Geological,geochemical and mineralogical features of some bauxite deposits from Nurra (Western Sardinia,Italy): insights on conditions of formation and parental affinity

Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al₂O₃ and residual ‘immobile’ elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO₂ and Fe₂O₃. Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnäsite group. Conservative indices, including TiO₂/Al₂O₃ and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous.     

The SI,a universal language

Abstract

The SI has inherited and developed the fundamental features of the Systéme Métrique: simplicity, universality, and mainly coherence. It has to adapt itself steadily to the new fields and the increasing demand of accuracy, with the constraints of improving its coherence and universality and maintaining the continuity of measurements. The SI cannot ignore such natural units as the day, the turn, and their usual fractions and multiples; they must be tolerated for general use in spite of their incoherence. Such tolerances must be severely restricted. It is the condition for the SI to become and remain a truly universal language common to all fields and all countries. A few simple rules follow that any scientist should keep in mind.     

Ecology of active rock glaciers and surrounding landforms: climate,soil, plants and arthropods

Active rock glaciers are periglacial landforms consisting of coarse debris with interstitial ice or ice‐core. Recent studies showed that such landforms are able to support plant and arthropod life and could act as warm‐stage refugia for cold‐adapted species due to their microclimate features and thermal inertia. However, integrated research comparing active rock glaciers with surrounding landforms to outline their ecological peculiarities is still scarce. We analysed the abiotic (ground surface temperature and humidity, soil physical and chemical parameters) and biotic (plant and arthropod communities) features of two Alpine active rock glaciers with contrasting lithology (silicate and carbonate), and compared them with the surrounding iceless landforms as reference sites (stable slopes and active scree slopes). Our data show remarkable differences between stable slopes and unstable landforms as a whole, while few differences occur between active scree slopes and active rock glaciers: such landforms show similar soil features but different ground surface temperatures (lower on active rock glaciers) and different occurrence of cold‐adapted species (more frequent/abundant on active rock glaciers). Both plant and arthropod species distributions depend mainly on the geographical context as a function of soil pH and on the contrast between stable slopes and unstable landforms as a function of the coarse debris fraction and organic matter content, while the few differences between active scree slopes and active rock glaciers can probably be attributed to microclimate. The role of active rock glaciers as potential warm‐stage refugia for cold‐adapted species is supported by our data; however, at least in the European Alps, their role in this may be less important than that of debris‐covered glaciers, which are able to host cold‐adapted species even below the climatic tree line.     

Effects of saline water irrigation on soil properties in northwest China

Due to the lack of freshwater, highly saline groundwater was the main irrigation source in the last few decades in the Minqin Basin, which is in northwest China. The study evaluates the effects of salt accumulation on the soil physical–chemicals properties. Undisturbed and disturbed soil samples were taken from the experiment site, which was irrigated with saline water at a concentration of 0.8, 2 and 5 g L⁻¹ (coded later as C₀₈, C₂ and C₅). Undisturbed soil samples, at depths of 0–45 and 45–60 cm were taken to determine the water retention curve (WRC). Moreover, in the same place, another set of undisturbed soil samples were taken to determine the porosity and pore-size distribution (PoSD). From the WRC, the water-holding capacity of the soil was estimated. Disturbed soil samples at depths of 0–20, 0–45, 45–60 and 80–100 cm were taken to determine the index of aggregates stability in water (IC). The electrical conductivity of the saturated paste (EC_e) was determined at depths of 0–30, 30–60 and 60–90 cm, during the irrigation season on C₀₈, C₂ and C₅ treatments. The results show that the total porosity and the index of aggregates stability in water decrease with the increasing salinity of irrigation water, and the EC_e increases with the increasing salinity of irrigation water especially in the surface soil. The water-holding capacity (WHC) of soil also increases with the increasing salinity of irrigation water.     

The DRASTIC-Sg model: an extension to the DRASTIC approach for mapping groundwater vulnerability in aquifers subject to differential land subsidence,with application to Mexico City

Mexico City relies on groundwater for most of its domestic supply. Over the years, intensive pumping has led to significant drawdowns and, subsequently, to severe land subsidence. Tensile cracks have also developed or reactivated as a result. All such processes cause damage to urban infrastructure, increasing the risk of spills and favoring contaminant propagation into the aquifer. The effects of ground deformation are frequently ignored in groundwater vulnerability studies, but can be relevant in subsiding cities. This report presents an extension to the DRASTIC methodology, named DRASTIC-Sg, which focuses on evaluating groundwater vulnerability in urban aquifers affected by differential subsidence. A subsidence parameter is developed to represent the ground deformation gradient (Sg), and then used to depict areas where damage risk to urban infrastructure is higher due to fracture propagation. Space-geodetic SqueeSAR data and global positioning system (GPS) validation were used to evaluate subsidence rates and gradients, integrating hydrogeological and geomechanical variables into a GIS environment. Results show that classic DRASTIC approaches may underestimate groundwater vulnerability in settings such as the one at hand. Hence, it is concluded that the Sg parameter is a welcome contribution to develop reliable vulnerability assessments in subsiding basins.     

Radiological characterization of granitoid outcrops and dimension stones of the Variscan Corsica-Sardinia Batholith

This study focuses on the radiological characterization of granitoid outcrops and dimension stones using in situ gamma-ray spectrometry. Extensive measurements were performed on 210 granitoid outcrops of the Corsica-Sardinia Batholith. The large statistical sample allowed us to improve the analysis by considering a log-normal distribution of radioelements and propagating the uncertainties using Monte Carlo method. The activity concentrations of ⁴⁰K, ²²⁶Ra (²³⁸U) and ²³²Th in C-SB area were 1,177 _?304 ⁺⁴⁰⁸ , 60 _?23 ⁺³⁶ and 69 _?25 ⁺³⁸  Bq/kg (at 1σ uncertainty). The median abundance of K, U and Th on the Variscan C-SB was higher than the average values of the upper continental crust and was comparable with Variscan belt. This corresponds to an outdoor absorbed dose rate of 124 _?26 ⁺³³  nGy/h at 1σ uncertainty which is 3σ higher than the population-weighted average absorbed dose rate (60 nGy/h). Seven commercial granites (Rosa Beta, Ghiandone, Giallo San Giacomo, Rosa Cinzia, Grigio Malaga, Bianco Sardo and Grigio Perla) were investigated to characterize their radiological hazard through 147 measurements taken in 73 extractive quarries. All of the commercial granites were categorized as A2 material based on their activity concentration indices, excluding (at the 3σ level) any restriction on their utilization as superficial materials. Rosa Beta, Grigio Malaga, Grigio Perla and Bianco Sardo can also be used as bulk materials as they can be included in the A1 category. In the case of Ghiandone, Giallo San Giacomo and Rosa Cinzia, we are confident of an A1 classification only at the 1σ level.     

Phylogeography of the bluespotted cornetfish,Fistularia commersonii: a predictor of bioinvasion success?

Biological invasions result in huge ecological and economic impacts; therefore, a great amount of effort is dedicated to predicting the potential success of newly established or candidate bioinvaders. Thus far, over 90 species of fish have entered the Mediterranean Sea via the Suez canal, the so‐called Lessepsian bioinvaders. The bluespotted cornetfish, Fistularia commersonii, is remarkable in its ability to disperse within the Mediterranean and has been dubbed ‘the Lessepsian sprinter’. In just a few years, starting in 2000, it expanded over the entire area, from the Suez Canal to Gibraltar. Theoretical predictions correlate the dispersal capabilities of an invader in its native range (using the population genetic metrics, F_st, as a proxy) with its dispersal capability in its invading area (continuous extent of spread, CES). Here, we estimated the population genetic characteristics of Indo‐Pacific native populations of F. commersonii in order to determine if this Lessepsian ‘sprinter’ fits the predictive model of dispersal. Indeed, we found that even in the case of such a very rapid range expansion, the predicted relationship between F_st and CES is fulfilled in F. commersonii.     

浅源强震至浅源特大地震震级M_e的快速测定

提出了根据20°～90°距离范围之内的宽频带远震P波信号快速测定浅源地震能量震级Me的新程序。为了完成这项工作,我们根据地球参考模型AK135Q用数字模拟方法计算了不同周期的频谱振幅衰减函数。根据这些函数,我们校正了远震记录频谱的传播路径效应,计算了地震辐射能量Es和震级Me。我们用累积的P波窗模拟实时或近实时的程序,并用61个浅源地震进行验证。结果表明,我们的方法可在地震发震时刻后的7～15min内迅速可靠地测定出震级Me因此,这一程序适用于快速反应系统的实施。