La compression pré-campano-maastrichtienne dans le Mésozoïque des Andes de Bolivie : l’exemple de Tica Tica (20°01’lat. S et 66°17’ long. W)     

C. Martinez  G. Laubacher 《Geodinamica Acta》2013,26(4):261-278

Résumén

Dans la Cordillère Orientale des Andes de Bolivie, le Mésozoïque est eonservé le plus souvent dans des synclinaux discontinus, fréquemment chevauchés par des écailles de Paléozoïqne. Les sédiments mésozoïques, marins et continentaux de plateforme d’arrière-arc, ont jusqu’à présent été considérés comme déposés en régime extensif. Ils recouvrent en discordance le Paléozoïque plissé et l’aillé à l’Hercynien et, postérieurement, profondément érodé avant la sédimentation mésozoïque. Des paléofailles majeures N-S, NW-SE et NE-SW, héritées de structurations antérieures, ont influencé l’évolution géodynamique du bassin mésozoïque depuis la lin du Jurassique.

Dans la partie méridionale de la Cordillère Orientale, la région de Tica Tica présente de nombreux indices de serrage synsédimentaire depuis le début des dépôts mésozoïques jusqu’à la discordance campano-maastriehtienne (phase « péruvienne »). Le domaine de la Cordillère Orientale, avant-pays du bassin d’arrière-arc chiléno-péruvien, peut être ainsi interprété comme un secteur en compression sur lequel les transgressions successives, au Cénomanien, au Turonien et au Campano-Maastrichtien. soulignent divers instants d’un processus pratiquement continu de déformation.

Pendant le Tertiaire, les chevauchements andins réactivent les accidents majeurs préexistants : ils en inversent le mouvement, ou les déforment, ou bien les utilisent comme zones de coulissage. Ainsi, contrairement à ce qui a pu être proposé, le raccourcissement de la chaîne des Andes boliviennes, initié à la fin du Jurassique et faisant intervenir des fractures profondes, implique une participation, non seulement de la totalité de la pile séilimeutaire, mais très vraisemblablement aussi de son substratum précambrien comme c’est le cas dans le Nord-Ouest argentin.  相似文献   

Visual versus digital analysis for vegetation mapping: Some examples on central Spain     

Emilio Chuvieco  Javier Martinez Vega 《国际地球制图》2013,28(3):21-30

Digital processing of Landsat images has been considered the most appropriate interpretation method for vegetation mapping. However, digital processing presents several difficulties: (i) it demands significant inversions, with respect both the images and the equipment; (ii) it presents problems to discriminate heterogeneous categories, and (iii) it requires much more training effort.

Visual analysis, on the other hand, is less demanding both in economic investments and training. Therefore, it is a fruitful alternative to digital mapping, especially when it is applied to small and medium scale inventories. A consistent methodology for visual interpretation of vegetation categories is presented in this paper. Benefits and disadvantages of this procedure are analyzed, as well as keys‐for visual identification of land cover categories. A TM Quarter of scene on Central Spain is presented as an example of this method. Two false‐color images from different seasons were interpreted at 1: 250,000 scale. Fourteen land cover categories were identified, yielding 83.03% of final accuracy.  相似文献   

The Hydrologic Importance of Small- and Medium-Sized Dams: Examples from Texas     

Anne Chin  Laura R. Laurencio  Adriana E. Martinez 《The Professional geographer》2013,65(2):238-251

Studies of the effects of dams have emphasized large and very large dams; less well understood are the impacts caused by smaller dams. Using Texas as an example area, this article highlights the role of small- and medium-sized dams in affecting the surface hydrology of river systems. Analysis of data from the National Inventory of Dams (NID) in a geographic information system showed that small and medium dams comprise about 97 percent of the dams registered in Texas. A small-or medium-sized dam is found approximately every 100 km² of area and about 120 km of river length. Different from large dams, which affect water storage the most, the major impact of these smaller dams is fragmentation of river landscapes. Analysis of data for dams extracted from digital orthoquads and for water bodies from the National Hydrography Dataset indicates that the extent of river fragmentation is likely greater than that suggested by data from the NID, because the NID underrepresents the smaller dams. Such extent of river fragmentation can degrade stream habitats and pose barriers to the migration of aquatic species and transport of sediment. Because small and medium dams are largely built for fire protection and stock ponds, mitigating the impacts associated with these dams likely involves working with the private individuals who own them.  相似文献   

The new accelerograph network for Santa Fe De Bogota, Colombia and implications for microzonation     

Anibal Ojeda  Samuel Martinez  Maria Bermudez  Kuvvet Atakan 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):791-797

The new accelerographic network of Santa Fe de Bogotá is composed of 29 three-component stations with sensors at the surface and three additional six-component borehole stations with three sensors at the surface and three at depth (115, 126 and 184 m). In total, 32 stations have been operative in the metropolitan area of Bogotá since 1999. During this period of time, a significant number of weak motion are recorded and used for a preliminary analysis of local site effects. Using the SH-wave response spectra we verify the behavior of the different seismic zones proposed by the previous microzonation study of the city. A comparison between normalized SH-wave response spectra and the normalized design spectra for each zone clearly depicts that parts of the design spectra should be revised, as well as the boundaries between different zones may require some changes. The spectral amplification levels reach up to a factor of 5. The predominant periods obtained by the amplification spectra in different stations in the city, show variability from 0.3 to 3.0 s. A comparison is also made between the predominant periods obtained using H/V spectral ratios of microtremors and those using weak motion. In general, microtremors tend to predict slightly lower values of dominant periods than those calculated by the weak motion spectra. However, there is a general correlation between the two data sets. Using the data recorded by one of the borehole station, an equivalent linear seismic response analysis was conducted. The modeled and recorded response spectra show similarities in period peaks, however, the modeled soil amplification is underestimated for periods less than 0.8 s. Since the available record is weak motion which represents mostly the linear response of the soils, further analysis is required.  相似文献   

Dynamic sea level changes following changes in the thermohaline circulation   总被引：3，自引：2，他引：1  

Anders Levermann  Alexa Griesel  Matthias Hofmann  Marisa Montoya  Stefan Rahmstorf 《Climate Dynamics》2005,24(4):347-354

Using the coupled climate model CLIMBER-3, we investigate changes in sea surface elevation due to a weakening of the thermohaline circulation (THC). In addition to a global sea level rise due to a warming of the deep sea, this leads to a regional dynamic sea level change which follows quasi-instantaneously any change in the ocean circulation. We show that the magnitude of this dynamic effect can locally reach up to ~1 m, depending on the initial THC strength. In some regions the rate of change can be up to 20–25 mm/yr. The emerging patterns are discussed with respect to the oceanic circulation changes. Most prominent is a south-north gradient reflecting the changes in geostrophic surface currents. Our results suggest that an analysis of observed sea level change patterns could be useful for monitoring the THC strength.  相似文献   

Estimation de la température maximale d'enfouissement du Toarcien et du Callovo-Oxfordien au centre du bassin de Paris par les marqueurs organiques     

Cédric Ménétrier  Marcel Élie  Luis Martinez  Antoine Le Solleuz  Jean-Robert Disnar  Cécile Robin  François Guillocheau  Christophe Rigollet 《Comptes Rendus Geoscience》2005,337(15):1323-1330

The thermal history of the central part of the Paris basin is reconstructed using C₃₁ hopane $\mathrm{S}/\mathrm{R}$ isomerisation ratios and organic matter transformation ratios measured on Lower Toarcian and Callovo-Oxfordian samples. Maximum burial palaeotemperatures range between 90 and 115?°C for the Toarcian shales, and between 75 and 95?°C for the Callovo-Oxfordian samples, from the East to the centre of the basin, respectively. The amount of Late Cretaceous erosion was evaluated to be between ca. 400 to 600 m in the eastern part of the studied area and 100 to 300 m in the centre of the basin. To cite this article: C. Ménétrier et al., C. R. Geoscience 337 (2005).  相似文献   

Flickering in V841 Ophiuchi     

Brian Warner  Peter Martinez  Darragh O'Donoghue 《Astrophysics and Space Science》1995,226(1):27-30

Light curves of the nova remnant V841 Oph, obtained on seven nights in 1985, are presented. Flickering occurs on all timescales from at least as short as 100 s to many hours. No periodic modulations were found. Further spectroscopic or infrared observations are recommended in order to verify the orbital period.  相似文献   

Publisher's announcement     

Peter Martinez 《Astrophysics and Space Science》1989,155(1):v-v

Publisher's announcement  相似文献   

Structural evolution of the Llanos foothills, Eastern Cordillera, Colombia     

Jaime A. Martinez   《Journal of South American Earth Sciences》2006,21(4):510-520

The Llanos foothills are located in the frontal thrust zone of the Eastern Cordillera in Colombia in a complex environment that BP has been exploring actively since 1988. This exploration has resulted in the discovery of several fields with a variety of hydrocarbon fluids (gas condensate and volatile oil) in very tight quartz-arenites. The structural style and complexity of this fold-and-thrust belt changes along the trend from single frontal structures to an imbricate of up to five thrust sheets in a triangle zone. In highly complex environments, the seismic image quality is poor, and interpretation becomes very challenging. The structural models of the area have evolved as more data have been acquired. The initial structural model required inversion of the basin at the end of the Andean orogeny. The structural style changed to an in-sequence imbricate thrust stack with very long, trailing back limbs that return to regional elevation and finalize in a tighter structures with short back limbs. The concept of early deformation and multiple phases has been introduced. Three main phases have been distinguished: (1) an early event during the deposition of the Lower Carbonera (39–29 Ma), with incipient structures formed to create syntectonic deposition; (2) a phase of steady subsidence that increased notably at the end of the period (29–7 Ma); and (3) the latest phase (7–0 Ma), when most deformation and uplifting occurred. The migration of hydrocarbons happened simultaneously with the deformation, and its final distribution, amount, and variation in composition is related to the structural evolution of the area.  相似文献   

Projection of future climate change conditions using IPCC simulations, neural networks and Bayesian statistics. Part 2: Precipitation mean state and seasonal cycle in South America     

Jean-Philippe Boulanger  Fernando Martinez  Enrique C. Segura 《Climate Dynamics》2007,28(2-3):255-271

Evaluating the response of climate to greenhouse gas forcing is a major objective of the climate community, and the use of large ensemble of simulations is considered as a significant step toward that goal. The present paper thus discusses a new methodology based on neural network to mix ensemble of climate model simulations. Our analysis consists of one simulation of seven Atmosphere–Ocean Global Climate Models, which participated in the IPCC Project and provided at least one simulation for the twentieth century (20c3m) and one simulation for each of three SRES scenarios: A2, A1B and B1. Our statistical method based on neural networks and Bayesian statistics computes a transfer function between models and observations. Such a transfer function was then used to project future conditions and to derive what we would call the optimal ensemble combination for twenty-first century climate change projections. Our approach is therefore based on one statement and one hypothesis. The statement is that an optimal ensemble projection should be built by giving larger weights to models, which have more skill in representing present climate conditions. The hypothesis is that our method based on neural network is actually weighting the models that way. While the statement is actually an open question, which answer may vary according to the region or climate signal under study, our results demonstrate that the neural network approach indeed allows to weighting models according to their skills. As such, our method is an improvement of existing Bayesian methods developed to mix ensembles of simulations. However, the general low skill of climate models in simulating precipitation mean climatology implies that the final projection maps (whatever the method used to compute them) may significantly change in the future as models improve. Therefore, the projection results for late twenty-first century conditions are presented as possible projections based on the “state-of-the-art” of present climate modeling. First, various criteria were computed making it possible to evaluate the models’ skills in simulating late twentieth century precipitation over continental areas as well as their divergence in projecting climate change conditions. Despite the relatively poor skill of most of the climate models in simulating present-day large scale precipitation patterns, we identified two types of models: the climate models with moderate-to-normal (i.e., close to observations) precipitation amplitudes over the Amazonian basin; and the climate models with a low precipitation in that region and too high a precipitation on the equatorial Pacific coast. Under SRES A2 greenhouse gas forcing, the neural network simulates an increase in precipitation over the La Plata basin coherent with the mean model ensemble projection. Over the Amazonian basin, a decrease in precipitation is projected. However, the models strongly diverge, and the neural network was found to give more weight to models, which better simulate present-day climate conditions. In the southern tip of the continent, the models poorly simulate present-day climate. However, they display a fairly good convergence when simulating climate change response with a weak increase south of 45°S and a decrease in Chile between 30 and 45°S. Other scenarios (A1B and B1) strongly resemble the SRES A2 trends but with weaker amplitudes.  相似文献