Oxygen isotope compositions of phosphate from arvicoline teeth and Quaternary climatic changes, Gigny, French Jura     

Nicolas Navarro  Christophe Lécuyer  Sophie Montuire  Cyril Langlois 《Quaternary Research》2004,62(2):172-182

Oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high- and mid-latitudes. An oxygen isotope fractionation equation was determined by using present-day European arvicoline (rodents) tooth phosphate: δ¹⁸O_p = 20.98(±0.59) + 0.572(±0.065) δ¹⁸O_w. This fractionation equation was applied to the Late Pleistocene karstic sequence of Gigny, French Jura. Comparison between the oxygen isotope compositions of arvicoline tooth phosphate and Greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence. According to the δ¹⁸O value of meteoric water-mean air temperature relationships, the δ¹⁸O value of arvicoline teeth records variations in mean air temperatures that range from 0° to 15°C.  相似文献   

DFT study of the cation arrangements in the octahedral and tetrahedral sheets of dioctahedral 2:1 phyllosilicates     

Alfonso Hernández-Laguna  Elizabeth Escamilla-Roa  Vicente Timón  Martin T. Dove  C. Ignacio Sainz-Díaz 《Physics and Chemistry of Minerals》2006,33(10):655-666

Quantum mechanical calculations based on the density functional theory (DFT) are used to study the crystal structures of dioctahedral 2:1 phyllosilicates. The isomorphous cation substitution is investigated by exploring different substitutions of octahedral Al³⁺ by Mg²⁺ or Fe³⁺, tetrahedral substitution of Si⁴⁺ by Al³⁺, and different interlayer cations (IC) (Na⁺, K⁺, Ca²⁺, and Mg²⁺). Samples with different kinds of layer charges are studied: only tetrahedrally charged, only octahedrally charged, or mixed octahedral/tetrahedral charged. The effect of the relative arrangements of these substitutions on the lattice parameters and total energy is studied. The experimental observation of segregation tendency of Fe³⁺ and dispersion tendency of Mg²⁺ in the octahedral sheet is reproduced and explained with reference to the relative energies of the octahedral cation arrangements. These energies are higher than those due to the IC/tetrahedral and IC/octahedral relative arrangements. The tetrahedral and octahedral substitutions that generate charged layers also tend to be dispersed. The octahedral cation exchange potentials change with the IC-charge/ionic radius value.  相似文献   

Microdeformation of lacustrine laminite sequences from Late Miocene formations of SE Spain: an interpretation of loop bedding   总被引：2，自引：0，他引：2  

Jose P. Calvo  Miguel Rodriguez-Pascua  Silvia Martin-Velazquez  Sergio Jimenez  & Gerardo De Vicente 《Sedimentology》1998,45(2):279-292

Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Híjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently stratified lake developed in a rapidly subsiding basin limited by 010° and 105° normal faults. As deduced from both macro- and microdeformational analyses, the basin evolved under an extensional stress field throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best definite pattern, quite similar to ' pinch and swell structures ', a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational fields. The distribution of the various loop types across the laminite sequence reflects an interplay between progressive lithification of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress field, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites.  相似文献   

Cenozoic thick-skinned deformation and topography evolution of the Spanish Central System   总被引：4，自引：2，他引：2  

G. de Vicente  R. Vegas  A. Muoz Martín  P.G. Silva  P. Andriessen  S. Cloetingh  J.M. Gonzlez Casado  J.D. Van Wees  J. lvarez  A. Carb  A. Olaiz 《Global and Planetary Change》2007,58(1-4):335

The Spanish Central System is a Cenozoic pop-up with an E–W to NE–SW orientation that affects all the crust (thick-skinned tectonics). It shows antiform geometry in the upper crust with thickening in the lower crust. Together with the Iberian Chain it constitutes the most prominent mountainous structure of the Pyrenean foreland.The evolutionary patterns concerning the paleotopography of the interior of the Peninsula can be established by an analysis of the following data: gravimetric, topographical, macro and micro tectonic, sedimentological (infilling of the sedimentary basins of the relative foreland), P–T–t path from apatite fission tracks, paleoseismic and instrumental seismicity.Deformation is clearly asymmetric in the Central System as evidenced by the existence of an unique, large (crustal-scale) thrust at its southern border, while in the northern one there is a normal sequence of north verging thrusts, towards the Duero Basin, whose activity ended during the Lower Miocene. This deformation was accomplished under triaxial compression, Oligocene–Lower Miocene in age, marked by NW–SE to NNW–SSE shortening. Locally orientations of paleostresses deviate from that of the regional tensor, following a period of relative tectonic quiescence. During the Upper Miocene–Pliocene, a reactivation of constrictive stress occurred and some structures underwent rejuvenation as a consequence of the action of tectonic stresses similar to those of today (uniaxial extension to strike–slip with NW–SE shortening direction). However, the westernmost areas show continuous activity throughout the whole of the Tertiary, with no apparent pulses. At the present time there is a moderate seismic activity in the Central System related to faults that were active during the Cenozoic, with the same kinematic characteristics.  相似文献   

Simulated Urban Climate Response to Historical Land Use Modification in the Basin of Mexico   总被引：4，自引：0，他引：4  

Arón Jazcilevich  Vicente Fuentes  Ernesto Jauregui  Esteban Luna 《Climatic change》2000,44(4):515-536

Numerical simulations of thermal field variation due to land use changes, such as the reduction of the lacustrine system and the growth of the urban area, in the Basin of Mexico are presented. It is shown that the historically recorded warming in the basin could be attributed, not only to the growth of the urban area, but more importantly to the drastic reduction in the lacustrine system that existed in the basin.  相似文献   

Sedimentary response of lake El Tobar,Spain, to climate: lake level changes after the Maunder Minimum          下载免费PDF全文

Charo López‐Blanco  Julian Andrews  Paul Dennis  María Rosa Miracle  Eduardo Vicente 《第四纪科学杂志》2016,31(8):905-918

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The Cretaceous–Palaeogene boundary at Gorgonilla Island,Colombia, South America          下载免费PDF全文

Hermann D. Bermúdez  Jenny García  Wolfgang Stinnesbeck  Gerta Keller  José Vicente Rodríguez  Michael Hanel  Jens Hopp  Winfried H. Schwarz  Mario Trieloff  Liliana Bolívar  Francisco J. Vega 《地学学报》2016,28(1):83-90

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit.  相似文献   

Exploring the relationships between perceived neighborhood boundaries and street network orientation     

Vicente Tang  Marco Painho 《Transactions in GIS》2023,27(3):877-899

The neighborhood is a core unit of analysis in urban research, planning, and policy-making. However, perceptual and historical processes oftentimes result in neighborhoods that are not tied to sub-urban jurisdictions. For instance, historic neighborhoods might lack official spatial definitions, hampering neighborhood-based tasks in local offices. In this case, urban practitioners can benefit from readily available spatial proxies, such as the local street network. In this study, we conducted an exploratory analysis that combines neighborhood mapping and street network modeling. By retrieving participants' sketched boundaries and quantifying spatial orientations of sketched polygons and local network patterns, we were able to measure and compare the relationships between the urban fabric and the perceived extents of two historic neighborhoods in Lisbon, Portugal. The results provided insights for enhancing existing definitions of non-official neighborhoods, outlining new urban districts as well as for discussions about the role of the urban form in shaping people's perceptions.  相似文献   

Evolution of vegetation activity on vegetated,eroded, and erosion risk areas in the central Spanish Pyrenees,using multitemporal Landsat imagery     

L.C. Alatorre  S. Beguería  S. Vicente‐Serrano 《地球表面变化过程与地形》2011,36(3):309-319

The temporal evolution of vegetation activity on various land cover classes in the Spanish Pyrenees was analyzed. Two time series of the normalized difference vegetation index (NDVI) were used, corresponding to March (early spring) and August (the end of summer). The series were generated from Landsat TM and Landsat ETM+ images for the period 1984–2007. An increase in the NDVI in March was found for vegetated areas, and the opposite trend was found in both March and August for degraded areas (badlands and erosion risk areas). The rise in minimum temperature and the time variation of the cloud cover during the study period appears to be the most important factors explaining increased NDVI in the vegetated areas. In degraded areas, no climatic or topographic variable was associated with the negative NDVI trend, which may be related to erosion processes taking place in these regions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

FIRST RESULTS FROM VIRGO,THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO   总被引：1，自引：0，他引：1  

Fröhlich  Claus  Andersen  Bo N.  Appourchaux  Thierry  Berthomieu  Gabrielle  Crommelynck  Dominique A.  Domingo  Vicente  Fichot  Alain  Finsterle  Wolfgang  Gómez  Maria F.  Gough  Douglas  Jiménez  Antonio  Leifsen  Torben  Lombaerts  Marc  Pap  Judit M.  Provost  Janine  Roca Cortés  Teodoro  Romero  José  Roth  Hansjörg  Sekii  Takashi  Telljohann  Udo  Toutain  Thierry  Wehrli  Christoph 《Solar physics》1997,170(1):1-25

First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation.  相似文献