Rare Earth and Metal Geochemistry of Land and Submarine Phosphorites in the Baja California Peninsula,Mexico

The geochemical composition of phosphorites and phosphatic sediments in the Baja California peninsula is studied and used to assess the environment in which phosphogenesis took place. The deposits are classified in three groups: (1) stratified phosphorites, (2) phosphatic sandy sediments from beaches and dunes, and (3) submarine sediments. Some of the elements that might have substituted Ca and PO₄ during francolite mineralization were studied by means of ICP-AES. Significant differences are seen in the concentration of these metals (e.g., Cr = 72-406 μg g^?1 and V = 17-198 μg g^?1), indicating that their concentration is not only controlled by the P₂O₅ concentration, but also by paleo-environmental conditions existing during francolite precipitation. Shale normalized REE patterns suggest two main environments of formation: (1) a strong negative Ce anomaly (< ? 0.3) and La enrichment (La/Nd ≥ 1) enrichment, suggesting well oxygenated shelf environments and probably lower light REE weathering, and (2) a weak negative Ce anomaly (> ? 0.3) and La depletion (La/Nd ≤ 1) suggesting shallower waters or restricted circulation and probably LREE weathering.     

Stratigraphy and tectonics of a time-transgressive ophiolite obduction onto the eastern margin of the Pelagonian platform from Late Bathonian until Valanginian time,exemplified in northern Evvoia,Greece

The obduction of an ophiolite sheet onto the eastern Pelagonian carbonate platform complex of the Hellenides began during the Late Bathonian and ended with the final emplacement of the ophiolite during Valanginian time. The early stages of obduction caused subaerial exposure of the platform, recorded by an unconformity of Callovian age, which is marked by laterites overlying folded and faulted, karstic substrates. The laterites have distinct ophiolitic geochemical signatures, indicating that emergent ophiolite had been undergoing lateritic weathering. This unconformity coincides with widespread western Tethyan, Callovian gaps, indicating that the obduction in the Hellenides was probably related to far-reaching plate tectonic processes. Resumed gravitational pull and rollback of the subducted, oceanic leading edge of the temporarily exposed ophiolite. Platform drowning continued into Tithonian–Valanginian time, documented initially by reefal carbonates and then by below-CCD, carbonate-free radiolarian cherts and shales. Subsequently, siliciclastic turbidites, which apparently originated from uplifted Variscan basement, were deposited together with and over the radiolarite as the ophiolite nappe sheet advanced. The nappe substrate underwent tectonic deformations of varying intensity, while polymictic mélange and syntectonic sedimentary debris accreted beneath the ophiolite and at the nappe front. The provenience of the ophiolite nappe complexes of northern Evvoia most probably has to be looked for in the Vardar ocean.     

Geophysical exploration on the subsurface geology of La Garrotxa monogenetic volcanic field (NE Iberian Peninsula)

We applied self-potential (SP) and electrical resistivity tomography (ERT) to the exploration of the uppermost part of the substrate geology and shallow structure of La Garrotxa monogenetic volcanic field, part of the European Neogene–Quaternary volcanic province. The aim of the study was to improve knowledge of the shallowest part of the feeding system of these monogenetic volcanoes and of its relationship with the subsurface geology. This study complements previous geophysical studies carried out at a less detailed scale and aimed at identifying deeper structures, and together will constitute the basis to establish volcanic susceptibility in La Garrotxa. SP study complemented previous smaller-scale studies and targeted key areas where ERT could be conducted. The main new results include the generation of resistivity models identifying dykes and faults associated with several monogenetic cones. The combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to NNW–SSE and accessorily by NNE–SSW Neogene extensional fissures and faults and concretely show the associated magmatic intrusions. These structures coincide with the deeper ones identified in previous studies, and show that previous Alpine tectonic structures played no apparent role in controlling the loci of this volcanism. Moreover, the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area are controlled by shallow stratigraphical, structural and hydrogeological differences underneath these monogenetic volcanoes.     

The Scattered Disk Population and the Oort Cloud

The trans-Neptunian belt has been subject to a strong depletion that has reduced its primordial population by a factor of one hundred over the solar system's age. One by-product of such a depletion process is the existence of a scattered disk population in transit from the belt to other places, such as the Jupiter zone, the Oort cloud or interstellar space. We have integrated the orbits of the scattered disk objects (SDOs) so far discovered by 2500 Myr to study their dynamical time scales and the probability of falling in each of the end states mentioned above, paying special attention to their contribution to the Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr and that about one third of the SDOs end up in the Oort cloud.     

Un nouveau gisement de granite orbiculaire dans le Massif Central français: le granite du Signal de Randon (Lozère)

This orbicular granite contains ovoïds of an exceptional composition, comprising a core of biotite, surrounded by an envelope of plagioclase, enclosed in turn by an envelope of potassium feldspar. The latter also occurs as isolated idiomorphic megacristals between the ovoïds.Because of the spectacularly clear mineralogical relationships of the rock, it is possible to work out the order of crystallization of the minerals, the magmatic differentiation of syenitic orbicules and that of the leucogranitic groundmass with an aplito-pegmatitic texture.A magmatic process is proposed to explain the origin of the rock.

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Les déterminations de l'indice de triclinicité des feldspaths potassiques ont été effectuées par Yves Blanc, Clermont-Ferrand (diffractométrie X, d'après G. Sabatier, 1963).     

Why chromatic imaging matters

During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u ? v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.     

Detection of DNA damage in mussels and sea urchins exposed to crude oil using comet assay

The single-cell microgel electrophoresis assay or the comet assay was used to evaluate DNA damage of dispersed crude oil on sea urchins (Strongylocentrotus droebachiensis) and mussels (Mytilus edulis L.). Sea urchins were exposed to 0.06 and 0.25 mg/L dispersed crude oil in a continuous flow system, while the mussels were exposed to 0.015, 0.06 and 0.25 mg/L dispersed crude oil. Sea urchin coelomocytes and mussel haemocytes were sampled after 4 and 5 weeks exposure, respectively. In the sea urchin coelomocytes, there was a significant concentration-related increase in the percentage of DNA in comet tail. In mussel haemocytes, there was a significantly higher percentage of DNA in comet tail for all treatments compared to the control. The responses were concentration-related up to 0.06 mg/L oil. The two highest exposure concentrations of mussels were not significantly different from each other. These results indicate that the comet assay can be used for biomonitoring of DNA damage in marine invertebrates following oil contamination.     

Social networks and healthy cities: spreading good practices based on a spanish case study

The city of Vitoria‐Gasteiz in Spain is considered a “healthy city” and has implemented sustainable actions to increase the mobility of its healthcare professionals. The objectives of this study are firstly to account for the use of bicycles at work as a strategy for a healthy city and secondly to propose a conceptual framework for analyzing this network and its capacity to spread their practices The paradigm proposed is that of social networks, within which sharing between contacts is explained by means of two models: the “threshold model” and “opinion leaders”.     

Natural Arsenic Attenuation via Metal Arsenate Precipitation in Soils Contaminated with Metallurgical Wastes: I. Wet Chemical and Thermodynamic Evidences

Arsenic from natural and anthropogenic sources is a worldwide contaminant of aqueous environments, such as groundwater and soils. The present investigation was performed on Mexican soils contaminated with residues from metallurgical processes that have shown a natural As attenuation. Experimental aqueous arsenic extractions in these were successfully simulated for almost half of the soil samples using a database updated for all known metal arsenate formation constants, revealing the predominance of solubility-controlled As mobility via Pb, mixed Pb–Cu, and Ca arsenate solid formation. The relatively low total Fe/As ratios (2–13 w/w) present in the soils studied, together with the high and equivalent contents of As, Pb, and Cu in these, favor the precipitation process over As(V) adsorption to Fe oxides, despite a 2% average Fe content in the soils studied. Under these conditions bicarbonate was found to be a highly unsuitable extractant due to its indirect As release from the solid arsenates, via heavy metal carbonate precipitation processes.     

Response of suspended sediment particle size distributions to changes in water chemistry at an Andean mountain stream confluence receiving arsenic rich acid drainage

Acid drainage is an important water quality issue in Andean watersheds, affecting the sustainability of urban, agricultural, and industrial activities. Mixing zones receiving acid drainage are critical sites where changes in pH and chemical environment promote the formation and dissolution of iron and aluminum oxy/hydroxides. These particles can significantly change the speciation of toxic metals and metalloids throughout drainage networks via sorption, desorption, and settling processes. However, little is known about the behavior of particle size distributions (PSDs) in streams affected by acid drainage and their relationship to metal speciation. This work studied: (a) the PSDs for a wide range of mixing ratios found at a fluvial confluence affected by acid drainage, and (b) the response of PSDs and arsenic speciation to environmental changes found when the particles approach complete mixing conditions. The confluence between the Azufre River (pH ~ 2, high concentration of dissolved metals) and Caracarani River (pH = 8.6, low concentration of dissolved metals) was used as a representative model for study. Field measurements show a bimodal PSD with modal diameters of ~50 and 300 μm. At shorter distances from the junction, the smaller modes with smaller particle volumes were dominant across the stream cross‐sections. A systematic shift towards larger particle sizes and larger particle volumes occurred downstream. The analysis of laboratory PSDs for Azufre/Caracarani mixing ratios between 0.01 and 0.5 (pH from 6.2 to 2.3) showed a bimodal trend with ~15 and 50 μm characteristic diameters; larger particles formed at pH>4. When particle suspensions were transferred in laboratory experiments from very low pH to full mixing conditions (pH ~ 2.8 and mixing ratio ~ 0.25) particle sizes varied, and the dissolved arsenic concentration decreased. The observed reaction kinetics were slow compared to the time scale of advective transport, creating opportunities for engineered controls for arsenic. This work contributes to a better understanding of the chemical‐hydrodynamic interactions in watersheds affected by mining, and identifying opportunities to improve water quality at points of use.