Schwertmannite and hydrobasaluminite: A re-evaluation of their solubility and control on the iron and aluminium concentration in acidic pit lakes     

Javier Sánchez-España  Iñaki Yusta  Marta Diez-Ercilla 《Applied Geochemistry》2011,26(9-10):1752-1774

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Interplay of phosphogenesis and hydrothermalism in the latest Ediacaran rift of the High Atlas,Morocco     

J. Javier Álvaro  Ignacio Subías 《Journal of African Earth Sciences》2011,59(1):51-60

Two dissolution surfaces, capped by phosphatic crusts that contain up to 40 wt.% of P₂O₅, are well exposed in the latest Ediacaran Tabia Member (Adoudou Formation) of the Ouneïn region, High Atlas. Both the Tabia dolostones and capping phosphorites are crosscut by several generations of synsedimentary faults, fissures, and hydrothermal dikes hosting Cu ore bodies, in a scenario of down-faulted blocks. Stratigraphic and facies relationships suggest the preservation of a major pulse of intra-cratonic rifting, responsible for the development of an unstable carbonate platform subjected to sharp uplift and tilting perturbations and dissolution processes, associated with hydrothermal dike-swarm injection. The whole framework is sealed with the Tamjout Bed (Tifnout Member), which marks the end of abundant regional tilting (syn-rift phase) and the beginning of a thermal subsidence-dominated regime (post-rift phase) in the Moroccan margin of West Gondwana.  相似文献   

Seasonal changes and morphodynamic behavior of a high-energy mesotidal beach: case study of Charf el Akab beach on the North Atlantic coast of Morocco   总被引：1，自引：1，他引：0  

Mohammed Taaouati  Driss Nachite  Javier Benavente  Abdelmounim Elmrini 《Environmental Earth Sciences》2011,64(5):1225-1236

The morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions. Two years of seasonal surveys were carried out on Charf el Akab, a gently sloped beach in the North Atlantic coast of Morocco. The method of survey consisted of a 3D study of the beach morphological changes and provided 2 cm vertical accuracy. During the surveyed period, Charf el Akab beach underwent very energetic wave conditions, and the breaking wave height was of H _b ≥ 1.5 m. The beach is characterized by a nonpermanent swash bar and composed of well-sorted medium sand. The application of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over the studied period. Morphological changes consist of beach erosion and bar decay under high-energy waves, whereas the intertidal bar re-established and the beach recorded an accentuated accretion due to relatively fair weather conditions. The beach volume reveals a seasonal behavior; the sand accumulated during summer is dramatically removed during winter season. The range in beach sand volume from the most accreted to the most eroded conditions observed is about −5,493 m³. The average sand volume flux between surveys reaches −1 and 0.4 m²/day during peak erosion and accretion periods. The relationships between the wave forcing and the sand volume adjustments were examined. The sand volume change was found to be highly correlated (0.91) with the wave energy flux. The highest correspondence (0.95) was found between the sand flux rate and the wave energy flux. The wave forcing is expected to be the main factor governing beach morphodynamics at Charf el Akab site.  相似文献   

Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco,NE Venezuela     

Maarten Van Daele  Aurélien van Welden  Jasper Moernaut  Christian Beck  Franck Audemard  Javier Sanchez  François Jouanne  Eduardo Carrillo  Gustavo Malavé  Andrés Lemus  Marc De Batist 《Marine Geology》2011,279(1-4):37-51

The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic–stratigraphic units were identified in the upper ~ 200 m of the sedimentary infill. Detailed seismic–stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.  相似文献   

Contourites within a deep-water sequence stratigraphic framework   总被引：2，自引：2，他引：0  

Rachel Brackenridge  Dorrik A. V. Stow  F. Javier Hern��ndez-Molina 《Geo-Marine Letters》2011,31(5-6):343-360

Sequence stratigraphy has proven to be an extremely useful predictive tool in the search for hydrocarbons along the continental margins. However, of the several models in use, none includes the effects of alongslope processes in deep-water. This paper, therefore, is a first attempt to place contourite depositional systems (CDSs) firmly within a sequence stratigraphic framework, based on detailed examination of over 20 CDSs worldwide. It also presents a new view of how sea level variation influences bottom current generation and intensity. Two key controls on contourite drift formation are identified: sediment influx and bottom current velocity. Sea level directly influences the sediment influx to a basin and, therefore, the contourite response fits nicely into the downslope sequence stratigraphy model. Bottom current velocity variations in response to sea level are more complex, and two key controls are identified: (1) oceanic gateways can effectively constrict and accelerate water masses and are therefore closely associated with CDS evolution; fluctuating sea level will affect the water exchange through a gateway; (2) changing rates of bottom-water generation: some water masses appear more vigorous during periods of lowstand, whereas others appear more sluggish. In order to accommodate this variation, two new sequence stratigraphy models are herein presented, comprising both downslope and alongslope processes. The first model reveals a CDS where bottom current activity is markedly more vigorous during times of sea level highstand, whereas the second model indicates margin evolution where bottom-water currents are most vigorous during times of sea level lowstand. It is recognised that there are additional controlling factors linked to sea level variation which can significantly modify the distribution and development of contourite elements.  相似文献   

On the natural line width of absorption lines in strong magnetic stellar fields     

Javier Bonatti 《Astrophysics and Space Science》1994,214(1-2):103-114

In the last years, the interest in explaining the existence of a singularity at low frequencies ( = 0) in the differential cross section of photon scattering by electrons, in a homogeneous magnetic field, for the transitions between the Landau levelsN = 1 andN = 0, has greatly increased. It is the purpose of this paper to present a calculation of the cross section for the absorption of radiation by an electron in a strong magnetic stellar field, using the Wigner-Weisskopf approximation to better understand this kind of singularity in the Compton cross section.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992.  相似文献   

Statistical Model For the Stick-Slip Behaviour of Faults     

Javier B. Gómez  A. F. Pacheco  Antonio J. Seguí Santonja 《Geophysical Journal International》1993,113(1):115-123

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Application of cokriging techniques for the estimation of hail size     

Carme?Farnell  Tomeu?RigoEmail authorView author&#;s OrcID profile  Javier?Martin-Vide 《Theoretical and Applied Climatology》2018,131(1-2):133-151

There are primarily two ways of estimating hail size: the first is the direct interpolation of point observations, and the second is the transformation of remote sensing fields into measurements of hail properties. Both techniques have advantages and limitations as regards generating the resultant map of hail damage. This paper presents a new methodology that combines the above mentioned techniques in an attempt to minimise the limitations and take advantage of the benefits of interpolation and the use of remote sensing data. The methodology was tested for several episodes with good results being obtained for the estimation of hail size at practically all the points analysed. The study area presents a large database of hail episodes, and for this reason, it constitutes an optimal test bench.  相似文献   

Experimental study of the effect of pH on the kinetics of montmorillonite dissolution at 25 °C     

M. Luisa Rozalén  F. Javier Huertas  Patrick V. Brady  Susana García-Palma 《Geochimica et cosmochimica acta》2008,72(17):4224-4253

The effect of pH on the kinetics of smectite (K-montmorillonite) dissolution was investigated at 25 °C in batch and stirred flow-through reactors over the pH range of 1-13.5, in KNO₃ solutions. Dissolution rates were obtained based on the release of Si and Al at steady-state under far from equilibrium conditions. Dissolution was non-stoichiometric between pH 5 and 10, due to adsorption/precipitation of Al. Dissolution rates computed from batch and flow-through experiments were consistent, irrespective of the Si and Al concentrations. Sample pre-treatment and the interlayer cation do not affect the steady-state dissolution rate or stoichiometry of cation release. The rate dependence on pH can be described by: