105 research outputs found
Very high resolution seismic surveys in the lagoon and gulf of Venice shallow waters
No full textWithin the framework of the geological mapping of the Venice area (CARG Project: Map Sheet 128 “Venezia” and Map Sheet 148-149 “Chioggia-Malamocco”) a very high resolution seismic survey (VHRS) was carried out to correlate data from hundreds of cores with the main aim to map the depth of the Late Pleistocene and Holocene unconformity (Brancolini et al., 2005; Rizzetto et al., 2005; Tosi et al., 2006a,b). Due to logistic and technical limits, the acquisition of seismic survey in the Venice Lagoon was restricted to the channels with more of 5 m water depth, most of them artificial or dredged. A new survey, with the aim to extend the VHRS surveys to the shallow water, such as the tidal flats, is in progress within the Co.Ri.La. Project framework (3.16 Subproject). The Co.Ri.La 3.16 Subproject is based on an acquisition system installed on a boat with a very shallow draught. The new survey will allow the detection and mapping of many interesting geological-geomorphologic structures, i.e. paleoriver beds, ancient lagoon channels and shoreline ridges, that are like-outcropping, and that have been only partially recognized in the previous surveys.PublishedBarcelona (Spain)7A. Geofisica di esplorazioneope
CONTRIBUTION OF SEISMIC PROFILES, HISTORICAL MAPS, AND DIGITAL ELEVATION MODEL TO DEFINE BURIED GEOMORPHOLOGICAL FEATURES IN THE VENICE LAGOON SUBSOIL (ITALY)
No full textRecently, the integrated analysis of Very High Resolution Seismic (VHRS) profiles, satellite images, aerial photographs, maps, and topographic/bathymetric data has given an important contribution to the identification of buried geomorphological features in the Venice lagoon subsoil down to about 30 m b.s.l.. Investigations allow to attribute these features to the Late Pleistocene and the Holocene and to point out their relation with the evolution of the lagoon basin.
Results of this study are also assuming great importance in relation to coastal environmental problems. Relict sandy geomorphological features, characterized by high permeability, act as preferred pathways for groundwater flow and solute transport, enhancing saltwater intrusion in the watershed (Carbognin & Tosi, 2003; Carbognin et al., 2005; Pousa et al., 2007). Furthermore, salinization process can also trigger land subsidence induced by clayey particles rearrangement (Meade, 1964).
In addition, the different kinds of deposits that characterize geomorphological features are responsible for a differential lowering of the territory (Teatini et al., 2005).
Aerial photograph and satellite image interpretations, analysis of historical and recent maps, field surveys, and topographic/bathymetric investigations were first used to identify the main buried and surface geomorphological features. Afterwards, an important contribution to the present study was given by a single channel VHR seismic system, optimized for surveys in shallow water less than 1 m depth (Brancolini et al., 2006; Brancolini et al., 2007).
Seismic profiles were calibrated and validated using geological information obtained from existing cores.
The detailed reconstruction of the seismic-morpho-stratigraphic units present in the subsoil of the Venice Lagoon is still in progress. It is obtained integrating results of the investigations previously described with sedimentological, stratigraphic, geotechnical, mineralogical, textural, and paleoenvironmental data, and 14C dating (Serandrei Barbero et al., 2006; Tosi et al., 2007a; Tosi et al., 2007b).
The combined interpretation of results obtained from remote sensing investigations, topographic/bathymetric measurements, VHRS surveys, and analysis of multidisciplinary geological data allowed the discovery and characterization of buried paleoriver beds, ancient tidal channels, and paleobeach ridges and pointed out the relation among geomorphological features occurring in the lagoon basin and in the watershed.
In fact, most of the features recognized in the mainland, which apparently come to an end in correspondence to the lagoon margin, continue into the lagoon basin, where their identification is made difficult by the presence of water and by depositional/erosive processes active in this kind of environment.
Data show that relict geomorphological features composed of high permeability deposits provide the hydraulic connection between freshwater aquifers and the sea. In particular, results of the present study point out that well developed paleoriver systems, intersecting the southern lagoon margin and the nearby coastline and characterized by permeable sediments, represent preferential way of communication among waters having different salinity. By contrast thick silty-clayey layers preclude the salty pollution in the aquifers from the lagoon and the sea.
As pointed out close to the lagoon margin (Rizzetto et al., 2003), the different kinds of deposits, related to the presence of distinct geomorphological features, contribute to the differential lowering of the lagoon basin (Teatini et al., 2005). In particular, organic soils correspond to highly sinking areas, whereas sandy-silty sediments, which constitute fluvial and beach ridges, are more stable.
Future investigations have to be addressed to the quantitative geomorphological analysis aimed to know the past hydrologic conditions of the drainage systems, and to analyze the formative processes that control the morphological setting and evolution of lowland fluvial river and tidal creek systems.PublishedMunich, Germany6A. Monitoraggio ambientale, sicurezza e territorioope
CONTRIBUTION OF SEISMIC PROFILES, HISTORICAL MAPS, AND DIGITAL ELEVATION MODEL TO DEFINE BURIED GEOMORPHOLOGICAL FEATURES IN THE VENICE LAGOON SUBSOIL (ITALY)
No full textRecently, the integrated analysis of Very High Resolution Seismic (VHRS) profiles, satellite images, aerial photographs, maps, and topographic/bathymetric data has given an important contribution to the identification of buried geomorphological features in the Venice lagoon subsoil down to about 30 m b.s.l.. Investigations allow to attribute these features to the Late Pleistocene and the Holocene and to point out their relation with the evolution of the lagoon basin.
Results of this study are also assuming great importance in relation to coastal environmental problems. Relict sandy geomorphological features, characterized by high permeability, act as preferred pathways for groundwater flow and solute transport, enhancing saltwater intrusion in the watershed (Carbognin & Tosi, 2003; Carbognin et al., 2005; Pousa et al., 2007). Furthermore, salinization process can also trigger land subsidence induced by clayey particles rearrangement (Meade, 1964).
In addition, the different kinds of deposits that characterize geomorphological features are responsible for a differential lowering of the territory (Teatini et al., 2005).
Aerial photograph and satellite image interpretations, analysis of historical and recent maps, field surveys, and topographic/bathymetric investigations were first used to identify the main buried and surface geomorphological features. Afterwards, an important contribution to the present study was given by a single channel VHR seismic system, optimized for surveys in shallow water less than 1 m depth (Brancolini et al., 2006; Brancolini et al., 2007).
Seismic profiles were calibrated and validated using geological information obtained from existing cores.
The detailed reconstruction of the seismic-morpho-stratigraphic units present in the subsoil of the Venice Lagoon is still in progress. It is obtained integrating results of the investigations previously described with sedimentological, stratigraphic, geotechnical, mineralogical, textural, and paleoenvironmental data, and 14C dating (Serandrei Barbero et al., 2006; Tosi et al., 2007a; Tosi et al., 2007b).
The combined interpretation of results obtained from remote sensing investigations, topographic/bathymetric measurements, VHRS surveys, and analysis of multidisciplinary geological data allowed the discovery and characterization of buried paleoriver beds, ancient tidal channels, and paleobeach ridges and pointed out the relation among geomorphological features occurring in the lagoon basin and in the watershed.
In fact, most of the features recognized in the mainland, which apparently come to an end in correspondence to the lagoon margin, continue into the lagoon basin, where their identification is made difficult by the presence of water and by depositional/erosive processes active in this kind of environment.
Data show that relict geomorphological features composed of high permeability deposits provide the hydraulic connection between freshwater aquifers and the sea. In particular, results of the present study point out that well developed paleoriver systems, intersecting the southern lagoon margin and the nearby coastline and characterized by permeable sediments, represent preferential way of communication among waters having different salinity. By contrast thick silty-clayey layers preclude the salty pollution in the aquifers from the lagoon and the sea.
As pointed out close to the lagoon margin (Rizzetto et al., 2003), the different kinds of deposits, related to the presence of distinct geomorphological features, contribute to the differential lowering of the lagoon basin (Teatini et al., 2005). In particular, organic soils correspond to highly sinking areas, whereas sandy-silty sediments, which constitute fluvial and beach ridges, are more stable.
Future investigations have to be addressed to the quantitative geomorphological analysis aimed to know the past hydrologic conditions of the drainage systems, and to analyze the formative processes that control the morphological setting and evolution of lowland fluvial river and tidal creek systems.PublishedMunich, Germany6A. Monitoraggio ambientale, sicurezza e territorioope
Very high resolution seismic surveys in the lagoon and gulf of Venice shallow waters
No full textWithin the framework of the geological mapping of the Venice area (CARG Project: Map Sheet 128 “Venezia” and Map Sheet 148-149 “Chioggia-Malamocco”) a very high resolution seismic survey (VHRS) was carried out to correlate data from hundreds of cores with the main aim to map the depth of the Late Pleistocene and Holocene unconformity (Brancolini et al., 2005; Rizzetto et al., 2005; Tosi et al., 2006a,b). Due to logistic and technical limits, the acquisition of seismic survey in the Venice Lagoon was restricted to the channels with more of 5 m water depth, most of them artificial or dredged. A new survey, with the aim to extend the VHRS surveys to the shallow water, such as the tidal flats, is in progress within the Co.Ri.La. Project framework (3.16 Subproject). The Co.Ri.La 3.16 Subproject is based on an acquisition system installed on a boat with a very shallow draught. The new survey will allow the detection and mapping of many interesting geological-geomorphologic structures, i.e. paleoriver beds, ancient lagoon channels and shoreline ridges, that are like-outcropping, and that have been only partially recognized in the previous surveys.PublishedBarcelona (Spain)7A. Geofisica di esplorazioneope
Bathymetric map of Lago Fagnano (Tierra del Fuego Island)
No full textWe present a general bathymetric map of Lago Fagnano, the largest ice-free lake of the Southern Hemisphere, located in the central part of the Tierra del Fuego Island. The map has been obtained compiling all the available bathymetric soundings and depth-converted high-resolution seismic profiles, collected in the course of several geophysical campaigns. The lake occupies a 110-km long, E-W trending tectonic depression within the southernmost tip of the Andean Cordillera, where the South America-Scotia plate boundary traverses the Tierra del Fuego Island. The map allows us to identify the main morpho-bathymetric features of Lago Fagnano. The lake floor is divided into two principal sectors of different water depths, separated by a main shoal located in the central part of the lake. Maximum water depth (206 m) is found in the eastern part, whereas water depths in the western half do not exceed 165 m. In this paper, we describe the geometry and the general morphological characteristics of the basin, which was generated by a combination of distinct tectonic processes, and later superposed by Late Quaternary glacial and glacio-lacustrine dynamic events.Fil: Zanolla, C.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Lodolo, E.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale ; ItaliaFil: Lippai, Horacio Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Instituto de Geofísica "Daniel Valencio"; ArgentinaFil: Tassone, Alejandro Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Instituto de Geofísica "Daniel Valencio"; ArgentinaFil: Menichetti, M.. Università di Urbino; ItaliaFil: Baradello, L.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Grossi, H. L.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Hormaechea, Jose Luis. Estación Astronomica de Río Grande; Argentin
Understanding the hydrogeology of the Venice Lagoon subsurface with airborne electromagnetics
No full textThe occurrence of alternating dry/wet conditions in transitional environments, such as wetlands, deltas, and lagoons, usually challenges the use of traditional direct and geophysical surveys for comprehensive hydrogeologic investigations. Moreover, significant mixing between continental fresh groundwater and marine salty surface waters generally takes place in these flat coastal areas. Airborne electromagnetics (AEM) is a promising tool in this respect, as it provides, in a fast and cost effective manner, large-scale distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models. The results of a SkyTEM AEM survey in the Venice Lagoon, Italy, show the capability of this technique to significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland subsurface, irrespective of the different features characterizing the area. The environment consists of salt marshes, mud flats, shallows, tidal channels, islands, together with reclaimed farmlands crossed by natural watercourses and drainage channel networks. In particular, the AEM shows (i) the presence of fresh water (with resistivity larger than 20 Ohm m) underneath the central part of the lagoon at depths from 10 to 25 m below m.s.l., (ii) the interface between different relevant stratigraphic units, e.g., the clayey layer bounding the Holocene–Pleistocene sedimentation, and (iii) the occurrence of areas with possible submarine fresh groundwater discharge. Moreover, the source and inland extent of the saltwater contamination in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed. AEM data were complemented with very high resolution seismic (VHRS) acquisitions. The integrated
analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability of the subsurface fluids
The subsoil architecture of the Lagoon and Gulf of Venice (Italy) by very high resolution seismic surveys in shallows
No full textThe Project “Application of innovative of very high resolution seismic methodologies in shallow waters aimed at the study of the subsoil of the Venice Lagoon” allowed the characterization of the Late Pleistocene and Holocene depositional sequences with a detail, that has never been reached in the past.
A boat, particularly suitable for very high resolution seismic survey in shallow water (less than 1 m deep) has been fully equipped and tested. It allowed to carried out surveys of specific areas of the Lagoon that have never been investigated in the past. Moreover a seismo-stratigraphic model of the lagoon and gulf of Venice subsoil has been performed. The seismic acquisition system allowed to investigate the subsoil down to 30-40 m deep.
The new data provided significant geological features related to the Late Pleistocene and Holocene evolution of the investigated areas: the southern lagoon, the Lido and Chioggia inlets and part of the shelf of the Gulf of Venice.PublishedVenice, Italy7A. Geofisica di esplorazioneope
Understanding the hydrogeology of the Venice Lagoon subsurface with airborne electromagnetics
No full textThe occurrence of alternating dry/wet conditions in transitional environments, such as wetlands, deltas, and lagoons, usually challenges the use of traditional direct and geophysical surveys for comprehensive hydrogeologic investigations. Moreover, significant mixing between continental fresh groundwater and marine salty surface waters generally takes place in these flat coastal areas. Airborne electromagnetics (AEM) is a promising tool in this respect, as it provides, in a fast and cost effective manner, large-scale distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models. The results of a SkyTEM AEM survey in the Venice Lagoon, Italy, show the capability of this technique to significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland subsurface, irrespective of the different features characterizing the area. The environment consists of salt marshes, mud flats, shallows, tidal channels, islands, together with reclaimed farmlands crossed by natural watercourses and drainage channel networks. In particular, the AEM shows (i) the presence of fresh water (with resistivity larger than 20 Ω m) underneath the central part of the lagoon at depths from 10 to 25. m below m.s.l., (ii) the interface between different relevant stratigraphic units, e.g., the clayey layer bounding the Holocene-Pleistocene sedimentation, and (iii) the occurrence of areas with possible submarine fresh groundwater discharge. Moreover, the source and inland extent of the saltwater contamination in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed. AEM data were complemented with very high resolution seismic (VHRS) acquisitions. The integrated analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability of the subsurface fluids. © 2011 Elsevier B.V
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