Origins and genesis of loess deposits in central Spain,as indicated by heavy mineral compositions and grain‐size variability     

Daniel Wolf  Karoline Ryborz  Thomas Kolb  Ruben Calvo Zapata  Jesús Sanchez Vizcaino  Ludwig Zller  Dominik Faust 《Sedimentology》2019,66(3):1139-1161

The formation of loess deposits strongly depends on the availability of deflatable dust‐sized material. Identification of source areas and mechanisms of dust production is essential for an appropriate characterization of related palaeoenvironmental conditions. So far, little research has been done on loess deposits in the Mediterranean region and information about mechanisms of dust production is very rare. In this context, it is not clear from where the loess deposits from the upper Tagus Basin in central Spain originated. The main objective of this study was to find out whether these loess deposits were formed primarily by mountain processes and fluvial comminution, or whether they have their origin in the weathering of Tertiary marls in the centre of the Madrid Basin. A further concern was to link the determined source areas with loess formation mechanisms and concomitant environmental contexts. Following a comprehensive approach using heavy minerals and grain‐size data, together with information on stratigraphic features and geomorphic positions, different local loess sources could be identified. This study shows that during the last 35 kyr a major proportion of the Tagus loess deposits was deflated from river floodplains, while the mountain region of the Iberian Range was identified as a significant source of respective floodplain sediments. Based on heavy mineral compositions and dating results, it was found that during Heinrich Stadial 3, sediment supply from the Iberian Range strongly increased, suggesting an environmental shift from initially warmer towards colder temperatures in late Marine Isotope Stage 3. Furthermore, it was found that grain‐size patterns clearly indicate maximum wind strengths during Heinrich Stadial 3, followed by Heinrich Stadial 2 and Heinrich Stadial 1. These results demonstrate that the formation of dust‐sized particles in this part of the Mediterranean operated similar to many other places in temperate and continental regions, and that weathering processes linked to hot and dry environments were only of minor importance.  相似文献   

Paleomagnetism of early cretaceous arapey formation (Northern Uruguay)     

Miguel Cervantes Solano  Avto Goguitchaichvili  Leda Sánchez Bettucci  Ruben Cejudo Ruiz  Manuel Calvo-Rathert  Vicente Carlos Ruiz-Martinez  Ruth Soto  Luis M. Alva-Valdivia 《Studia Geophysica et Geodaetica》2010,54(4):533-546

We report detailed rock-magnetic and paleomagnetic directional data from 35 lava flows (302 standard paleomagnetic cores) sampled in the Central-Northern region of Uruguay in order to contribute to the study of the paleosecular variation of the Earth’s magnetic field during early Cretaceous and to obtain precise Cretaceous paleomagnetic pole positions for stable South America. The average unit direction is rather precisely determined from 29 out of 35 sites. All A₉₅ confidence angles are less than 8°, which points to small within-site dispersion and high directional stability. Normal polarity magnetizations are revealed for 19 sites and 10 are reversely magnetized. Two other sites yield well defined intermediate polarities. The mean direction, supported by a positive reversal test is in reasonably good agreement with the expected paleodirection for Early Cretaceous stable South America and in disagreement with a 10° clockwise rotation found in the previous studies. On the other hand, paleomagnetic poles are significantly different from the pole position suggested by hotspot reconstructions, which may be due to true polar wander or the hotspot motion. Our data suggest a different style of secular variation during (and just before) the Cretaceous Normal Superchron and the last 5 Ma, supporting a link between paleosecular variation and reversal frequency.  相似文献   

A front-tracking method for the simulation of three-phase flow in porous media     

K.?-A.?LieEmail author  R.?Juanes 《Computational Geosciences》2005,9(1):29-59

Under certain physically reasonable assumptions, three-phase flow of immiscible, incompressible fluids can be described by a 2×2 nongenuinely nonlinear, hyperbolic system. We combine analytical solutions to the corresponding Riemann problem with an efficient front-tracking method to study Cauchy and initial-boundary value problems. Unlike finite difference methods, the front-tracking method treats all waves as discontinuities by evolving shocks exactly and approximating rarefactions by small entropy-violating discontinuities. This way, the method can track individual waves and give very accurate (or even exact) resolution of discontinuities. We demonstrate the applicability of the method through several numerical examples, including a streamline simulation of a water-alternating-gas (WAG) injection process in a three-dimensional, heterogeneous, shallow-marine formation.  相似文献   

The Influence of Hydromorphological Stressors on Estuarine Vegetation Indicators     

María Recio  Bárbara Ondiviela  Araceli Puente  Cristina Galván  Aina G. Gómez  Jose A. Juanes 《Estuaries and Coasts》2013,36(5):997-1005

Estuaries are one of the most threatened ecosystems, with a great number of stressors related to pollution, hydromorphological changes, and invasive species. However, the response of the biological indicators proposed for their ecological status assessment is not always well established. When using estuarine vegetation (saltmarshes and seagrasses) as an indicator, there are several theoretical concepts regarding the relationships between the variations of this indicator and hydromorphological stressors. It is precisely these relationships which are presented in this work. To carry out this objective, based on the first intercalibration process, a set of metrics for saltmarsh and seagrass taxonomic compositions (e.g., loss of number of taxa and richness) and abundance (e.g., relative coverage and relative extent) have been selected and applied to different estuaries located in Northern Spain. Additionally, a methodology for the hydromorphological status assessment, based on the analysis of the anthropogenic changes in the hydrodynamic and morphological estuarine characteristics (e.g., the extension of land claim areas or changes in the estuarine perimeter), has been developed and applied to these transitional water bodies in order to find a gradient of pressured sites in which we seek correlations between the vegetation metrics and hydromorphological stressors. As a result, the response of the different vegetation indicators is variable. In some cases, a negative correlation of the indicator with the pressure degree exists, whereas in other cases, the relationship is not as clear. Nonetheless, according to the results, it can be suggested that the placing of anthropogenic structures diminishes the quality of the estuarine vegetation. Therefore, to maintain a suitable environment for the estuarine vegetation seems necessary in order to reduce the number of the hydrodynamic structures which are no longer in use.  相似文献   

Magnetic and pedological characterisation of a paleosol under aridic conditions in Spain     

Francisco Bautista  Maria Felicidad Bógalo  Antonio Sánchez Navarro  Avto Goguitchaichvili  María José Delgado Iniesta  Ruben Cejudo  Purificación Marín Sanleandro  Juana María Gil  Elvira Díaz-Pereira 《Studia Geophysica et Geodaetica》2018,62(1):139-166

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Geostatistical seismic inversion for non‐stationary patterns using direct sequential simulation and co‐simulation          下载免费PDF全文

Hamid Sabeti  Ali Moradzadeh  Faramarz Doulati Ardejani  Leonardo Azevedo  Amilcar Soares  Pedro Pereira  Ruben Nunes 《Geophysical Prospecting》2017,65(Z1):25-48

Geostatistical seismic inversion methods are routinely used in reservoir characterisation studies because of their potential to infer the spatial distribution of the petro‐elastic properties of interest (e.g., density, elastic, and acoustic impedance) along with the associated spatial uncertainty. Within the geostatistical seismic inversion framework, the retrieved inverse elastic models are conditioned by a global probability distribution function and a global spatial continuity model as estimated from the available well‐log data for the entire inversion grid. However, the spatial distribution of the real subsurface elastic properties is complex, heterogeneous, and, in many cases, non‐stationary since they directly depend on the subsurface geology, i.e., the spatial distribution of the facies of interest. In these complex geological settings, the application of a single distribution function and a spatial continuity model is not enough to properly model the natural variability of the elastic properties of interest. In this study, we propose a three‐dimensional geostatistical inversion technique that is able to incorporate the reservoir's heterogeneities. This method uses a traditional geostatistical seismic inversion conditioned by local multi‐distribution functions and spatial continuity models under non‐stationary conditions. The procedure of the proposed methodology is based on a zonation criterion along the vertical direction of the reservoir grid. Each zone can be defined by conventional seismic interpretation, with the identification of the main seismic units and significant variations of seismic amplitudes. The proposed method was applied to a highly non‐stationary synthetic seismic dataset with different levels of noise. The results of this work clearly show the advantages of the proposed method against conventional geostatistical seismic inversion procedures. It is important to highlight the impact of this technique in terms of higher convergence between real and inverted reflection seismic data and the more realistic approximation towards the real subsurface geology comparing with traditional techniques.  相似文献   

Pastas: Open Source Software for the Analysis of Groundwater Time Series     

Raoul A. Collenteur  Mark Bakker  Ruben Caljé  Stijn A. Klop  Frans Schaars 《Ground water》2019,57(6):877-885

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Collapse and explosion in a rotating star     

G. Ruben  I. Tuominen 《Astronomische Nachrichten》1988,309(2):103-120

The collapse, bounce, shock wave and expansion of the envelope of a rotating star have been analysed in the adiabatic approximation using the particle-in-cell method. The bounce takes place first in the equatorial plane and a shock wave arises there which shortly afterwards crosses the surface of the star. In the envelope, and to a less extent in the remainder of the star, there is a fast and lasting meridional motion the direction of which changes. As a consequence of the fast meridional motion in the envelope, mass and angular momentum are transported towards the axis of rotation. If the initial star rotates fast enough this will cause a secondary radial expansion in the polar region and a mass ejection. These motions reduce the strong anisotropy caused originally by the equatorial expansion. Strong whirls may arise along the axis of rotation. In the remainder of the star the meridional motion becomes supersonic. The temperature in the envelope depends to a high degree on the choice of the equation of state. Massloss is proportional to the energy initially added. The final loss of angular momentum and of energy is quite large, both losses being about 25%.  相似文献