Search results for "Geomorphology"
showing 10 items of 395 documents
Comment on "Displacement along the Karakoram fault, NW Himalaya, estimated from LA-ICP-MS U Pb dating of offset geologic markers" published by Shifen…
2013
International audience; Field evidence for syn-deformation migmatization and crystallization along the Karakorum fault contradicts the study of Wang et al. (2012). The ages of such magmatic rocks provide minimum ages for the onset of deformation at similar to 23 Ma in North Ayilari and similar to 19 Ma in Tangtse. The onset of deformation at 12 Ma in the Ayilari range inferred by Wang et al. (2012) from a muscovite Ar/Ar age is a cooling age, thus only a minimum age. The similar to 60 Ma granodiorite bodies, the ophiolitic rocks and the south Kailash thrust that are correlated across the fault to provide a 52 +/- 2 km finite offset do not define reliable piercing points. Such observations a…
Selection of the Optimal Design Rainfall Return Period of Urban Drainage Systems
2014
Abstract The aim of this work is to define a methodology to identify the optimal rainfall return period for the design of urban drainage systems. The choice of the optimal return period is made minimizing the total costs of the system: the sewer network is dimensioned for a set of possible design rainfall return periods, and the corresponding construction, maintenance and operation costs are evaluated. For each scenario, the total expected damage from flooding caused by rainfall events with return period greater than the design one is then estimated by hydraulic simulation. This methodology has been applied to a small urban catchment in Palermo (Italy).
Two-dimensional apparent microfabric of the basal Late Weichselian till and associated shear zone: case study from western Latvia
2008
The examination of glacial sediments in thin sections has become a common procedure in recent years. Apparent sand grain orientation (microfabric) in thin sections is one of the key elements marking certain microstructures. In an attempt to make till micromorphology studies less subjective and investigate the orientation of sand-sized particles in tills, we have developed an image analysis procedure to measure and analyse the spatial distribution of the till microfabric. We studied 13 thin sections of the Weichselian subglacial till and basal shear zone outcropping in the Baltic Sea bluffs at the Ziemupe site in western Latvia. The results were visualized as a two-dimensional grid of rose d…
Identifying sedimentary structures and spatial distribution of tsunami deposits with GPR - examples from Spain and Greece
2011
Shallow drilling in coastal areas like southern Spain and different parts of Greece (Corinth region and Argolis Gulf) proved evidence for tsunamis. Sedimentary analyses were conducted to identify tsunamigenic deposits, but did not reveal sedimentary structures or spatial distribution of tsunamites in a regional scale. Since drilling is time-intensive and expensive (depending on extend), this method can by far not cover an entire coastal area. On the other hand, distribution and preservation of tsunamigenic deposits seems to be highly variable. We used ground penetrating radar (GPR) in combination with electrical resistivity tomography (ERT) measurements and sedimentological research methods…
Marqueurs d'une structuration extensive jurassique en arrière de la marge nord-téthysienne (monts du Mâconnais, Bourgogne, France)
2000
Structural analysis of extensional faults in the Mâconnais Hills shows that low-intensity extensional phenomena occurred back from the passive margin of the Ligurian Tethys, the axis of which lay some 400 km southeast of the study area in Mid-Jurassic times. Storm-induced rip current directions and coral lens positions suggest that the palaeotopography was maintained by early faulting.
Structural framework and crustal characteristics of the Sardinia Channel Alpine transect in the central Mediterranean
2000
Abstract The submerged area located between the Sardinia Channel and the western Sicily offshore has been investigated based on deep crustal and conventional seismic lines with the aim of illustrating the relationships between the crust and its overlying crystalline and sedimentary thrust wedge. Analyses of seismic attributes and reflector pattern, supported by dredge hauls, also provided data in areas where stratigraphic and lithologic control is absent. Crustal geometries, tectonic processes and timing of the deformation are discussed here. North of the Elimi chain (central Sardinia Channel) the reflecting body consists of superposed tectonic wedges of crystalline rocks and their Meso-Cen…
High-pressure metamorphism in the Aegean, eastern Mediterranean: Underplating and exhumation from the Late Cretaceous until the Miocene to Recent abo…
2003
[1] We report 40Ar/39Ar ages from various tectonic units in the Aegean and westernmost Turkey. On the basis of published geochronologic data and our 40Ar/39Ar ages we propose that the Aegean is made up of several high-pressure units, which were successively underplated from the Late Cretaceous until the Miocene. Ages for high-pressure metamorphism range from 80–83 Ma in parts of the Vardar-Izmir-Ankara suture zone in the north to 21–24 Ma for the Basal unit in the Cyclades and the external high-pressure belt on Crete in the south. Published seismic data suggest that high-pressure metamorphism is currently occurring underneath Crete. Younging of high-pressure metamorphism in a southerly dire…
Historical mining and smelting in the Vosges Mountains (France) recorded in two ombrotrophic peat bogs
2010
Two peat sequences were sampled in the vicinity of the main mining districts of the Vosges Mountains: Sainte-Marie-aux-Mines and Plancher-les-Mines. Lead isotopic compositions and excess lead fluxes were calculated for each of these radiocarbon-dated sequences. Geochemical records are in very good agreement with the mining history of the area, well known over the last millennium. Except for an anomaly corresponding to the Middle Bronze Age which has not yet been resolved, there is no clear geochemical evidence of local metal production in the Vosges before the 10th century as excess lead deposition archived between 500 BC and 500 AD is attributed to long-range transport of polluted particul…
Coseismic geochemical variations in some gas emissions of Umbria region (Central Italy)
2000
Abstract Coseismic geochemical variations have been detected in some gaseous vents and natural springs during the last seismic crisis occurred in Umbria region (Central Apennines), that started on September 26th, 1997 with several moderate earthquakes (up to M1 5.8). The results of chemical analyses performed on both gas and water samples taken at a weekly rate, combined with analyses on continuous gas flow rate nearby San Faustino site, suggest that the variations can be interpreted as possible consequence of the crustal permeability changes induced by earthquake shaking.
The Nahe Caldera — A resurgent Caldera in the permocarboniferous Saar Nahe basin, SW-Germany
1984
In the Saar Nahe basin, SW-Germany, a large resurgent caldera complex of Lower Permian age was recognized recently, for which the name „Nahe Caldera” is proposed.