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排序方式: 共有196条查询结果,搜索用时 31 毫秒
81.
E. Terán-Bobadilla J. H. Abundis-Patiño C. Añorve C. R. Moraila F. Ortega-Gutiérrez M. A. Aragón-Calvo 《Earth, Moon, and Planets》2017,120(2):101-111
Tridimensional model with large level of detail and reliability of the Bacubirito meteorite is determined by laser scanner measurements. By means of this model and densities published in the literature, we estimate the mass, main geometrical quantities, and regmaglypts distribution on the meteorite. A Monte Carlo method is proposed for uncertainty estimations of the derived geometrical magnitudes. The Bacubirito meteorite mass is m = 19.43 ± 0.51 tons with a maximum length of 4.130 ± 0.005 m; Bacubirito is set as the world’s fifth largest and the longest reported to date. 相似文献
82.
Irrigation effects on the salinity of the Arba and Riguel Rivers (Spain): present diagnosis and expected evolution using geochemical models 总被引:2,自引:0,他引:2
J.?CausapéEmail author L.?Auqué Ma?J.?Gimeno J.?Mandado D.?Quílez R.?Aragüés 《Environmental Geology》2004,45(5):703-715
This work diagnoses the present salinity of the Riguel and Arba Rivers (Spain) and predicts its expected evolution using geochemical models applied to the modernization of the actual Bardenas I and the completion of irrigation in the Bardenas II irrigation districts. The results show a progressive increase in salinity (from 0.39 to 2.21 dS/m electrical conductivity) in the Riguel-Arba system, due to the cumulative collection of irrigation return flows and its progression towards more saline facies. The Bardenas I modernization, involving an increase in irrigation efficiency from 50 to 90%, will decrease the volume and salinity of the Riguel River by 30%. In contrast, irrigation of the new 24,000 ha Bardenas II land will increase the flow (12%) and salinity (21%) of the Arba River. Geochemical models may help in providing sensible estimates on the impact of irrigation on the salinity of the receiving water bodies. 相似文献
83.
84.
Salvador E. Lluch-Cota Eugenio A. Aragón-Noriega David Aurioles-Gamboa Richard C. Brusca Roberto Cortés-Altamirano Alfonso Esquivel-Herrera Michel E. Hendrickx Hugo Herrera-Cervantes Miguel Lavín Daniel B. Lluch-Cota Silvio G. Marinone Sofia Ortega-García Alejandro Parés-Sierra Mauricio Ramírez-Rodríguez Richard A. Schwartzlose Arturo P. Sierra-Beltrán 《Progress in Oceanography》2007,73(1):1-26
The Gulf of California is unique because of its geographical location and conformation. It hosts diverse ecosystems and important fisheries that support industry and provide livelihood to coastal settlements. It is also the site of interests and problems, and an intense interaction among managers, producers, and conservationists. In this report, we scrutinize the abiotic (hydrography, climate, ocean circulation, and chemistry) and biotic (phyto- and zooplankton, fish, invertebrates, marine mammals, birds, and turtles) components of the marine ecosystem, and some particular aspects of climate variability, endemisms, harmful algal blooms, oxygen minimum layer, and pollution. We also review the current conditions and conflicts around the main fisheries (shrimp, small and large pelagic fishes, squid, artisanal and sportfishing), the most important human activity in the Gulf of California. We cover some aspects of management and conservation of fisheries, especially the claimed overexploitation of fish resources and the ecosystems, and review proposals for creating networks of marine protected areas. We conclude by identifying main needs for information and research, particularly the integration of data bases, the implementation of models and paleoreconstructions, establishment of monitoring programs, and the evaluation of fishing impacts and management actions. 相似文献
85.
86.
Lee J. Arnold Martina Demuro Marta Navazo Alfonso Benito‐Calvo Alfredo Pérez‐González 《Boreas: An International Journal of Quaternary Research》2013,42(2):285-305
In this study we present optically stimulated luminescence (OSL) dating results obtained at one of the most important open‐air Middle Palaeolithic sites in the Sierra de Atapuerca foothills – Hotel California. We also assess the possibility of obtaining extended‐range OSL chronologies for a nearby Middle Pleistocene fluvial deposit using several novel methods, namely OSL dating of individual quartz ‘supergrains’, multi‐grain aliquot thermally transferred OSL (TT‐OSL) dating and the first application of a single‐grain TT‐OSL dating procedure. Four single‐grain OSL ages constrain the Middle Palaeolithic occupation of Hotel California to between 71±6 and 48±3 ka. The Hotel California single‐grain equivalent dose (De) distributions are highly overdispersed and contain several dose populations, which are probably attributable to post‐depositional sediment mixing, partial bleaching and intrinsic scatter. The reliability of multi‐grain aliquot OSL dating is compromised by the complex underlying De dispersion affecting these samples, as well as by biasing multi‐grain averaging effects. Extended‐range OSL and TT‐OSL chronologies for the nearby Pico River terrace are consistent with each other and with broad independent age control. These experimental approaches yield a weighted average age of 348±16 ka for terrace TA9 of the Arlanzón River sequence. Our results highlight the benefits of comparing ages obtained using several OSL methodologies to improve the robustness of luminescence chronologies. They also demonstrate the potential that single‐grain OSL techniques offer for establishing improved age constraints on the many other Middle Palaeolithic sites found at Atapuerca and elsewhere across north‐central Spain. 相似文献
87.
Donají García-Alonso Carles Canet Eduardo González-Partida Ruth Esther Villanueva-Estrada Rosa María Prol-Ledesma Pura Alfonso Juan Antonio Caballero-Martínez Rufino Lozano-Santa Cruz 《Journal of South American Earth Sciences》2011,31(4):432-443
In the San Marcos ranges of Cuatrociénegas, NE Mexico, several sediment-hosted copper deposits occur within the boundary between the Coahuila Block, a basement high mostly granitic in composition and Late Paleozoic to Triassic in age, and the Mesozoic Sabinas rift basin. This boundary is outlined by the regional-scale synsedimentary San Marcos Fault. At the basin scale, the copper mineralization occurs at the top of a ~1000 m thick red-bed succession (San Marcos Formation, Berrisian), a few meters below a conformable, transitional contact with micritic limestones (Cupido Formation, Hauterivian to Aptian). It consists of successive decimeter-thick roughly stratiform copper-rich horizons placed just above the red-beds, in a transitional unit of carbonaceous grey-beds grading to micritic limestones. The host rocks are fine- to medium-grained arkoses, with poorly sorted and subangular to subrounded grains. The detrital grains are cemented by quartz and minor calcite; besides, late iron oxide grain-coating cement occurs at the footwall unmineralized red-beds. The source area of the sediments, indicated by their modal composition, is an uplifted basement. The contents of SiO2 (40.70–87.50 wt.%), Al2O3 (5.91–22.00 wt.%), K2O (3.68–12.50 wt.%), Na2O (0.03–2.03 wt.%) and CaO (0.09–3.78 wt.%) are within the ranges expected for arkoses. Major oxide ratios indicate that the sedimentary-tectonic setting was a passive margin.The outcropping copper mineralization essentially consists in a supergene assemblage of chrysocolla, malachite and azurite. All that remains of the primary mineralization are micron-sized chalcocite grains shielded by quartz cement. In addition, pyrite subhedral grains occur scattered throughout the copper-mineralized horizons. In these weathered orebodies copper contents range between 4.24 and 7.72 wt.%, silver between 5 and 92 ppm, and cobalt from 8 to 91 ppm. Microthermometric measurements of fluid inclusions in quartz and calcite crystals from footwall barren veinlets gave temperatures of homogenization between 98 °C and 165 °C, and ice-melting temperatures between ?42.5 °C and ?26.1 °C.The primary copper mineralization formed during the early diagenesis, contemporary with the active life of the Sabinas Basin. The mineralizing fluids were dense, near neutral, moderately oxidized brines that originally formed from seawater that, driven by gravity, infiltrated to the deepest parts of the basin and dissolved evaporites. As a result, they became hydrothermal fluids of moderate temperature capable of leaching high amounts of copper. The source of this metal could be mafic detrital grains and iron oxides of the underlying Jurassic and Lower Cretaceous red-beds. Copper precipitation took place when the brines passed through the redox boundary marked by the transition from red- to grey-beds. The upward movement of the brines was promoted by a high heat flow that allowed their convective circulation and their ascent along the synsedimentary San Marcos Fault. 相似文献
88.
Within classical iterative subdomain methods, the problems in the subdomains are solved alternately by only using data on the interface provided from the other subdomains. Methods of this type for the Stokes–Darcy problem that use Robin boundary conditions on the interface are reviewed. Their common underlying structure and their main differences are identified. In particular, it is clarified that there are different updating strategies for the interface conditions. For small values of fluid viscosity and hydraulic permeability, which are relevant in applications from geosciences, it is shown in numerical studies that only one of these updating strategies leads to an efficient numerical method, if it is used with appropriate parameters in the Robin conditions. 相似文献
89.
In the present paper the effect of an abrupt change of the atmospheric radiative forcing is investigated by means of a global climate model that includes a mixed layer ocean. In assessing if, under such a change, the model response has a bifurcation point, the steady solution is studied for a sudden decrease of CO2 concentration from its actual value. It is found that there is a critical threshold for CO2 content below which the model ends up to a snowball Earth. It occurs for a few percentage changes of CO2 concentration around the threshold because the model strongly depends on the relationship among atmospheric temperature, water vapor content and the sudden ice-albedo feedback activation, even in the subtropical regions. Moreover, results suggest that the transition to ice-covered Earth is clearly favoured when Q-flux corrections (i.e. the parameterization of ocean heat transports) are removed. 相似文献
90.
Gabriella De Lucia Bianca M. Poggianti Alfonso Aragón-Salamanca Simon D. M. White Dennis Zaritsky Douglas Clowe Claire Halliday Pascale Jablonka Anja von der Linden Bo Milvang-Jensen Roser Pelló Gregory Rudnick Roberto P. Saglia Luc Simard 《Monthly notices of the Royal Astronomical Society》2007,374(3):809-822