86,570 research outputs found
Slope fans and aprons dominated by supercritical bedforms: topographic and feeding system controls (Southeastern Tyrrhenian Sea)
No full textIn the marine environment, turbidite supercritical bedforms have been widely reported from channel-axis and overbank wedges. On the contrary, their dominance in the make-up of fans and apron, apart from local areas such as channel mouths, is at present not recognized. However, since it has been postulated that turbidity currents reach the supercritical conditions for slope > 0.5°, submarine slopes should contain abundant supercritical flow deposits. Here, we provide a review of different types of slope fans and aprons dominated by supercritical bedforms, based on examples from the modern seafloor. We compare depositional elements located in different intraslope basins of the Tyrrhenian Sea, through high-resolution bathymetry, chirp subbottom section and, where available cores. The variable geological context results in axial and transvers slope fans with highly variable sizes (few to tens of kilometres) and geometries, dependent upon the erosive and/or depositional processes involved, as well as the seafloor topography of the area. In particular, we have recognized two types of lobe-shaped deposits characterized by supercritical bedforms: channel-attached fans and detached aprons. The first ones are connected to a canyon-channel system and develop on slope gradients of 0.5° to 1.2°, display small-scale bedforms (wavelength of about 150 m and height < 10 m), with upslope asymmetric or symmetric cross-sections, interpreted as cyclic steps and antidunes. According to the amplitude of the reflections, cores, and to the bedform aspect ratio, the channel-attached fans are interpreted to be composed of coarse-grained sediments. Our examples highlight that cyclic steps and antidunes dominate the channel-attached fans both in axial and lateral portion while scours mark topographic changes such as breaks in slope or laterally confined areas. Detached aprons develop from the un-incised shelf edge on steep slopes of about 1.2° to 3° and are composed by large-scale bedforms (wavelength of about 500 m and height of about 5 m) mainly upslope asymmetric, associated with cyclic steps. The low amplitude of the seismic reflections suggests the fine-grained nature of the aprons. This study shows that there are significant differences in the distribution and character of supercritical bedforms in slope settings according to the type of feeding system, the degree of flow confinement and the seafloor topography. The analysis of the downslope evolution of turbidity currents, and of the character of associated bedforms in deep-water systems can contribute new perspectives to refine our models of deep-sea depositions
Perspectives of RDF use in Decentralized Areas: Comparing Power and Cogeneration Solutions
No full textPresent EU trends strive to maximize the resources recovery from municipal solid waste thus minimizing the waste amount to be disposed off. Refuse-derived fuel (RDF) production is considered in some countries to be a priority solution even if current market scenarios and consumers scepticism at present limit its widespread utilization. In this work, a comparison has been carried out of two possible RDF utilization alternatives, with particular reference to territorial districts with low population density. After a brief introduction, in which current RDF combustion technologies are illustrated, two possible plant configurations are considered, one concerning only electric power production; the other one combined heat and power production (CHP), using heat for district heating purposes, resorting to two different architectures: single pass-out condensing turbine and back-pressure turbine. Possible application of these technologies to a case study is then proposed, referring to a central Italy mountain territory characterized by a low population density. Then, an economic evaluation has been carried out. Finally, a parametric study was performed in order to define acceptable values for the sale price of thermal energy and the effect on profitability of the incremental investment needed for the construction of a district heating network
Downslope evolution of supercritical bedforms in a confined deep-sea fan lobe, Amantea Fan, Paola Basin (Southeastern Tyrrhenian Sea)
No full textThe sedimentology of upper flow regime bedforms represents an important research topic at the present. Deposits interpreted as those of supercritical flows are widely recognized in modern fan systems, but their recovery is challenging. Most of the sedimentological information has come from channel thalwegs but supercritical bedforms are also frequently downslope from the channel mouths. Such an environment has been identified in the Paola basin, where erosive and depositional cyclic steps have been imaged and identified in a sandy submarine lobe of the Amantea Fan. High-resolution sub-bottom profiles provide insight into the bedform internal architecture and their relationships with a frontally-confining ridge. For the first time, supercritical bedforms in a submarine lobe have been interpreted in two distinct positions: in the scour of an erosional cyclic step and in the stoss side of a depositional cyclic step. Coarse to medium-grained massive sand with flame structures, indicating rapid sediment fall-out and frequently associated with the occurrence of hydraulic jumps, has been identified in the scour and at the toe of the ridge. The latter represents an example of topographically induced hydraulic jumps driven by a frontal confinement. Top-cut-out medium to fine sands with tractive structures have been interpreted as the deposits related to the stoss side of a cyclic step or small-scale antidune superimposed on the cyclic step surface. The presented data broaden the understanding of the range of processes that are driven by the interaction between turbidity currents and seafloor topography and the dip of the slope. The recognition that topography influences the density structure and the degree of criticality of the flow and, consequently, the morphodynamics and facies of the relative deposits may help to explain sediment distribution and improve depositional models of fan lobes in confined settings
Perspectives of RDF use in Decentralized Areas: Comparing Power and Cogeneration Solutions
No full textPresent EU trends strive to maximize the resources recovery from municipal solid waste thus minimizing
the waste amount to be disposed off. Refuse-derived fuel (RDF) production is considered in some countries
to be a priority solution even if current market scenarios and consumers scepticism at present limit its
widespread utilization. In this work, a comparison has been carried out of two possible RDF utilization
alternatives, with particular reference to territorial districts with low population density. After a brief
introduction, in which current RDF combustion technologies are illustrated, two possible plant configurations
are considered, one concerning only electric power production; the other one combined heat and
power production (CHP), using heat for district heating purposes, resorting to two different architectures:
single pass-out condensing turbine and back-pressure turbine. Possible application of these technologies to
a case study is then proposed, referring to a central Italy mountain territory characterized by a low population
density. Then, an economic evaluation has been carried out. Finally, a parametric study was
performed in order to define acceptable values for the sale price of thermal energy and the effect on
profitability of the incremental investment needed for the construction of a district heating network
Downslope evolution of supercritical bedforms in a confined deep-sea fan lobe, Amantea Fan, Paola Basin (Southeastern Tyrrhenian Sea)
No full textThe sedimentology of upper flow regime bedforms represents an important research topic at the present. Deposits interpreted as those of supercritical flows are widely recognized in modern fan systems, but their recovery is challenging. Most of the sedimentological information has come from channel thalwegs but supercritical bedforms are also frequently downslope from the channel mouths. Such an environment has been identified in the Paola basin, where erosive and depositional cyclic steps have been imaged and identified in a sandy submarine lobe of the Amantea Fan. High-resolution sub-bottom profiles provide insight into the bedform internal architecture and their relationships with a frontally-confining ridge. For the first time, supercritical bedforms in a submarine lobe have been interpreted in two distinct positions: in the scour of an erosional cyclic step and in the stoss side of a depositional cyclic step. Coarse to medium-grained massive sand with flame structures, indicating rapid sediment fall-out and frequently associated with the occurrence of hydraulic jumps, has been identified in the scour and at the toe of the ridge. The latter represents an example of topographically induced hydraulic jumps driven by a frontal confinement. Top-cut-out medium to fine sands with tractive structures have been interpreted as the deposits related to the stoss side of a cyclic step or small-scale antidune superimposed on the cyclic step surface. The presented data broaden the understanding of the range of processes that are driven by the interaction between turbidity currents and seafloor topography and the dip of the slope. The recognition that topography influences the density structure and the degree of criticality of the flow and, consequently, the morphodynamics and facies of the relative deposits may help to explain sediment distribution and improve depositional models of fan lobes in confined settings
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