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61.
Pedro Del Río Antonio Casas Juan J. Villalaín Tania Mochales Ruth Soto Belén Oliva-Urcia 《Studia Geophysica et Geodaetica》2013,57(3):442-459
Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults. 相似文献
62.
Jordi Pujadas Josep Maria Casas Josep Anton Muñoz Francese Sabat 《Geodinamica Acta》2013,26(3):195-206
AbstractThe structure of the southern Pyrenees, east of the Albanyà fault (Empordà area), consists of several Alpine thrust sheets. From bottom upwards three main structural units can be distinguished : the Roc de Frausa, the Biure-Bac Grillera and the Figueres units. The former involves basement and Paleogene cover rocks. This unit is deformed by E-W trending kilometric-scale folds, its north dipping floor thrust represents the sole thrust in this area. The middle unit is formed by an incomplete Mesozoic succession overlain by Garumnian and Eocene sediments. Mesozoic rocks internal structure consists of an imbricate stack. The floor thrust dips to the south and climbs up section southwards. The upper unit exibits the most complete Mesozoic sequence. Its floor thrust is subhorizontal. The lower and middle units thrust in a piggy-back sequence. The upper unit was emplaced out of sequence.Lower Eocene sedimentation in the Biure-Bac Grillera unit was controlled by emergent imbricate thrusts and synchronic extensional faults. One of these faults (La Salut fault) represents the boundary between a platform domain in the footwall and a subsident trough in the hangingwall. Southward thrust propagation produces the inversion of these faults and the development of cleavage-related folds in their hangingwalls (buttressing effect). This inversion is also recorded by syntectonic deposits, which have been grouped in four depositional sequences. The lower sequences represent the filling on the hangingwall trough and the upper sequences the spreading of clastics to the south once the extensional movement ends. 相似文献
63.
The use of environmental markers to identify groundwater salinization sources in a Neogene basin, Kert aquifer case, NE Morocco 总被引:1,自引:0,他引:1
M. Elgettafi A. Elmandour M. Himi A. Casas 《International Journal of Environmental Science and Technology》2013,10(4):719-728
Environmental isotopes data of oxygen and hydrogen of natural water and sulphur and oxygen of dissolved sulphate as well as characteristics of d-excess are used to illustrate the salinity origin in Kert aquifer NE Morocco. In this study, 14 groundwater samples and surface water of the Kert River were collected in the Kert plain during December 2008, and were combined with previously collected hydrochemical data. The isotope compositions of these waters range from ?5.74 to ?4.51 ‰ for oxygen and from ?40.8 to ?34.1 ‰ for hydrogen. In Kert River these values are ?6.47 ‰ for oxygen and ?47.56 ‰ for hydrogen. All the samples with a slope <8 do not fall on the meteoric water line indicating a light evaporation. Water has low and different d-excess values (ranging from +1.37 to +9.82 ‰), reflecting different climatic conditions. Based on the nitrate concentration water in the Kert aquifer comes from the modern precipitation. The isotope compositions range from ?2.2 to +16 ‰ for sulphur and from +5.02 to +13.86 ‰ for oxygen. In Kert River these values are ?4.6 and +5.3 ‰ for sulphur and oxygen, respectively. There are fairly constant difference between oxygen of water and the oxygen of sulphate suggesting a dominant control of this latter in sulphate sources. At least three major sulphate sources were identified by the isotope data from sulphate in these waters: (1) dissolved marine sulphate from the underlying upper Miocene unit; (2) dissolved sulphate from Kert River; (3) sulphate derived from oxidation of sulphur compounds in the metamorphic massif of Temsamane. The latter has a dilution role. The isotopic variations of these waters and sulphate concentration therein reflect mixing of these sources in the aquifer. 相似文献
64.
AbstractDetailed mapping of the prc-Variscan rocks exposed in the Southern Central Pyrenees reveals the occurrence of extensional tectonic contacts overprinted by main phase and pre-main phase folds. The interpretation of the former contacts as normal faults and the reinterpretation of other contacts described in the literature lead us to suggest an extensional event during Devonian and/or early Carboniferous times, prior to the contrac-tional Variscan paroxysm. 相似文献
65.
Hydropeaking power production has the potential to pose serious challenges towards hydrology, water quality and ecology in the downstream water bodies. The effects of such abrupt changes of flow in hyporheic exchange have been explored in a few cases in the literature. This paper extends previous works with a study of finer time resolution in a river of a smaller size and with different climatic characteristics, adding to the current knowledge of peaking‐hyporheic interactions. A high‐frequency logging field experiment measuring hyporheic flow and temperature was conducted on a ~30 × 20 m gravel bar frequently exposed to dry conditions because of fast and abrupt flow changes. This study demonstrates that hyporheic processes are sensitive to hydropeaking with respect to rates of change, durations and temperature. Differences BETWEEN individual events, seasons, watering and dewatering processes and positions in the river bed that can be potentially relevant to ecology were investigated. Understanding the complexity of those processes at the fine scale from the physical point of view is both important for the judgement of potential ecological impacts and for the future management of such regulated systems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
66.
J. C. Martínez Oliveros C. Lindsey H. S. Hudson J. C. Buitrago Casas 《Solar physics》2014,289(3):809-819
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) provides a new tool for the systematic observation of white-light flares, including Doppler and magnetic information as well as continuum. In our initial analysis of the highly impulsive $\mathrm{\gamma}$ -ray flare SOL2010-06-12T00:57 (Martínez Oliveros et al., Solar Phys. 269, 269, 2011), we reported the signature of a strong blueshift in the two footpoint sources. Concerned that this might be an artifact due to aliasing peculiar to the HMI instrument, we undertook a comparative analysis of Global Oscillation Network Group (GONG++) observations of the same flare, using the PArametric Smearing Correction ALgorithm (PASCAL) algorithm to correct for artifacts caused by variations in atmospheric smearing. This analysis confirms the artifactual nature of the apparent blueshift in the HMI observations, finding weak redshifts at the footpoints instead. We describe the use of PASCAL with GONG++ observations as a complement to the SDO observations and discuss constraints imposed by the use of HMI far from its design conditions. With proper precautions, these data provide rich information on flares and transients. 相似文献
67.
Alberto Sáez Blas L. Valero-Garcés Santiago Giralt Ana Moreno Roberto Bao Juan J. Pueyo Armand Hernández David Casas 《Quaternary Science Reviews》2009,28(25-26):2743-2759
Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial–interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery, inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low-latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca 9.5 cal kyr BP) and swamp and shallow lake conditions dominated till mid Holocene, partially favored by the infilling of the lacustrine basin. During the mid- to late-Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The presence of this dry mid Holocene phase, also identified in low Andean latitudes and in Patagonian mid latitudes, suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by “El Niño-like” dominant conditions have occurred at a regional scale. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2–0.8 cal kyr BP sedimentary gap. Our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the Polynesian people to the island. If it occurred at ca AD 800 it coincided with the warmer conditions of the Medieval Climate Anomaly, whereas if it took place at ca AD 1300 it was favored by enhanced westerlies at the onset of the Little Ice Age. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake. 相似文献
68.
Social Exclusion and the Disabled: An Accessibility Approach* 总被引:1,自引:0,他引:1
Irene Casas 《The Professional geographer》2007,59(4):463-477
Understanding social dimensions (e.g., transport equity) is an important aspect of sustainable development. This holistic perspective allows the use of accessibility as a tool to identify disadvantaged groups. In this article, cumulative accessibility measures are calculated for a sample of individuals who participated in a one‐day travel diary survey for the Buffalo‐Niagara region in the state of New York. These measures, which include the number of opportunities available in an individual's activity space, are used to compare the levels of access between disabled and nondisabled groups and to determine if individuals' disabilities and other characteristics are contributing factors to their exclusion. Findings show that being young, coming from a small household, possessing a driver's license, having a steady job, living in an urban setting, and being willing to travel a long distance increase the number of opportunities available. 相似文献
69.
Evaluating the importance of accessibility to congestion response using a GIS-based travel simulator
Irene Casas 《Journal of Geographical Systems》2003,5(1):109-127
This paper examines the effect of accessibility on individual response to unexpected traffic delays and congestion. The dataset
used was collected by means of a travel simulator developed within a geographic information system (GIS) environment. The
simulator models a commute trip where congestion takes place, and subjects are asked to respond by making a choice among alternative
courses of action. Available alternatives for dealing with the unexpected traffic delay include changing the location of the
planned activities or changing the activities to be performed. Accessibility to the new locations and to the different activities
is computed using a cumulative measure. Analysis using CHAID tree technique found that accessibility is a good predictor of
subjects' choice when responding to unexpected traffic delays.
Received: September 2002 / Accepted: January 2003
Support for this research by a grant from the Center of Intelligent Transportation Research of the Ohio State University
is gratefully acknowledged. The author would also like to thank Joe Weber, Mei-Po Kwan and two anonymous reviewers for their
valuable comments. 相似文献
70.
This paper aims to discuss the structural evolution of the Iberian Pyrite Belt during the Variscan Orogeny. It provides new structural data, maps and cross sections from the eastern part of the Iberian Pyrite Belt. Regional geology of the South Portuguese Zone and lithostratigraphy of the Iberian Pyrite Belt are first briefly summarised. Three roughly homoaxial deformation phases are distinguished, and are mainly characterised by south-verging multi-order folds, axial planar cleavages and thrusts. Three structural units are distinguished: the La Puebla de Guzmán and Valverde del Camino antiforms are rooted units related to the propagation of southward-directed thrust systems that may branch onto the lower décollement level of the South Portuguese Zone; El Cerro de Andévalo is a structurally higher unit, mainly composed of allochthonous D1 thrust nappes. No evidence of sinistral transpression has been found in the transected cleavage and the strike of S3 with respect to S2. Better evidence of transpression is the moderately to steeply westerly plunging folds that show S-type asymmetry in down-plunge view. Variscan deformation in the Iberian Pyrite Belt is defined as the combination of a dominant southwards shear and a sinistral E-shear caused by oblique continental collision between the South Portuguese plate and the Iberian Massif. 相似文献