The potential of point clouds for the analysis of rock kinematics in large slope instabilities: examples from the Swiss Alps: Brinzauls,Pizzo Cengalo and Spitze Stei     

Kenner  Robert  Gischig  Valentin  Gojcic  Zan  Qu&#;au  Yvain  Kienholz  Christian  Figi  Daniel  Th&#;ny  Reto  Bonanomi  Yves 《Landslides》2022,19(6):1357-1377

Landslides - Lidar measurements and UAV photogrammetry provide high-resolution point clouds well suited for the investigation of slope deformations. Today, however, the information contained in...  相似文献   

Segmental closure of the Mongol-Okhotsk Ocean: Insight from detrital geochronology in the East Transbaikalia Basin     

Anastasia V.Arzhannikova  Elena I.Demonterova  Marc Jolivet  Ekaterina A.Mikheeva  Alexei V.Ivanov  Sergey G.Arzhannikov  Valentin B.Khubanov  Vadim S.Kamenetsky 《地学前缘(英文版)》2022,13(1):101254

The Late Paleozoic–Early Mesozoic Mongol-Okhotsk Ocean extended between the Siberian and Amur–North China continents.The timing and modalities of the oceanic closure are widely discussed.It is largely accepted that the ocean closed in a scissor-like manner from southwest to northeast(in modern coordinates),though the timing of this process remains uncertain.Recent studies have shown that both western(West Transbaikalia)and eastern(Dzhagda)parts of the ocean closed almost simultaneously at the Early–Middle Jurassic boundary.However,little information on the key central part of the oceanic suture zone is available.We performed U-Pb(LA-ICP-MS)dating of detrital zircon from wellcharacterized stratigraphic sections of the central part of the Mongol-Okhotsk suture zone.These include the initial marine and final continental sequences of the East Transbaikalia Basin,deposited on the northern Argun-Idemeg terrane basement.We provide new stratigraphic ages for the marine and continental deposits.This revised chronostratigraphy allows assigning an age of~165–155 Ma,to the collisionrelated flexure of the northern Argun-Idemeg terrane and the development of a peripheral foreland basin.This collisional process took place 5 to10 million years later than in the western and eastern parts of the ocean.We demonstrate that the northern Argun-Idemeg terrane was the last block to collide with the Siberian continent,challenging the widely supported scissor-like model of closure of the MongolOkhotsk Ocean.Different segments of the ocean closed independently,depending on the initial shape of the paleo continental margins.  相似文献   

Multi-criteria spatialization of soil organic carbon sequestration potential from agricultural intensification in Senegal     

Valentin Bellassen  Raphaël J. Manlay  Jean-Pierre Chéry  Vincent Gitz  Assize Touré  Martial Bernoux  Jean-Luc Chotte 《Climatic change》2010,98(1-2):213-243

On the eve of the 15th climate negotiations conference in Copenhagen, the pressure to assess all climate mitigation options is mounting. In this study, a bio-physic model and a socio-economic model were designed and coupled to assess the carbon sequestration potential of agricultural intensification in Senegal. The biophysical model is a multiple linear regression, calibrated and tested on a dataset of long-term agricultural trials established in West Africa. The socio-economic model integrates both financial and environmental costs related to considered practice changes. Both models are spatially explicit and the resulting spatial patterns were computed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65–0.83 MtC. With regards to local-scaled intensification as local projects, the most profitable areas were identified in agricultural expansion regions (especially Casamance), while the areas that meet the current financial additionality criteria of the Clean Development Mechanism were located in the northern part of the Peanut Basin. Using the current relevant mode of carbon valuation (Certified Emission Reductions), environmental benefits are small compared to financial benefits. This picture is radically changed if “avoided deforestation”, a likely consequence of agricultural intensification, is accounted for as the greenhouse gases sink capacity of projects increases by an average of a hundred-fold over Senegal.  相似文献   

Formation of caldera periphery faults: an experimental study     

Thomas R. Walter  Valentin R. Troll 《Bulletin of Volcanology》2001,63(2-3):191-203

Changing stresses in multi-stage caldera volcanoes were simulated in scaled analogue experiments aiming to reconstruct the mechanism(s) associated with caldera formation and the corresponding zones of structural weakness. We evaluate characteristic structures resulting from doming (chamber inflation), evacuation collapse (chamber deflation) and cyclic resurgence (inflation and deflation), and we analyse the consequential fault patterns and their statistical relationship to morphology and geometry. Doming results in radial fractures and subordinate concentric reverse faults which propagate divergently from the chamber upwards with increasing dilation. The structural dome so produced is characterised bysteepening in the periphery, whereas the broadening apex subsides. Pure evacuation causes the chamber roof to collapse along adjacent bell-shaped reverse faults. The distribution of concentric faults is influenced by the initial edifice morphology; steep and irregular initial flanks result in a tilted or chaotic caldera floor. The third set of experiments focused on the structural interaction of cyclic inflation and subsequent moderate deflation. Following doming, caldera subsidence produces concentric faults that characteristically crosscut radial cracks of the dome. The flanks of the edifice relax, resulting in discontinuous circumferential faults that outline a structural network of radial and concentric faults; the latter form locally uplifted and tiltedwedges (half-grabens) that grade into horst-and-graben structures. This superimposed fault pattern also extends inside the caldera. We suggest that major pressure deviations in magma chamber(s) are reflected in the fault arrangement dissecting the volcanoflanks and may be used as a first-order indication of the processes and mechanisms involved in caldera formation.  相似文献   

Pre-eruptive magma mixing in ash-flow deposits of the Tertiary Rum Igneous Centre,Scotland     

Valentin?R.?TrollEmail author  Colin?H.?Donaldson  C.?Henry.?Emeleus 《Contributions to Mineralogy and Petrology》2004,147(6):722-739

The Northern Marginal Zone of the Rum Igneous Centre is a remnant of an early caldera and its infill. It is composed of intra-caldera breccias and various small-volume pyroclastic deposits, overlain by prominent rhyodacite ash-flow sheets of up to 100 m thickness. The ash-flows were fed from a feeder system near the caldera ring-fault, and intrusive rhyodacite can locally be seen grading into extrusive deposits. A variety of features suggest that the ash-flows were erupted from a magma chamber that contemporaneously hosted felsic and mafic magmas: (i) chilled basaltic inclusions in rhyodacite; (ii) formerly glassy basaltic to andesitic enclaves with fluid-fluid relationships; (iii) feldspars with thick reaction rims enclosed in the basaltic to andesitic inclusions, yet with cores chemically resembling those of the rhyodacite: (iv) trace element compositions of the rhyodacite and the mafic enclaves form a mixing line between the end-member rhyodacite and basalt compositions. Additionally, textural and chemical features in the rhyodacite feldspar phenocrysts are consistent with magma mixing; (v) feldspars with resorption embayments cutting through internal zonation of the crystals; (vi) complexly zoned crystals with sieve-textured zones that are overgrown with euhedral zones; (vii) oscillatory zonation of feldspar phenocrysts in the rhyodacite, showing sharp increases in anorthite (An 10%) followed by gradual decrease in An-content (An 4%). This evidence points to eruption of ash-flows from a felsic magma chamber that was periodically replenished by injection of mafic magma. Diffusional mixing between the two magmas was permitted by temperature and compositional differences, but was slow due to the contrast in viscosities and densities. The Fe–Ti–P-enriched basic magma that replenished the chamber was degassing on entering the lower temperature environment and soon equilibrated thermally, followed by chemical exchange between the two end-member magmas. This process formed hybrid andesite enclaves enriched in trace elements beyond that caused by simple mixing, implying trace element diffusion in addition to bulk mixing. Eruption was caused by replenishment with, and degassing of, the basic magma and the chamber partially evacuated while the process of hybridisation was underway. The erupted products record magma mixing by chamber replenishment, blending of two magmas and elemental exchange in the magma chamber, and also physical mingling in the eruptive conduit.  相似文献   

Proposal for selection of control,preventive and rehabilitation measures based on degradation land level and geoindicators in the fortaleza metropolitan region,State of Ceará, Brazil     

Lázaro Valentin Zuquette  Jaime Quintas dos Santos Collares  Osni José Pejon 《Environmental Geology》2007,52(5):899-922

Preventive, controlling, rehabilitative and corrective measures to improve the environmental quality of the hydrographic basins of the Fortaleza metropolitan region in the state of Ceará (Brazil) are presented based on geological and geotechnical data, land degradation rates and sources, and other geoindicators. The region is affected by coastal and stream erosion, gravitational mass movement, dunes, silting, and water pollution, sanitary landfills in inappropriate sites, decommissioned and abandoned aggregate mining, and swamp areas. Geoindicators were used to classify each of the 12 hydrographic basins as possessing low (4), intermediate (3), or high (5) degradation levels. A group of 59 environmental management measures related to ecological, bioengineering, mechanical, policy and administrative, agricultural and clean-up methods was selected. From this general group a set of 31 measures was chosen considering goals, efficacy for specific environmental problems, suitability for large or small areas, behavior under different annual climatic conditions, environmental problems of the region, geological and geotechnical limitations and degradation level of the basins. A set of the more suitable geoindicators was selected for monitoring efficiency of the measures for each basin.  相似文献   

Cenomanian florule of Nammoura, Lebanon     

Valentin Krassilov  Flavio Bacchia 《Cretaceous Research》2000,21(6):785

The mid-Cenomanian fish beds of Nammoura, Mont-Liban district, Lebanon contain a diverse fauna of aquatic and terrestrial vertebrates, a few crustaceans and moderately well-preserved plant remains of which a single species,Sapindopsis anhouryi , was previously described by Dilcher & Basson (1990). We add 11 species of ferns, gymnosperms and angiosperms of which Nammouria cretacea gen. et sp. nov, Nupharanthus cretacea gen. et sp. nov., Sapindopsis libanensis sp. nov. and Nammourophyllum altingioides gen. et sp. nov. are new taxa. The florule differs markedly from both Early Cretaceous and Turonian plant assemblages of the Middle East, thereby representing a distinct stage of the regional floristic evolution. Its phytogeographic affinities are with contemporaneous floras of North America, Central Europe and the Crimea. A combination of such features as xeromorphism, the prevalence of compound leaves, and the presence of deciduous angiosperm components and gymnosperms may indicate climatic conditions similar to those of the present day Mediterranean.  相似文献   

New Albian macro- and palynoflora from the Negev (Israel) with description of a new gymnosperm morphotaxon     

Valentin Krassilov  Eckart Schrank 《Cretaceous Research》2011,32(1):13-29

New plant macrofossil localities are found in the middle-upper part of the Albian Upper Hatira Formation of Makhtesh Qatan, an erosion crater in the northern Negev. These are so far the only outcrop localities in the Negev containing plant compressions and well-preserved sporomorphs. Their age assignments are controlled by the ammonite Knemiceras records below and above the plant-bearing sequence in the adjacent Makhtesh Hatira. The macrofossil assemblages are strikingly different in the sandy fluvial and shaly lacustrine facies, the former being dominated by Araucaria, Athrotaxopsis, Brachyphyllum and pinnatifid Sapindopsis, comparable at the plant assemblage and leaf morphological levels to the early to early late Albian assemblage of the North American Potomac flora. The lacustrine shale macrofossil assemblages appear archaic on account of their diverse pteridophyte component and sparse angiosperm remains. A new supposedly gnetophytic genus and species Qataniaria noae Krassilov, gen. et sp. nov. is dominant in the shale horizon. The sporomorph assemblages are strongly dominated by psilate trilete spores (87-93%). In the absence of elaterate forms, the angiosperm pollen Afropollis jardinus, Pennipollis, Tricolpites spp. and Walkeripollis sp. is consistent with the early Albian age. The abundance and diversity of conifers and the prominence of the fern bog assemblage suggest a relatively humid phase of the regional Albian climates.  相似文献   

Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression   总被引：6，自引：3，他引：3  

Florian Amann  Edward Alan Button  Keith Frederick Evans  Valentin Samuel Gischig  Manfred Blümel 《Rock Mechanics and Rock Engineering》2011,44(4):415-430

The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal, underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France) in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress–strain behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress.  相似文献   

A laboratory-numerical approach for modelling scale effects in dry granular slides     

Matthew Kesseler  Valentin Heller  Barbara Turnbull 《Landslides》2018,15(11):2145-2159

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as flow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25 and 1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 10²???10³. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter et al. (Acta Mech 109:127–165, 1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as flow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects.  相似文献