The supergene origin of ruthenian hexaferrum in Ni‐laterites          下载免费PDF全文

Thomas Aiglsperger  Joaquín A. Proenza  Salvador Galí  Jordi Rius  Francisco Longo  Cristina Domènech 《地学学报》2017,29(2):106-116

For two decades, the nature of Fe‐rich, oxygen‐bearing, Ru–Os compounds found in the supergene environment has been debated. Ru–Os–Fe‐oxides and nano‐intergrowths of ruthenium with magnetite have been proposed. We applied FE‐SEM, EMPA, μ‐Raman spectroscopy and synchrotron tts‐μXRD to Ru–Os–Fe compounds recovered from Ni‐laterites from the Dominican Republic. The results demonstrate that a significant portion of Fe exists in a common structure with the Ru–Os alloy, that is, ruthenian hexaferrum. This mineral occurs both as nanoparticles and as micrometric patches within a matrix of Fe‐oxide(s). Our data suggest that supergene ruthenian hexaferrum with a (Ru_0.4(Os,Ir)_0.1Fe_0.5)_?1.0 stoichiometry represents the most advanced weathering product of primary laurite within Ni‐laterites from the Dominican Republic.  相似文献   

Bioerosion and encrustation rates in recent mollusk death assemblages on a supratidal siliciclastic setting,Playa Norte,Veracruz State,Mexico     

Catalina Gómez-Espinosa  F. Raúl Gío-Argáez  Ester A. Farinati  Salvador Aliotta  Sergio Adrian Salgado-Souto 《Arabian Journal of Geosciences》2018,11(8):188

This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.  相似文献   

Petrographic and geochemical evidence for the formation of primary, bacterially induced lacustrine dolomite: La Roda 'white earth' (Pliocene, central Spain)   总被引：1，自引：0，他引：1  

M. Angeles García Del Cura  Jose P. Calvo  Salvador Ordóñez  Blair F. Jones  & Juan C. Cañaveras 《Sedimentology》2001,48(4):897-915

Upper Pliocene dolomites (‘white earth’) from La Roda, Spain, offer a good opportunity to evaluate the process of dolomite formation in lakes. The relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations. The La Roda Mg‐carbonates (dolomite unit) occur as a 3·5‐ to 4‐m‐thick package of poorly indurated, white, massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds. The massive dolomite beds consist mainly of loosely packed 1‐ to 2‐μm‐sized aggregates of dolomite crystals exhibiting poorly developed faces, which usually results in a subrounded morphology of the crystals. Minute rhombs of dolomite are sparse within the aggregates. Both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites. In addition, aggregates of euhedral dolomite crystals are usually present in some more clayey (sepiolite) interbeds. The thin porous carbonate (mostly dolomite) beds exhibit both euhedral and subrounded, bacterially induced dolomite crystals. The carbonate is mainly Ca‐dolomite (51–54 mol% CaCO₃), showing a low degree of ordering (degree of ordering ranges from 0·27 to 0·48). Calcite is present as a subordinate mineral in some samples. Sr, Mn and Fe contents show very low correlation coefficients with Mg/Ca ratios, whereas SiO₂ and K contents are highly correlated. δ¹⁸O‐ and δ¹³C‐values in dolomites range from ?3·07‰ to 5·40‰ PDB (mean=0·06, σ=1·75) and from ?6·34‰ to ?0·39‰ PDB (mean=?3·55, σ=1·33) respectively. Samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in ¹⁸O and ¹³C between the two minerals. The correlation coefficient between δ¹⁸O and δ¹³C for dolomite is extremely low and negative (r=?0·05), whereas it is higher and positive (r=0·47) for calcite. The lacustrine dolomite deposit from La Roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow, hydrologically closed perennial lake. The lake was supplied by highly saturated HCO₃^?/CO₃^2? groundwater that leached dolomitic Mesozoic formations. Precipitation of dolomite from alkaline lake waters took place under a semi‐arid to arid climate. However, according to our isotopic data, strong evaporative conditions were not required for the formation of the La Roda dolomite. A significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence.  相似文献   

Analyzing ice dynamics using Sentinel-1 data at the Solheimajoküll Glacier,Iceland     

Diego Gómez  Pablo Salvador  Julia Sanz  Mikhail Urbazaev  José Luis Casanova 《地理信息系统科学与遥感》2020,57(6):813-829

ABSTRACT

The climate in southern Iceland has warmed over the last 70 years, resulting in accelerated glacier dynamics at the Solheimajoküll glacier. In this study, we compare glacier terminus locations from 1973 to 2018, to changes in climate across the study area, and we derive ice-surface velocities (2015–2018) from satellite remote-sensing imagery (Sentinel-1) using the offset-tracking method. There have been two regional temperature trends in the study period: cooling (1973–1979) and warming (1980–2018). Our results indicate a time lag of about 20 years between the onset of glacier retreat (?53 m/year since 2000) and the inception of the warming period. Seasonally, the velocity time series suggest acceleration during the summer melt season since 2016, whereas glacier velocities during accumulation months were constant. The highest velocities were observed at high elevations where the ice-surface slope is the steepest. We tested several scenarios to assess the hydrological time response to glacier accelerations, with the highest correlations being found between one and 30 days after the velocity estimates. Monthly correlation analyses indicated inter-annual and intra-annual variability in the glacier dynamics. Additionally, we investigate the linkage between glacier velocities and meltwater outflow parameters as they provide useful information about internal processes in the glacier. Velocity estimates positively correlate with water level and negatively correlate with water conductivity between April and August. There is also a disruption in the correlation trend between water conductivity and ice velocity in June, potentially due to a seasonal release of geothermal water.  相似文献   

Diagnosis of trace metal contamination in sediments: the example of Ensenada and El Sauzal, two harbors in Baja California, Mexico   总被引：1，自引：0，他引：1  

Huerta-Diaz MA  Delgadillo-Hinojosa F  Hernández-Ayón M  Segovia-Zavala JA  García-Esquivel Z  López-Zárate H  Siqueiros-Valencia A  Galindo-Bect S 《Marine environmental research》2008,66(3):345-358

Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)(sample) ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EF(Me)=(Me/Al)(sample)/(Me/Al)(shale)] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake.  相似文献   

Motif Discovery on Seismic Amplitude Time Series: The Case Study of Mt Etna 2011 Eruptive Activity     

Carmelo Cassisi  Marco Aliotta  Andrea Cannata  Placido Montalto  Domenico Patanè  Alfredo Pulvirenti  Letizia Spampinato 《Pure and Applied Geophysics》2013,170(4):529-545

Algorithms searching for similar patterns are widely used in seismology both when the waveforms of the events of interest are known and when there is no a priori-knowledge. Such methods usually make use of the cross-correlation coefficient as a measure of similarity; if there is no a-priori knowledge, they behave as brute-force searching algorithms. The disadvantage of these methods, preventing or limiting their application to very large datasets, is computational complexity. The Mueen–Keogh (MK) algorithm overcomes this limitation by means of two optimization techniques—the early abandoning concept and space indexing. Here, we apply the MK algorithm to amplitude time series retrieved from seismic signals recorded during episodic eruptive activity of Mt Etna in 2011. By adequately tuning the input to the MK algorithm we found eight motif groups characterized by distinct seismic amplitude trends, each related to a different phenomenon. In particular, we observed that earthquakes are accompanied by sharp increases and decreases in seismic amplitude whereas lava fountains are accompanied by slower changes. These results demonstrate that the MK algorithm, because of its particular features, may have wide applicability in seismology.  相似文献   

Efficient conceptual model for simulating the effect of aquifer heterogeneity on natural groundwater discharge to rivers   总被引：1，自引：0，他引：1  

David Pulido-Velazquez  Carlos Llopis-Albert  Salvador Peña-Haro  Manuel Pulido-Velazquez 《Advances in water resources》2011,34(11):1377-1389

When linearity can be assumed (linear response of heads to stresses), stream–aquifer flow exchange can be simulated as the drainage of a number of independent linear reservoirs. This conceptual model, which can be mathematically deduced in a univocal way from an eigenvalue solution of the linear groundwater flow problem, facilitates the understanding of the physical phenomenon and the analysis of influencing factors. The number of reservoirs required to simulate stream depletion in some ideal homogeneous cases of stream–aquifer connection was analyzed in detail in a previous investigation using analytical eigenvalue solutions [16]. However, most aquifers are heterogeneous in nature and numerical solutions must be employed to analyze whether they could also be simulated using few reservoirs. This paper presents a stochastic analysis of the influence of heterogeneity on the simulation of natural groundwater discharges in aquifers connected to rivers, as a series of linear reservoirs. A Monte-Carlo approach was employed to perform this study. The results show that, on a monthly time scale, many cases (even heterogeneous aquifers) can be simulated using just a few reservoirs with sufficient accuracy and at minimum computational cost. Therefore, this modeling technique can be useful to efficiently simulate the integrated management of complex water resources systems at the basin scale (with many aquifers, reservoirs, demands, etc.) that need to simultaneously consider surface and groundwater flow and stream–aquifer interaction.  相似文献   

Can we learn from the past? Four hundred years of changes in adaptation to floods and droughts. Measuring the vulnerability in two Hispanic cities   总被引：2，自引：0，他引：2  

Salvador Gil-Guirado  José-Antonio Espín-Sánchez  María Del Rosario Prieto 《Climatic change》2016,139(2):183-200

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Climate effects on soil erodibility   总被引：3，自引：0，他引：3  

M. P. Salvador Sanchis  D. Torri  L. Borselli  J. Poesen 《地球表面变化过程与地形》2008,33(7):1082-1097

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Modelling increased soil cohesion due to roots with EUROSEM   总被引：3，自引：0，他引：3  

S. De Baets  D. Torri  J. Poesen  M. P. Salvador  J. Meersmans 《地球表面变化过程与地形》2008,33(13):1948-1963

As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root‐permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root‐permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap‐rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献