Large-scale slope failure involving Triassic and Middle Miocene salt and shale in the Gulf of Cádiz (Atlantic Iberian Margin)

Sheets of salt and ductile shale advancing beyond the thrust front of the Gibraltar Arc (Iberian–Moroccan Atlantic continental margin) triggered downslope movements of huge allochthonous masses. These allochthons represent the Cádiz Nappe, which detached from the Gibraltar Arc along low‐angle normal faults and migrated downslope from the Iberian and Moroccan continental margins towards the Atlantic Ocean. Extensional tectonics initiated upslope salt withdrawal and downslope diapirism during large‐scale westward mass wasting from the shelf and upper slope. Low‐angle salt and shale detachments bound by lateral ramps link extensional structures in the shelf to folding, thrusting and sheets of salt and shale in the Gulf of Cádiz. From backstripping analyses carried out on the depocentres of the growth‐fault‐related basins on the shelf, we infer two episodes of rapid subsidence related to extensional collapses; these were from Late Tortonian to Late Messinian (200–400 m Myr^?1) and from Early Pliocene to Late Pliocene (100–150 m Myr^?1). The extensional events that induced salt movements also affected basement deformation and were, probably, associated with the westward advance of frontal thrusts of the Gibraltar Arc as a result of the convergence between Africa and Eurasia. The complexities of salt and/or shale tectonics in the Gulf of Cádiz result from a combination of the deformations seen at convergent and passive continental margins.     

Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater,Egypt

Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz‐rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high‐pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s^?1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.     

Frequency of hyperbolic and interstellar meteoroids

Hyperbolic meteor orbits from the catalog of 64,650 meteors observed by the multistation video meteor network located in Japan (SonotaCo 2009) have been investigated with the aim of determining the relation between the frequency of hyperbolic and interstellar meteors. The proportion of hyperbolic meteors in the data decreased significantly (from 11.58% to 3.28%) after a selection of quality orbits, which shows its dependence on the quality of observations. Initially, the hyperbolic orbits were searched for meteors unbound due to planetary perturbation. It was determined that 22 meteors from the 7489 hyperbolic orbits in the catalog (and 2 from the selection of the orbits with the highest quality) had had a close encounter with a planet, none of which, however, produced essential changes in their orbits. Similarly, the fraction of hyperbolic orbits in the data, which could be hyperbolic by reason of a meteor's interstellar origin, was determined to be at most 3.9 × 10^?2. From the statistical point of view, the vast majority of hyperbolic meteors in the database have definitely been caused by inaccuracy in the velocity determination. This fact does not necessarily assume great measurement errors, since, especially near the parabolic limit, a small error in the value of the heliocentric velocity of a meteor can create an artificial hyperbolic orbit that does not really exist. The results show that the remaining 96% of meteoroids with apparent hyperbolic orbits belong to the solar system meteoroid population. This is also supported by their high abundance (about 50%) among the meteor showers.     

Effects of capillary reflection in the performance of the collimator of the Large Area Detector on board LOFT

The Large Observatory For X-ray Timing (LOFT) is one of the candidate missions selected by the European Space Agency for an initial assessment phase in the Cosmic Vision programme. It is proposed for the M3 launch slot and has broad scientific goals related to fast timing of astrophysical X-ray sources. LOFT will carry the Large Area Detector (LAD), as one of the two core science instruments, necessary to achieve the challenging objectives of the project. LAD is a collimated detector working in the energy range 2-50 keV with an effective area of approximately 10 m ²at 8 keV. The instrument comprises an array of modules located on deployable panels. Lead-glass microchannel plate (MCP) collimators are located in front of the large-area Silicon Drift Detectors (SDD) to reduce the background contamination from off-axis resolved point sources and from the diffuse X-ray background. The inner walls of the microchannel plate pores reflect grazing incidence X-ray photons with a probability that depends on energy. In this paper, we present a study performed with an ad-hoc simulator of the effects of this capillary reflectivity on the overall instrument performance. The reflectivity is derived from a limited set of laboratory measurements, used to constrain the model. The measurements were taken using a prototype collimator whose thickness is similar to that adopted in the current baseline design proposed for the LAD. We find that the experimentally measured level of reflectivity of the pore inner walls enhances the off-axis transmission at low energies, producing an almost flat-top response. The resulting background increase due to the diffuse cosmic X-ray emission and sources within the field of view does not degrade the instrument sensitivity.     

Is there any long-term memory effect in the tropical cyclones?

The investigation of the intrinsic properties of the annual tropical cyclone count over Atlantic, during 1870–2006, is herewith attempted. The motivation behind this exploration is to contribute to the current understanding about the dynamics of these disastrous events, as tropical cyclones create destructive impacts for people living around tropical areas. The analytical tool used is the detrended fluctuation analysis, and the exponent obtained reveals that the time series of the annual tropical cyclone count over Atlantic obeys the classical random walk (white noise). In other words, the number of tropical cyclones seems to exhibit neither persistent nor antipersistent behavior. The reliability of the lack of scaling dependence in the time series of the annual tropical cyclone count is confirmed, by applying error bounds statistics and studying the decay of the autocorrelation function (i.e., not rejected exponential decay) and the variability of local slopes (i.e., lack of constancy in a sufficient range). In addition, the fact that the series used is fractional Gaussian noise depicts that the results obtained are reliable, despite the fact that the available data set is still limited. The indication of a nearly white noise signal in the tropical cyclone count fluctuations does not suggest that the climate change phenomenon does not exist.     

Impact of climate variability on summer fires in a Mediterranean environment (northeastern Iberian Peninsula)

We analyse the impact of climate interannual variability on summer forest fires in Catalonia (northeastern Iberian Peninsula). The study period covers 25 years, from 1983 to 2007. During this period more than 16000 fire events were recorded and the total burned area was more than 240 kha, i.e. around 7.5% of whole Catalonia. We show that the interannual variability of summer fires is significantly correlated with summer precipitation and summer maximum temperature. In addition, fires are significantly related to antecedent climate conditions, showing positive correlation with lagged precipitation and negative correlation with lagged temperatures, both with a time lag of two years, and negative correlation with the minimum temperature in the spring of the same year. The interaction between antecedent climate conditions and fire variability highlights the importance of climate not only in regulating fuel flammability, but also fuel structure. On the basis of these results, we discuss a simple regression model that explains up to 76% of the variance of the Burned Area and up to 91% of the variance of the number of fires. This simple regression model produces reliable out-of-sample predictions of the impact of climate variability on summer forest fires and it could be used to estimate fire response to different climate change scenarios, assuming that climate-vegetation-humans-fire interactions will not change significantly.     

Origin of atoll garnet in schists from the Alpuj��rride Complex (Central zone of the Betic Cordillera, Spain): Implications on the P-T evolution

Atoll-shaped and normal garnets from schists of the Betic Cordillera (Spain) were studied by electron microprobe, scanning electron microscopy and microstructural electron backscattered scanning diffraction (EBSD). Medium-grade schists contain a textural variety of atoll garnets, characterized by the presence of muscovite, annite, and quartz as main ??core?? phases. Zoning patterns, EBSD analyses and themobarometric data indicate that the micaceous intergrowths formed in most cases through breakdown of a first garnet generation, with orientation of micas being controlled by garnet (c*_mica//[111]*_Grt and c*_mica//[110]*_Grt as main crystallographic relationships). Rings formed from multiple nucleation and coalescence, with orientation being controlled, in some cases, by the relics of the initial garnet and more generally by mica orientation. P-T estimates indicate that the first stage of garnet growth occurred at relatively high P (9?C12?kbar/500?C550°C) whereas the second metamorphic stage occurred at lower P and slightly higher T conditions (5?C7?kbar/500?C600°C).     

Interacting Effect of pH,Phosphate and Time on the Release of Arsenic from Polluted River Sediments (Anllóns River,Spain)

The interacting effect of pH, phosphate and time on the release of arsenic (As) from As-rich river bed sediments was studied. Arsenic release edges and kinetic release experiments (pH range 3–10), in the absence and presence of phosphate, coupled with sequential extraction procedures, SEM/EDX analyses and geochemical calculations, were carried out to evaluate As remobilisation and to elucidate the mechanisms involved. The results showed that As release underwent pronounced kinetic effects, which were strongly influenced by pH and phosphate. Remobilisation of As after 24 h was low (between ~1 and 5%) and varied slightly with pH, whereas alkaline conditions generally promoted As remobilisation after 168 h, with up to 12–21% of total As released. The results showed that depending on the pH and sediment considered, the release of As increased dramatically after ~48–72 h, suggesting that different processes are involved at different reaction periods. The addition of phosphate (1 mM) increased both the amount of As released (between 2 and 8 times) and the rate of As release from the sediments within the entire pH range (3–10) and period (168 h) studied. Moreover, in some cases, it also affected the shape of the As release edges and kinetic profiles. The similarities in the release profiles and the positive correlations between As and some sediment components, especially Fe and Al hydroxides, and organic matter—which appears to play a key role at high pH—suggest that As release from the studied sediments may be associated with solid phase dissolution processes under both acid and alkaline pH, whereas desorption plays a key role in the short term and at natural pH conditions, especially in the presence of phosphate, which acts as an As-displacing ligand. Evaluation of As mobility based on short-time leaching experiments may seriously underestimate the mobilisation of As from sediments.     

3D-electrical resistivity tomography monitoring of salt transport in homogeneous and layered soil samples

Monitoring transport of dissolved substances in soil deposits is particularly relevant where safety is concerned, as in the case of geo-environmental barriers. Geophysical methods are very appealing, since they cover a wide domain, localising possible preferential flow paths and providing reliable links between geophysical quantities and hydrological variables. This paper describes a 3D laboratory application of electrical resistivity tomography (ERT) used to monitor solute transport processes. Dissolution and transport tests on both homogeneous and heterogeneous samples were conducted in an instrumented oedometer cell. ERT was used to create maps of electrical conductivity of the monitored domain at different time intervals and to estimate concentration variations within the interstitial fluid. Comparisons with finite element simulations of the transport processes were performed to check the consistency of the results. Tests confirmed that the technique can monitor salt transport, infer the hydro-chemical behaviour of heterogeneous geomaterials and evaluate the performances of clay barriers.     

Structural and geochemical alterations in the Mg calcite bryozoan Myriapora truncata under elevated seawater pCO2 simulating ocean acidification

The possible effects of ocean acidification on the calcareous skeleton of the Mediterranean bryozoan Myriapora truncata (Pallas, 1766) were studied by transplanting live and dead colonies into an area of natural volcanic CO₂ vents at Ischia (Gulf of Naples, Tyrrhenian Sea), Italy. Morphology and geochemistry were compared between colonies from normal (mean pH = 8.07, min. pH 7.95), below‐normal (mean pH 7.66, min. pH 7.32) and acidic (mean pH 7.43, min. pH 6.83) conditions after colonies had been exposed in situ for 45 and 128 days. Both distal (juvenile) and proximal (adult) parts of the branches were investigated. Skeletons of live colonies in acidic pH site after 45 days of exposure were less corroded than those of dead colonies, suggesting that the organic tissues enveloping the skeleton play a protective role. Colonies remained alive at the below‐normal and acidic pH sites during the 45‐day experiment but corrosion was very striking after 128 days, with colonies from the acidic site showing significant loss of skeleton. Compared to the control, these colonies also had lower levels of Mg (mean 8 versus 9.5 wt% Mg) within their skeletons. Electron microprobe mapping showed Mg to be higher in the outer layers of the skeletal walls in colonies from the normal pH site. Corrosion of outer layers of the walls probably explains the lower Mg level found in colonies exposed to acidic conditions. As solubility of calcite increases with Mg content, the enrichment of Mg in outer layers of the skeleton should enhance the vulnerability of Myriapora truncata to dissolution. These findings raise concerns over the survival of bryozoans with Mg calcite skeletons in the face of predicted decreases in oceanic pH levels.