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Early Cretaceous tectonic event in the Adria: Insight from Umbria-Marche pelagic basin (Italy)
No full textSoft-sediment deformation structures crop out in the Lower Cretaceous succession of the Gubbio anticline in the Umbria-Marche Apennines of Italy. The deformation interval is ~13 m thick and occurs between the upper Hauterivian–lower Aptian Maiolica Formation and the Aptian Marne a Fucoidi Formation. It can be observed along the anticline for a distance of 12 km.
Different types of deformation structures are distributed in several outcrops, with detachment extensional structures prevailing in the southeast sector. Imbricated slides, slump structures, and chaotic layers are distributed vertically and longitudinally in the middle and/or lower part of the deformed sediments. In the northwest sector of the anticline, compressional duplex structures can be considered the lower section of a large sediment failure. Geometrical and kinematic analysis of the fold axis trends and sliding surfaces have led to infer a single, large gravitational event possibly Albian in age. The synsedimentary deformation could be activated by several internal trigger
mechanisms induced by external regional tectonic events such as earthquakes. An orthogonal system of calcite veins crossing the limestone layers represents the primary pathway for fl uid-driven breaching of joint seals. These fl uids can be related to the significant increase in the total organic carbon in the Hauterivian–Aptian layer of the Maiolica and Marne a Fucoidi Formations. This suggests the possibility that the limestone layer, sandwiched and sealed between clay of the organic-rich black shales, could have favored a pore pressure increase approaching lithostatic stress. With a thin overburden, lithostatic stress is more easily reached at low hydrostatic pressure. This slump sheet occurrence suggests the existence of a local paleoslope dipping toward the north-northwest, where the mass involved in the deformation is distributed over an estimated area of 60 km2 for a volume of 0.8 km3 of displaced sediments.
The restoration and rotation of the slump fold hinges to the Early Cretaceous direction, in line with available paleomagnetic data, have shown that the strike of the slope corresponds to the main trend of the oldest Jurassic extensional lineaments and is linked to transform faults of the westernmost Tethys rifting systems
CO2 and speleogenesis: suggestions from hypogene karst of Italy
Full text linkThe CO2 driving the main karst processes needs to be considerate from different sources. The carbon dioxide produced in the soil and dissolved in the percolation water is considered as the main agent for karstification in the carbonate rocks. Superficial morphologies and underground caves are product of the corrosion of the limestone, while carbonate speleothems is the other end member of the process. Hypogene speleogenesis driven by deep seated fluids is the cave formation processes for the main karst systems in the Apennines of Italy. Hydrogen sulfide and endogenic carbon dioxide are the main agents for underground karst corrosion and the soil carbon dioxide plays a secondary rule. The limestone corrosion driven by hydrogen sulfide produces gypsum deposits in caves that could be assumed as the indicator of the hypogene speleogenesis. The action of endogenic carbon dioxide in the cave formation, especially if it operates at lower temperature, is not easy to detect and the resulting cave morphology is not helpful to recognize the cave formation process. The main sources of carbon dioxide in the underground karst system in the Apennines of Italy can be related to different processes driven by the endogenic fluids emissions. The crustal regional degassing seems to be the prevalent source for carbon dioxide in the karst massifs with the main release in the groundwater. Hydrogen sulfide and methane oxidation, possibly mediated by bacteria activity, are other sources in the buried Cenozoic sediments. Releasing of carbon dioxide along the faults and in the fractures occurring in the carbonate rocks is an important source, especially in theseismically active area. Finally, thermogenic reactions with carbonate rocks are well known as one of the main production mechanism of carbon dioxide released in the atmosphere. Data from carbon dioxide monitoring in several caves show a relevant contribution of the endogenic carbon dioxide (about 75 %) in the karst system which drives the speleogenesis reactions and shapes the underground morphologies
HYPOGENIC CAVES IN WESTERN UMBRIA(CENTRAL ITALY)
Full text linkThree karst areas located in the western sector of the Umbria Region (Central Italy) are here described: one northof Perugia, and the others to the south, close to Todi. All the end members of karst processes, from solution caves to Quaternary travertine deposits, are present in this region, associated withCO2 and H2S emissions. The geological and hydrogeological aspects of the main karst systems are analyzed and their underground morphologies and patterns taken into account. Caves have different sizes and vary from a single conduit to complex systems, where the passages show features related to a possible hypogenic speleogenesis. In the area northof Perugia there are small horizontal and vertical solution caves developed in poorly karstified marly limestone, along fracture systems, where phreatic morphologies are prevalent. The endogenic CO2 emissions seem to drive the underground karst evolution. Pozzi della Piana, located west of the town of Todi, is a fossil branchform network cave system developed in a Quaternary travertine and extending for more than 2500 m. The cave passages are arranged on at least two levels, withphreatic morphologies, cupola ceilings, and blind pits. Microcrystalline spalled gypsum blocks are associated withcusp features and wall pockets. The cave-forming process is believed to be linked to travertine deposition by supersaturated carbonate hydrothermal water richin H2S. In the Parrano area, the underground karst system consists of solution caves extending for many hundreds of meters at different elevations in bothsides of a small gorge. The cave patterns vary from single conduits to ramiform passages withanastomotic galleries and pits that intercept the water table witha temperature of 26°C, p CO2 of 10-1 atm, and H2S concentrations of 10 mg/l. Spongework, corrosion pockets, and cupola ceilings are common morphologies, withgypsum replacing limestone wall deposits. Cave formation by hypogenic speleo genesis is also well known in the Apennine karst system of M. Cucco and Frasassi, where bothfossil and active processes are observable. The same processes are responsible for the genesis of these karst systems in different geological and hydrogeological contexts.
Structural setting of the Acquasanta Terme geothermal system (Ascoli Piceno)
Full text linkThe low temperature (<50°) geothermal field of Acquasanta is located in a carbonate reservoir in the core of an anticline surronded by marls and sandstones acquiclude. The thermal water rises along an extended fracture system related to strike-slip faults. Thermal and geochemical dilutions occur in the upper part of the water-table. The water temperatures recorded in a deep karst system, show a predominant convective heat transfer along the fractures and a conductive thermal flow in the rock matrix. The hydrogeological system can be related to a thermally driven convective circulation, with a regional recharged area located in the Sibillini Mountains, a flow few kilometres depth, and a discharge along the F. Tronto valley
Hydrostructural characterization of the karst reservoir in the Umbria-Marche Apennine, Italy
No full textIn carbonate reservoir, the flow patterns are conditioned by the degree of karsification of the main conduit networks and by the lower permeability microfractured blocks. To quantify patterns and nature of discontinuities in the rock mass is the main goal in the fluid circulation researches. Indeed fractures such as joint and bedding planes control infiltration, percolation and migration of groundwater into a reservoir. In the Umbria-Marche Apennine the Lower Jurassic limestones represents the basal reservoir where the larger hydrogeological structures are locate. The stratigraphic and structural setting forces a parallel-to-the ridge circulation of groundwaters, and the ridge itself can be considered as an isolated hydrogeological system. A quantitative fractures analysis was been considerate through the whole anticline, from the gently deep SW limb, in the weakly deformed hinge zone to the subvertical and much more deformed NE external side. The prevalent joint systems are oriented N55 and N295, located in the fold limbs and in the hinge zone. Besides, N15 and N345 joint systems are predominant only in western and eastern limbs of the anticline. In the hinge zone the fractures seem to be linked to a normal faults oriented at NW and SE, in correspondence of the crestal area; possibly these shear structures are responsible both for new systems development and for pre-existent sets partial reorientation. Dip discontinuities distribution gave remarkable about water process once infiltration inside the system. The high dips strongly contributed to increase groundwater percolation velocity coming both from direct infiltration areas in the upper hydrogeological complexes. Finally, spacing and frequency fracturation analysis identify rock mass properties from a quantitative point of view; these structural parameters allowed to obtained important considerations about both mechanical and hydrogeological features of a reservoir. The Giordano karst spring drains the SW limb of the M. Nerone anticline with an average discharge of more than 0,1 m3/sec and with a catchment area of about 4 km2. A deterministic approach for the hydrostructural characterization of the spring was adopted using discharge, temperature and water conductivity. The analysis of the hydrographs show that the base flow represent only the 30% and in the recession curve the discharge is controlled by the karst conduits drainage. The recession curves show different steps with a depletion constant of about 10-3 day-1, while the water temperature and electrical conductivity show variations where prevails the conduits drainage respect the fractured matrix. The complex variability and heterogeneity of the karst reservoir seems to be controlled by the larger karst conduits, which are related to the main fracture patterns
Heat as a tool for hydrodynamic characterization of fractured karst systems in Italy’s Northern Apennines
Full text linkCarbonate aquifers represent the main reservoir in the Apennines. The degree of their karstification controls the heterogeneity and anisotropy of the system at different scales. Bulk permeability of the karstified rock mass is controlled by a dual behavior, in which one end member is the conduit network with high hydraulic conductivity and short water-residence time, and the other is the microfractured blocks with longer water-residence times.
The geometry and the location of these flow paths in the study area are poorly constrained. An analysis of hydrographs integrated with the chemical or thermal responses can provide useful information on the geometries of the conduit drainages. A comparison of the thermal response of the karst springs with the record of cave stream temperatures will allow to distinguish between the conduit drainage and that of the fracture network. The spring hydrograph response is mainly controlled by the geometry of karst conduits and by the variation of the recharge area. Convective heat exchange in the channels and non-conservative thermal exchange between the water and the porous matrix characterize the flow in the whole karst system, as recorded by the heat output signals. The temperature signal in the conduits tends to be augmented by the high flow velocities, while being dampened by heat conduction resulting from the low flow velocities in fracture matrix. Using this information, the relationship between the system geometry and recharge area can be better defined.
The Scirca Spring is located at the foot of the Monte Cucco karstic massif in Italy’s Northern Apennines, where outcrops of Meso-Cenozoic carbonates are observable. The average discharge of the spring is about 0.2 m3/sec. It has a catchment area of about 3.4 km2 characterized by 30 km of karst conduits extending to a depth of about 1km. Several caves, in which underground streams feed the phreatic zone, allow to access the vadose zone of the drainage system. The karst aquifer was characterized by comparing the thermal behavior of the spring with that of the different cave streams as well as with the tracer test results and other physical-chemical data. The thermographs indicate a minimum of three fluctuation patterns, with hourly, daily and seasonal. The seasonal variations are out of phase with respect to the surface temperatures, showing a lag of many months. This data suggest a dampening effect exerted by the phreatic zone, in which the fracture network controls the main drainage and local inputs can modify the short term temperature signal
GEOSUR2004: Mesozoic to Quaternary evolution of Tierra del Fuego and neighboring austral regions I
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