1,720,975 research outputs found
La sismica ad alta risoluzione digitale a mare: vincoli teorici, elaborazione numerica, nuovi sviluppi (High-resolution marine digital seismic method: theoretical constrains, digital processing, new developments )
No full textMarcello Bernabini, Rinaldo Nicolich, Luigi Sambuell
Biogeophysical Classifìcation of Seafìoor Seeps at a Carbonate-Hydrate Mound, Northern Gulf of Mexico
No full textLocated on the continental slope in 900m of water, Woolsey Mound dominates seafloor morphology at Mississippi Canyon 118. The carbonate-hydrate mound is the site of the Gulf of Mexico Hydrates Research Consortium’s seafloor observatory to investigate and monitor hydrographic, geophysical, geological, geochemical and biological processes of the hydrocarbon system, northern Gulf of Mexico. Spatial and temporal variability of processes that produced the mound - venting fluids, formation/dissociation of hydrates, formation of authigenic carbonate and of micro and macrofaunal communities - are unknown and form the basis of several investigations at the site.
Innovative survey and monitoring systems, sensors, and tools have been developed to extract samples and data to unravel the history, character and composition of the site. This study represents an attempt to integrate results of extensive geophysical studies with recent studies of the macrofauna thriving at the site, and to use the results to develop a system of vent classification for use in evaluating the subseafloor hydrocarbon system.
Seafloor morphology and geology have been characterized integrating high resolution swath bathymetry, acoustic imagery, seafloor video and sediment, water column, and pore-water samples. AUV bathymetric surveys were completed in 2005 and 2009; video images, photographs, core samples and water samples were collected during cruises from 2002 - 2010.
Seismo-acoustic data have been directed at maximizing definition at various depths. Deep data show a salt body underlying Woolsey Mound; crestal faults emanating from the salt body infrequently but notably intersect the seafloor. High frequency chirp and surface-source-deep-receiver data reveal many intersections of antithetical faults with the seafloor. These have been mapped over seafloor bathymetry determined from multibeam surveys.
Outcropping hydrates, fluid-migration features and seafloor communities- identified and described from numerous types of imagery - have been mapped. These maps have been combined/overlain on the bathymetry/fault maps to produce a biotypes-seep map from which we have identified and differentiated types of seeps. Community complexity is used as a proxy for seep duration/age while specific community components are believed to reflect composition of seep fluids. Although preliminary, this approach represents a novel classification system for seafloor hydrocarbon seeps
The Zannone Giant Pockmark. First evidence of a giant complex seeping structure in shallow-water, central Mediterranean Sea, Italy
No full textAn active giant pockmark located offshore Zannone Island (central Tyrrhenian Sea, Italy), is analyzed by very high resolution multibeam bathymetry, high resolution seismic profiles, ROV video observations, sediment and water sampling. The active fluid emission area is located on the outer shelf, between 110 and 130 m water depth, and affects the Late Quaternary lowstand and highstand deposits resting on rocky bedrock. A variety of fluid-escape features characterizes the area, including the Zannone giant pockmark, several smaller pockmarks, hummocky terrains and areas of positive relief. Ground-truth video data show active seepages, bacterial communities, widespread lithified pavements, mounds, and cone-shaped structures. Evidence of active seepage includes both continuous and intermittent bubble release from the seafloor and a well-defined plume rising 70 m above the seafloor.
The Zannone giant pockmark is about 900 × 500 m (surface of some 0.5 km2). It represents the first evidence of an active shallow-water seepage area in the central Tyrrhenian Sea (Italy) and the first record of a morphologically complex giant pockmark in the entire Mediterranean Sea.
Some speculations on processes originating the observed features are explored, including possible occurrence of multiple eruption events, processes of fluidization–liquefaction and minor slides that may have modified the original morphology. Factors peculiar to the study area – shallow depth, thin sedimentary cover resting on a faulted rocky basement, seeping occurring through non-cohesive sandy sediments appear to have been key to the formation and morphology of the Zannone giant pockmark
Attività sperimentale di rilievo dei fondali del fiume Tevere con metodologia Multibeam
No full textFluid emissions affecting lowstand shelf deposits on the flank of volcanic island (Zannone Island, Tyrrhenian sea, Italy).
No full textFluid emission affecting lowstand shelf deposits on the flank of a volcanic island (Zannone Island, Tyrrhenian Sea, Italy).
No full textSeveral Gas Related Features (GRFs) have been detected offshore the Western Pontine Archipelago by means of very high resolution multibeam bathymetry, high resolution seismic profiles, ROV video observations, water and sediment sampling.
Importance of GRFs is related to their association with hydrocarbon occurrence in the subsurface, settlement of endemic ecosystems and the possible direct or indirect linkage with marine geohazards (submarine slides, earthquakes, damage to seafloor infrastructures). In particular, at a broader spatial and temporal scale, geological emissions of methane may be take into consideration as geological factors controlling Quaternary atmospheric and climate changes.
Pontine Archipelago is located 30 kilometers from the Italian peninsula (Eastern Tyrrhenian Sea) and is composed of five Plio-Pleistocene volcanic islands: Ponza, Palmarola, Zannone (western sector) and Ventotene and S. Stefano (eastern sector). The research is focused on specific GRFs located offshore the eastern sector of Zannone Island, at water depth ranging between 105-130 m (outer continental shelf).
GRFs comprise: giant pockmark, several pockmarks and dome topographic features. The giant pockmark has elongated shape and is 900 m long and 500 m wide; pockmarks are characterized by circular, sub-circular and elongated shapes with dimensions ranging between 2-80 m; whereas dome topographic features are mostly cone-shaped structures with dimensions between 8-36 m.
ROV observations have revealed the occurrence of active fluid emissions escaping from the seafloor, characterized by different discharge modalities (continuous and intermittent) and presence of widespread bacterial mats, possible chemosynthetic bivalve aggregations, small scales cone structures and several burrows linked to bioturbation and/or fluid escaped. Moreover, water column backscatter data acquired by multibeam have revealed the occurrence of plumes extended to at least 70 m into the water column. Analysis of very high seismic profiles show the occurrence of several flares at the same location of plumes individuated by water column backscatter data and the occurrence of lowstand prograding deposits, covered by a few meters thick of Holocene deposits. Lowstand prograding deposits have a max thickness of about 35 m and across the giant pockmark show a chaotic seismic facies, indicating intense deformation.
To date, rare cases of active shallow-water cold seeps have been described in the Mediterranean Sea. Analysis of the morphological, sedimentological and stratigraphic characteristics of the study area provide the first evidence of an active shallow-water cold emission site in the Eastern Tyrrhenian Sea
Application of underwater acoustics to seafloor habitat mapping: examples from three case study (Hudson Canyon, Mississippi Canyon Block 118 and Pontine Insular Shelf)
No full textPrime evidenze di cold seeps attivi attraverso analisi integrata di dati geofisici (multibeam, backscatter, profili sismici) e dati di ground-truth nell'offshore dell'Isola di Zannone (Arcipelago Pontino Occ.)
No full text- …
