried out by the Department of Earth and Marine Science (former Department of Geology and Geodesy) of the University of Palermo. Sediment
samples have been also collected and analyzed.
The Egadi Islands are part of the NW Sicilian offshore, and belong to the mountain chain that connects the Sicilian chain to the Maghrebides one. The Marettimo Island
represents an isolated portion of the Egadi continental shelf and is separated from the rest of the archipelago by the Marettimo Channel.
Previous studies allowed to recognize different kind of sedimentary structures along the seafloor. Lo Iacono and Guillén (2008) described extensive field of subaqueous dunes
(Ashley, 1990) along the Marettimo inner shelf, forming on gravelly and pebbly sediments and related to strong storm events (H:5.5 m, T: 12 s). Larger dunes have been
observed in the north-western sector of the inner shelf with wavelengths ranging from 1 to 2.5 m, heights between 15 cm and 30 cm and extending laterally for hundreds of
meters. Moreover in the north-eastern sector of the inner shelf, sorted bedforms have been detected at a depth of 40 m: they are characterized by a width varying between
15 m and 50 m and a length that reaches hundreds of meters.
In the south-eastern sector of the Marettimo outer shelf, Colantoni et al. (1993) map two groups of sedimentary structures. In the same area, Lo Iacono (2004) recognized
two-dimensional and three-dimensional subaqueous dunes. 2D dunes are found at depths between 60 and 90 m and show a wavelength variable between 15 and 50 m. 3D
dunes, which are found at a depth of 80 m, are characterized by a wavelength of 30 m and a lateral extent of 50 m.
Morphological evidences of a strong hydrodynamic regime come also from the morphobathymetric analysis of the Marettimo Channel, that is a 24 km long submarine valley
oriented NNW-SSE, with a depth ranging from a minimum of 180 m to a maximum of 370 m and a width from 2 km to 14 km. Inside the channel, south of its narrowest point,
a 180 m deep bathymetric threshold separates two areas, which deepens towards opposite directions: north-west and south. The flanks of the sector that deepens towards
the NW are affected by mass-wasting features (Lo Iacono et al., 2007). The western flank of the channel, which delimits the Marettimo continental shelf, is carved by gullies,
making the shelf-edge very uneven. Gullies develop to a maximum depth of 280 m and have a length of 250 m and a width of 50 m. At the bottom of the channel a linear
incision 20 m deep, 400 m wide and almost 3 km long, is probably generated by erosive bottom currents.
On the whole, the morpho-sedimentary structures here described reveal a strong hydrodynamic regime. The morphological and textural features of the bedforms observed on
the Marettimo inner continental shelf suggest the occurrence of sporadic medium to strong storm events coming from western sectors. The morphological characteristics of
the Marettimo Channel reveal the occurrence of strong bottom currents probably related to the severe interchange of water masses between the Tyrrhenian Sea and the Sicily
Channel.
References:
Ashley, G., 1990. Journal of Sedim. Petrology 60, 160–172.
Colantoni, P., Ligi, M., Morsiani, M.P., Penitenti, D., 1993. UNESCO Reports in Mar. Science 58, 93–98.
Lo Iacono, C., 2004. Università di Napoli ‘‘Federico II,’’ Naples, Italy. Ph.D. Thesis, 150pp...
Lo Iacono, C., Catalano, R., Agate, M., 2007. VI Conv. FIST GeoItalia, Rimini (Italy), 12-14 Sept.
Lo Iacono C., Guillén J., 2008. Continental Shelf Research 28, 245–256
Bathy-morphological analysis of submarine canyons across the north-western Sicily continental slope
No full textWe present here the results of the morpho-bathymetric analyses of the main submarine canyons along the upper slope
off the north-western Sicily. This region developed during the Neogene as the transition area between the Sicilian fold
and thrust belt and the Tyrrhenian basin realm. Along the upper slope, a dense network of submarine canyon develops
from 80 m water depth up to more than 2000 m, showing a large variability of sizes and morphology. In this area
submarine canyons play a crucial role related to the along-slope sedimentary transport and are among the most distinctive
features of the submarine seascape.
This study is based on a quantitative analysis of a high resolution multibeam data set of the north-western Sicily
offshore integrated with the topographic DEM of the adjacent continental region. Very different canyon-related
morphological features along the study area mainly suggest the occurrence of top-down gravitational processes along
canyons likely originated through a bottom-up evolution. By means of high resolution bathymetric data, we: i) described
the main morphological features of submarine canyons; ii) measured the main morphometric parameters along canyon
longitudinal profiles; iii) calculated the extension of different lithology outcropping on the river catchment areas
corresponding to distinct river-fed canyons. For each analyzed canyon a chart was built in which bathymetric longitudinal
profile, catchment area extension and gradient longitudinal profile have been reported.
Quantitative analyses of longitudinal profiles reveal that the morpho-sedimentary evolution of mapped canyons is
comparable to the corresponding fluvial environment, although presenting some differences.
Integrated analysis of offshore data and river catchment areas suggest that the continental slope structural setting as
well as the outcropping lithologies could be relevant control factors on the morpho-sedimentary evolution of the NW
Sicilian canyons
Habitat mapping of VMEs along the inner shelf regions of the south-western Tyrrhenian margin (southern Mediterranean): a geo-statistical predictive approach
Full text linkThe main aim of this work is to statistically predict the distribution of Vulnerable Marine Ecosystems (VMEs) along the continental shelf regions of the northern Sicilian margin (southern Mediterranean).
The considered habitats, already mapped in the area on a qualitative base, are the Posidonia oceanica and Cymodocea nodosa seagrasses and the Coralligenous biocenosis. Posidonia oceanica and Coralligenous are considered as VMEs owing to their value as environmental indicators and biodiversity hotspots in coastal marine areas. For this reason, several actions were aimed in recent years to their complete characterization and mapping.
The study area is located in the continental shelf of the northern Sicily margin, between the Cape San Vito (Gulf of Castellammare) and Cape Zafferano (Gulf of Palermo).
Different physical characteristics of the seafloor were extracted from a database acquired in recent years in the frame of official national cartography (CARG) and hazard assessment (MAGIC) Italian Projects, including geological and geophysical data (seabed sampling, ROV footage, multibeam bathymetry, backscatter maps, high resolution seismic reflection records)
The ultimate goal is to apply a statistical methodology allowing to predict the distribution of marine habitats from a “presence only” sampling dataset. This target was pursued by using a multidisciplinary approach, including abiotic (i.e. depth, morphological and hydrodynamic features, type of seabed) and biotic components (benthic communities) that define and characterize the mapped habitats.
Predictive maps are based on the Maximum Entropy model (MaxEnt), a statistical method based on punctual occurrence of specimen (presence-only). The punctual occurrence of the three habitats was already known, whilst we considered the bathymetry, seabed steepness, aspect, fluid escape, erosional areas and sediment type as physical features for the model.
The analysis was also aimed to test the performance of models obtained by choosing the training samples with different criteria. Therefore, different outputs (42 in total) have been produced by selecting samples on the basis of the area (regional analysis), the type of coasts (morphological) or randomly (random). Moreover, the models were built up both with only training samples either with training and test samples to obtain more constrained distribution patterns.
Almost all the created predictive models produced good performances, with statistical parameters (gain, AUC standard deviation) very positive on average. The models derived from the regional analysis resulted to be more performing than the others, with the random-derived being the worst. The response curves pointed out that bathymetry and sediment types are the most important physical features influencing the distribution of the mapped VMEs, whereas aspect and slope are not-independent variables. These outputs also provided important information and constraints on the favorable environmental conditions for the three habitats.
Results from this preliminary statistical modeling appears potentially useful in the evaluation of important environmental parameters, allowing to draw the broad distribution of marine habitats in areas where only presence data are available, and can represent a contribution in the design and monitoring of marine protected areas
Submarine canyon of the north-western Sicilian offshore (Southern Tyrrhenian Sea): variability in morphologies, sedimentary processes and tectonic settings
No full textControlli stratigrafici e tettonici sull'evoluzione morfo-sedimentaria dell'offshore della Sicilia nord-occidentale durante il Quaternario
No full textA geo-statistical predictive approach to the Habitat mapping of Vulnerable Marine Ecosystems along the northern Sicily inner continental shelf (southern Mediterranean)
Full text linkThe main aim of this work is to statistically predict the distribution of Vulnerable Marine Ecosystems (VMEs) along the continental shelf regions of the northern Sicilian margin (southern Mediterranean).
The considered habitats, already mapped in the area on a qualitative base, are the Posidonia oceanica and Cymodocea nodosa seagrasses and the Coralligenous biocenosis. Posidonia oceanica and Coralligenous are considered as VMEs owing to their value as environmental indicators and biodiversity hotspots in coastal marine areas. For this reason, several actions were aimed in recent years to their complete characterization and mapping.
The study area is located in the continental shelf of the northern Sicily margin, between the Cape San Vito (Gulf of Castellammare) and Cape Zafferano (Gulf of Palermo).
Different physical characteristics of the seafloor were extracted from a database acquired in recent years in the frame of official national cartography (CARG) and hazard assessment (MAGIC) Italian Projects, including geological and geophysical data (seabed sampling, ROV footage, multibeam bathymetry, backscatter maps, high resolution seismic reflection records).
The ultimate goal is to apply a statistical methodology allowing to predict the distribution of marine habitats from a “presence only” sampling dataset. This target was pursued by using a multidisciplinary approach, including abiotic (i.e. depth, morphological and hydrodynamic features, type of seabed) and biotic components (benthic communities) that define and characterize the mapped habitats.
Predictive maps are based on the Maximum Entropy model (MaxEnt), a statistical method based on punctual occurrence of specimen (presence-only). The punctual occurrence of the three habitats was already known, whilst we considered the bathymetry, seabed steepness, aspect, fluid escape, erosional areas and sediment type as physical features for the model.
The analysis was also aimed to test the performance of models obtained by choosing the training samples with different criteria. Therefore, different outputs (42 in total) have been produced by selecting samples on the basis of the area (regional analysis), the type of coasts (morphological) or randomly (random). Moreover, the models were built up both with only training samples either with training and test samples to obtain more constrained distribution patterns.
Almost all the created predictive models produced good performances, with statistical parameters (gain, AUC standard deviation) very positive on average. The models derived from the regional analysis resulted to be more performing than the others, with the random-derived being the worst. The response curves pointed out that bathymetry and sediment types are the most important physical features influencing the distribution of the mapped VMEs, whereas aspect and slope are not-independent variables. These outputs also provided important information and constraints on the favorable environmental conditions for the three habitats.
Results from this preliminary statistical modeling appears potentially useful in the evaluation of important environmental parameters, allowing to draw the broad distribution of marine habitats in areas where only presence data are available, and can represent a contribution in the design and monitoring of marine protected areas
Submarine canyons of north-western Sicily (Southern Tyrrhenian Sea): Variability in morphology, sedimentary processes and evolution on a tectonically active margin
Full text linkSwath-bathymetry, mono-channel and multi-channel seismic reflection records acquired during the last two decades on the northern Sicilian margin have unveiled a dense network of submarine canyons within the depth range of 80–2100 m. The canyons display a relevant variability in their geometry, morphology and sedimentary processes. The margin shows a young, tectonically active shelf to slope setting, linking the Sicilian–Maghrebian Thrust Belt to the Tyrrhenian oceanic realm, developed during the Neogene–Quaternary time span. The aim of this study is to highlight the main governing factors that contributed to the evolution and differentiation of the northern Sicilian canyons, mainly focusing on the Gulf of Palermo and on the Gulf of Castellammare. Tectonic control is more evident in the canyons of the Gulf of Palermo, with submarine landslides retrograding on a steep slope and mainly controlling their evolution. Otherwise, canyons, tributaries and gullies mapped in the Gulf of Castellammare developed on a less steep substrate and display sinuous to meandering paths, with a relevant role of coastal/shelf sedimentary inputs and downslope turbidity processes in their formation. Results suggest that, despite the geographically close proximity of the two study areas, the different structural settings of the Castellammare and Palermo Basins are mainly responsible for canyon variability. Data indicate likely on-going uplift and tilting movements along the Sicilian margin, influencing the development of the studied canyons, which have probably been more active during the Quaternary glacial maxima than they are in the present day
Benthic habitat characterisation of soft-bottom continental shelves: Integration of acoustic surveys, benthic samples and trawling disturbance intensity
No full textEleven sites were located on Mediterranean continental shelves to explore the link between the physical characteristics and epibenthic fauna from soft-sediment habitats. These sites, at 32–82 m in depth, were associated with fishing grounds and the trawling intensity was estimated at the site scale to assess the effects of trawling on benthic communities. Each site was surveyed with Multi-Beam (bathymetry and backscatter), side-scan sonar, benthic grabs and a surface dredge. The sites were clustered in three habitat types. Habitat 1, with moderate trawling disturbance, was characterised by homogeneous mud and associated epifauna that was also highly homogeneous across sites. Habitat 2, with sandy mud and scattered gravel and rocks, had a high abundance of sessile suspension feeders that probably attach to the coarser substratum and benefit from the low fishing disturbance in these sites. Habitat 3 included sites with heterogeneous sediments with maërl as the prevailing biocenosis and having the highest species richness, despite being subjected to variable trawling intensity. Statistical models were used to relate environmental parameters and the species abundance. More than 3 physical variables were necessary to explain the epifaunal patterns across sites, including the percentage of mud, sediment heterogeneity and fishing effort. These analyses are an essential step for extrapolating information from benthic samples to the larger scale of habitats, mapped through acoustic surveys. Despite this, a good integration is required between the mapping of physical habitat distribution and the ecological knowledge of communities
Geomorphological, trophic and human influences on the bamboo coral Isidella elongata assemblages in the deep Mediterranean: To what extent does Isidella form habitat for fish and invertebrates?
No full textWe analyzed what are the best ecological conditions for megafauna associated with the bamboo coral Isidella elongata based on the geomorphological, physical and trophic information taken in 3 stations (St1, St2, St3) off the southern Catalonian coasts at 620 m depth in June 2011. Results were compared with assemblage compositions recorded in past cruises (May 1992, 1994) at the same 3 stations. St1 was in a fishing ground exploited since the 1940s over a relatively wide slope at ca. 22 km from the nearest canyon head; St2 and St3 were on a narrower slope closer to canyon heads and to the Ebro river mouth than St1. I. elongata had formed (to May 1994, at least) a dense coral forest at St2–St3 (to ca. 255 colonies/ha at St3), and some isolated colonies (to ca. 0.9 colonies/ha) were still collected in 2011. Fish and invertebrate communities significantly differed between St1 and St2/St3, with two macrourid fishes (Trachrhynchus trachyrhynchus and Nezumia aequalis) and two decapods (Plesionika martia and Plesionika acanthonotus) more abundant at St2/St3. The following ecological indicators imply better food conditions for megafauna at St2–St3 and for I. elongata itself: (i) greater density of zooplankton (copepods, euphausiids, and others) as potential prey for planktivores (including I. elongata); (ii) greater biomass and mean weight of epifaunal and infaunal deposit feeders; (iii) higher feeding intensity, F, at St3 for benthos feeders (Phycis blennoides, N. aequalis and Aristeus antennatus). Also, at St2–St3 we found higher near-bottom turbidity (indicating particle resuspension: food for suspension feeders) and finer and more reduced (Eh) sediments. The results let us suggest that corals and accompanying fauna preferently found optimal ecological conditions in the same habitat, while habitat-forming capacity by I. elongata seemed weak to generate these conditions. Coral forests may enhance detritus accumulations around them, improving habitat conditions for benthos feeders (e.g. macrourid fish). At St3 our side-scan sonar recorded three types of tracks produced by trawler doors, which match with three identified vessels occasionally operating in the area. After this low fishing activity off the Ebro Delta since the mid-1990s, almost all colonies of I. elongata has been removed. However, this impact has hardly altered fish and invertebrate composition without any significant loss of diversity, pointing also toward a rather low capacity of I. elongata facies in forming habitat for megafauna on muddy bottoms of the Mediterranean slope
Submarine Geomorphology and Sedimentary Features around the Egadi Islands (Western Mediterranean Sea)
Full text linkThe physiography, the geomorphological features and the sedimentary bedforms offshore Egadi Islands (Italy) have been illustrated and mapped through an integrated analysis of high-resolution bathymetric, seismo-acoustic and sedimentological data. The study area is characterized by a wide, up to 25 km, continental shelf which is separated by a NNW trending linear incision, the Marettimo Channel, along which several erosional and depositional features have been detected and mapped. Sedimentary prograding wedges were detected at water depths between 100-125 m along the shelf margin, which accumulated during sea level fall and lowstand stages of the last glacio-eustatic cycle (post- MIS 5.5). The study detected several slope breaks defining scarps across the continental shelf, which were interpreted as coastal cliffs that originated during the post-LGM eustatic sea level rise. Several fields of different types of sedimentary bedforms, including 2-D and 3-D hydraulic dunes and sorted bedforms, were found across the continental shelf, providing evidence of a high hydrodynamic regime affecting the seafloor. Further on, the study recognized erosive and depositional features related to bottom currents (contourites) in the Marettimo Channel.
These findings provide a better understanding of the morpho-sedimentary evolution of the Egadi Islands offshore in the latest Quaternary. Moreover, they offer essential scientific support for effectively managing the most valuable priority habitats for conservation , such as Posidonia oceanica meadow and coralline algae bioconstructions (Coralligenous habitat)
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