Morphology and sedimentology of a complex debris flow in a clay‐shale basin     

Alexandre Remaître  Jean-Philippe Malet  Olivier Maquaire 《地球表面变化过程与地形》2005,30(3):339-348

Coupling morphological, sedimentological, and rheological studies to numerical simulations is of primary interest in defining debris‐flow hazard on alluvial fans. In particular, numerical runout models must be carefully calibrated by morphological observations. This is particularly true in clay‐shale basins where hillslopes can provide a large quantity of poorly sorted solid materials to the torrent, and thus change both the mechanics of the debris flow and its runout distance. In this context, a study has been completed on the Faucon stream (southeastern French Alps), with the objectives of (1) defining morphological and sedimentological characteristics of torrential watersheds located in clay‐shales, and (2) evaluating through a case study the scouring potential of debris flows affecting a clay‐shale basin. Morphological surveys, grain‐size distributions and petrographic analyses of the debris‐flow deposits demonstrate the granular character of the flow during the first hectometre, and its muddy character from there to its terminus on the debris fan. These observations and laboratory tests suggest that the contributing areas along the channel have supplied the bulk of the flow material. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Fission-track constraints on the thermal and tectonic evolution of the Apuseni Mountains (Romania)     

Alexandre Kounov  Stefan M. Schmid 《International Journal of Earth Sciences》2013,102(1):207-233

New zircon and apatite fission-track (FT) data, including apatite thermal modelling, are combined with an extensive literature survey and reconnaissance-type structural fieldwork in the Eastern Apuseni Mountains. This leads to a better understanding of the complex structural and thermal history of a key area at the boundary between two megatectonic units in the Balkan peninsula, namely the Tisza and Dacia Mega-Units. Following Late Jurassic obduction of the Transylvanian ophiolites onto a part of the Dacia Mega-Unit, that is, the Biharia nappe system, both units were buried to a minimum of 8 km during late Early Cretaceous times when these units were underthrust below the Tisza Mega-Unit consisting of the present-day Codru and Bihor nappe systems. Tisza formed the upper plate during Early Cretaceous (‘Austrian’) east-facing orogeny. Turonian to Campanian zircon FT cooling ages (95–71 Ma) from the Bihor and Codru nappe systems and the Biharia and Baia de Arie? nappes (at present the structurally lowest part of the Dacia Mega-Unit) record exhumation that immediately followed a second Cretaceous-age (i.e. Turonian) orogenic event. Thrusting during this overprinting event was NW-facing and led to the overall geometry of the present-day nappe stack in the Apuseni Mountains. Zircon FT ages, combined with thermal modelling of the apatite FT data, show relatively rapid post-tectonic cooling induced by a third shortening pulse during the latest Cretaceous (‘Laramian’ phase), followed by slower cooling across the 120°–60 °C temperature interval during latest Cretaceous to earliest Paleogene times (75–60 Ma). Cenozoic-age slow cooling (60–40 Ma) was probably related to erosional denudation postdating ‘Laramian’ large-scale updoming.  相似文献   

Style Transfer applied to CT image downscaling: a study case from Brazilian Coquinas     

Souza  João Paulo da Ponte  Avansi  Michelle Chaves Kuroda  Belila  Aline Maria Poças  Vidal  Alexandre Campane 《Computational Geosciences》2021,25(5):1457-1471

Computational Geosciences - The identification of micropore systems in carbonate rocks is an important task of image processing because of the high impact these systems cause on fluid flow....  相似文献   

New discoveries of vertebrate remains from the Triassic of Riba de Santiuste,Guadalajara (Spain)     

Mélani Berrocal-Casero  Julia Audije-Gil  Rui Alexandre Castanhinha  Juan Alberto Pérez-Valera  Vanda Faria dos Santos  Manuel Segura 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(4):526-541

The palaeontological sites of Riba de Santiuste and Sienes (Riba de Santiuste area) are located in the province of Guadalajara, Spain. They include a stratigraphic interval in Muschelkalk facies belonging to the “Cuesta del Castillo Sandstones” Formation and “Royuela Dolostones, Marls and Mudstones” Formation. These sites include numerous fossil plants, direct vertebrate remains, and vertebrate swim traces. The vertebrate remains correspond to a multitude of anatomical elements of Sauropterygia (Nothosauroidea, Placodontia) and possible Archosauria (Rauisuchia) remains. The fossil material attributed to nothosaurs includes teeth, coracoids, a thoracic vertebra, some isolated vertebral centra, humerus, rib fragments, and some dorsal and caudal vertebrae. The remains attributed to placodonts correspond to fragments of skull, quadrate, teeth and osteoderms. Other undetermined sauropterygian remains, such as ulnas, fragments of long bones, fragments of ribs, and articular facets of ribs have been also recovered. Additionally, a fragment of mandible and an intervertebral disk of indeterminate reptiles whose size could be compatible with archosaurs are also described. These bones are exceptionally well-preserved because the fossilization processes have preserved the microstructure of the tissues. The sites also show vertebrate traces, with parallel scratch impressions interpreted as swim traces. The relative stratigraphic position and the palaeontological content of these sites suggest a Ladinian age (Middle Triassic). The interpretation of the sedimentary facies here described also suggests that the sites could correspond to detrital-carbonate mixed deposits of coastal intertidal to supratidal environments.  相似文献   

Out‐of‐plane behaviour of a full scale stone masonry façade. Part 1: specimen and ground motion selection     

Alexandre A. Costa  António Arêde  Alfredo Campos Costa  Andrea Penna  Aníbal Costa 《地震工程与结构动力学》2013,42(14):2081-2095

The out‐of‐plane response of walls in existing stone masonry buildings is one of the major causes of vulnerability commonly observed in post‐earthquake damage surveys. In this context, a shaking table (ST) test campaign was carried out on a full‐scale masonry façade mainly focusing on the characterization of its out‐of‐plane overturning behaviour. The structure tested on the ST is a partial reproduction of an existing building from Azores, damaged during the 9 July 1998 Faial earthquake. The definition of the tested specimen as well as the selection of the input ground motion is reported in this paper. A specific emphasis is given to the definition of the time‐history to be applied during the tests because it was felt as an essential and crucial part of the work to obtain the desired overturning behaviour. The accelerogram to be imposed was selected from a large set of accelerograms (74) by means of a step‐by‐step procedure on the basis of several numerical analyses resorting to the rocking response of rigid blocks. A companion paper (Part 2) focuses on the ST test results and detailed data interpretation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Nitrogen uptake in light versus darkness of the seagrass Zostera noltei: integration with carbon metabolism          下载免费PDF全文

Ana Alexandre  João Silva  Rui Santos 《Marine Ecology》2016,37(5):1050-1056

We conducted a study that shows that light and dark conditions do not affect the uptake rates of ammonium and nitrate by the seagrass Zostera noltei. This is an important advantage over some seaweed species in which these rates are severely reduced at night. In the light, the ammonium uptake rates were initially higher (15 and 20 μmol·g^?1·h^?1) and stabilized at a rate of 5 μmol·g^?1·h^?1 after 1 h, whereas in the dark the rates remained constant at a rate of 10 μmol·g^?1·h^?1 over the first 180 min of incubation. The rates of nitrate uptake in the light were high within the first 120 min of incubation (7.2–11.1 μmol·g^?1·h^?1) and decreased afterwards to lower values (0.8–3.9 μmol·g^?1·h^?1), whereas in the dark the rates fluctuated around 0.0–11.1 μmol·g^?1·h^?1 throughout the whole incubation time (7 h). The soluble sugar content of Z. noltei leaves increased significantly with both ammonium and nitrate incubations in the light, indicating the metabolic outcome of photosynthesis. In the dark, there was no significant variation in either the soluble sugar or in the starch content of leaves, rhizomes or roots in either the ammonium or nitrate incubations. However, the total starch content of plants decreased at night whereas the total soluble sugars increased, suggesting a process of starch catabolism to generate energy with the consequent production of smaller monosaccharide products. The starch content of rhizomes decreased significantly during the light incubations with nitrate but not with ammonium. These results suggest that carbohydrate mobilization is necessary for Z. noltei to account for extra energetic costs needed for the uptake and assimilation of nitrate. Furthermore, our results suggest that nitrate uptake, at least during the day, requires the mobilization of starch whereas the uptake of ammonium does not.  相似文献   

Spatial Geochemistry: A Characterisation of Heterogeneity in Reference Materials     

L. Paul Bédard  Alexandre Néron 《Geostandards and Geoanalytical Research》2014,38(2):177-188

Geochemical reference materials (RMs) for microbeam techniques are typically characterised by averages and dispersion statistics (e.g., standard deviation, variance) that are calculated for a number of measurements (beam shots). It is proposed that the mapping of RMs will add spatial information that better characterises the grouping and magnitudes of the heterogeneities and provides the information necessary to define a minimum analytical mass. A simple mathematical solution is proposed, which can be easily computed and understood. The analogous notions to sill and range from geostatistics are applied to the minimum analytical mass versus the relative standard deviation. To assess grouping and magnitudes of the heterogeneities, a ‘proximity number’ is computed for each average value ± ‘n’ standard deviations (magnitude). Different chemical anomalies have been simulated to demonstrate the behaviour of the proximity number. To further test the proposed spatial geochemistry concept, sulfide‐ and oxide‐bearing RMs have been selected because many are crippled with nugget effect. They have been mapped with a micro‐XRF apparatus, and results are presented for CHR‐Bkg, CHR‐Pt+, MASS‐1, MASS‐3, WMS‐1 and WMS‐1a. MASS‐1 and MASS‐3 are the most suitable RMs for microbeam techniques. Spatial geochemistry offers a new approach to better characterise reference materials.  相似文献   

High-resolution aquifer analog of fluvial–aeolian sediments of the Guarani aquifer system     

Dominik Höyng  Fernando Mazo D’Affonseca  Peter Bayer  Edson Gomes de Oliveira  José Alexandre J. Perinotto  Fábio Reis  Holger Weiß  Peter Grathwohl 《Environmental Earth Sciences》2014,71(7):3081-3094

The Guarani aquifer system (GAS) represents one of the biggest aquifers in the world and is the most relevant groundwater resource in South America. For the first time, by combining field and laboratory measurements, a high-resolution aquifer analog model of fluvial–aeolian sediments of the GAS in São Paulo State (Brazil) is constructed. Three parallel sections of frontal outcrops, 28 m × 5.8 m, and two parallel sections of lateral outcrops, 7 m × 5.8 m, are recorded during open-pit mining of sandy sediments and describe in detail the three-dimensional distribution of the local lithofacies and hydrofacies. Variations of hydraulic conductivity, K, and porosity, n, are resolved on the centimeter scale, and the most permeable units of the fluvial–aeolian facies association are identified. The constructed aquifer analog model shows moderate hydraulic heterogeneity and a mean K value of 1.36 × 10^?4 m/s, which is greater than the reported range of K values for the entire GAS in São Paulo State. The results suggest that the examined sedimentary unit constitutes a relevant portion of the GAS in São Paulo State in the context of groundwater extraction and pollution. Moreover, the constructed aquifer analog is considered an ideal basis for future numerical model experiments, aiming at in-depth understanding of the groundwater flow and contaminant transport patterns at this GAS portion or at comparable fluvial–aeolian facies associations.  相似文献   

Constraints on the formation environment of two chondrule‐like igneous particles from comet 81P/Wild 2          下载免费PDF全文

Zack Gainsforth  Anna L. Butterworth  Julien Stodolna  Andrew J. Westphal  Gary R. Huss  Kazu Nagashima  Ryan Ogliore  Donald E. Brownlee  David Joswiak  Tolek Tyliszczak  Alexandre S. Simionovici 《Meteoritics & planetary science》2015,50(5):976-1004

Using chemical and petrologic evidence and modeling, we deduce that two chondrule‐like particles named Iris and Callie, from Stardust cometary track C2052,12,74, formed in an environment very similar to that seen for type II chondrules in meteorites. Iris was heated near liquidus, equilibrated, and cooled at ≤100 °C h^‐1 and within ≈2 log units of the IW buffer with a high partial pressure of Na such as would be present with dust enrichments of ≈10³. There was no detectable metamorphic, nebular, or aqueous alteration. In previous work, Ogliore et al. (2012) reported that Iris formed late, >3 Myr after CAIs, assuming ²⁶Al was homogenously distributed, and was rich in heavy oxygen. Iris may be similar to assemblages found only in interplanetary dust particles and Stardust cometary samples called Kool particles. Callie is chemically and isotopically very similar, but not identical to Iris.  相似文献   

On the Origin of the Spin of Planets and Stars and its Connection with Gravitomagnetism     

Alexandre Chaloum Elbeze 《Earth, Moon, and Planets》2012,108(3-4):151-163

The origin of the spin of planets and stars is, to a certain extent, still unexplained. In general, we attribute their rotation to the swirl of their constituent primitive gases. In this paper, we try to show that the rotation of celestial bodies depends only on their mass, apparent radius and tilt of their spin axes. We reach this conclusion within the framework of gravitomagnetism, implied by the Einstein’s general relativity theory (GR). Our results show that it might possible, in principle, to calculate the mass of spinning objects by measuring their apparent radius, the speed of rotation and the tilt of the axis of rotation.  相似文献