Euthycarcinoids

The euthycarcinoids are a mysterious group of extinct, possibly amphibious, arthropods. Like many groups of arthropods their affinities remain enigmatic. They comprise 15 species known mainly from the Late Carboniferous Coal Measures of Europe and North America, although they have been found in older rocks in Argentina and Australia. The oldest known euthycarcinoid is Apankura machu, from the Late Cambrian of Argentina, and the youngest is Euthycarcinus kessleri, from the Middle Triassic of France.     

Misplaced trace fossils in unlikely environments

Graphoglyptids are trace fossils that are generally acknowledged to have had a deep-sea origin, displaying complex, nutrient gathering strategies in response to stable environments with low productivity. However, two recently discovered graphoglyptids in the Permian of New Mexico seem to challenge previous assumptions. Rather than in deep-sea sediments, Spirorhaphe azteca and Augerinoichnus helicoidalis were discovered in tidal flat palaeoenvironments, showing that these behavioural patterns are also carried out by animals in tidal settings. Fine sediments of the region are recognized as the key factor in the preservation of these trace fossils. Presence of graphoglyptids in a transitional environment demonstrates that behaviour is not solely defined by depth, but many intricate factors are involved.     

Structural control of scarps in the Rembrandt region of Mercury

Lobate scarps, thought to be the surface expression of large thrust faults, are the most spectacular contractional tectonic features visible on Mercury. Most lobate scarps follow a general and relatively simple pattern, with a roughly arcuate or linear form in plan view, and an asymmetric cross section characterized by a steeply rising scarp face and a gently declining back scarp. In this work, we study two peculiar and complex scarps in the Rembrandt region of Mercury through MESSENGER imagery. On the one hand, the formation of these scarps resulted in the deformation of features such as impact craters, fractures, extensional faults, and volcanic plains, while on the other hand, the deformed features partly influenced the formation of the scarps. Evidence for structural control on the formation of the scarps includes their orientation, segmentation, bifurcation, change in structural trend and dip orientation, and transition into high-relief ridges or wrinkle ridge morphologies in some cases. Thus, these two lobate scarps provide examples of complex geological relations among other features, expanding the recognized richness of mercurian geology. Also, the southern scarp records a complex history of contraction, suggesting that the development of some mercurian lobate scarps may be more complex than usually thought.     

Changes in body condition and fatty acid composition of wild Mediterranean horse mackerel (Trachurus mediterraneus, Steindachner, 1868) associated to sea cage fish farms

Net-cage fish farms attract a great number of wild fishes, altering their behaviour and possibly their physiology. Wild Mediterranean horse mackerel (Trachurus mediterraneus), sampled from populations aggregated around two Mediterranean fish farms and from two natural control populations, were analyzed for differences in body condition, stomach content and fatty acid composition. Pellets used to feed caged fish in both farms were also analyzed to identify their relationship with the fatty acid composition of tissue of wild fish. T. mediterraneus aggregated around the farms throughout the year although large seasonal changes in abundance and biomass occurred. Wild fish aggregated at farms mainly ate food pellets while control fish fed principally on juvenile fish and cephalopods. Wild fish that fed around the cages had a significantly higher body fat content than the control fish (7.30+/-1.8% and 2.36+/-0.7%, respectively). The fatty acid composition also differed between farm-associated and control fish, principally because of the significantly increased levels of linoleic (C18:2omega6) and oleic (C18:1omega9) acids and decreased docosahexaenoic acid (C22:6omega3) in farm-associated fish. The increased condition of wild fish associated with farms could increase the spawning ability of coastal fish populations, if wild fish are protected from fishing while they are present at farms. The fatty acids compositions could also serve as biomarkers to infer the influence of a fish farm on the local fish community, helping to better describe the environmental impact of fish farming.     

Numerical evaluation of multicomponent cation exchange reactive transport in physically and geochemically heterogeneous porous media

Experimental evidence and stochastic studies strongly show that the transport of reactive solutes in porous media is significantly influenced by heterogeneities in hydraulic conductivity, porosity, and sorption parameters. In this paper, we present Monte Carlo numerical simulations of multicomponent reactive transport involving competitive cation exchange reactions in a two-dimensional vertical physically and geochemically heterogeneous medium. Log hydraulic conductivity, log K, and log cation exchange capacity (log CEC) are assumed to be random Gaussian functions with spherical semivariograms. Random realizations of log K and log CEC are used as input data for the numerical simulation of multicomponent reactive transport with CORE^2D, a general purpose reactive transport code. Longitudinal features of the fronts of reactive and conservative species are computed from the temporal and spatial moments of depth-averaged concentrations. Monte Carlo simulations show that: (1) the displacement of reactive fronts increases with increasing variance of log K, while it decreases with the variance of log CEC; (2) second-order spatial moments increase with increasing variances of log K and log CEC; (3) uncertainties in the mean arrival time are largest (smallest) for negatively (positively) correlated log K and Log CEC; (4) cations undergoing competitive cation exchange exhibit different apparent velocities and retardation factors due to both physical and geochemical heterogeneities; and (5) the correlation between log K and log CEC affects significantly apparent cation retardation factors in heterogeneous aquifers.     

A sequential partly iterative approach for multicomponent reactive transport with CORE2D

CORE^2D V4 is a finite element code for modeling partly or fully saturated water flow, heat transport, and multicomponent reactive solute transport under both local chemical equilibrium and kinetic conditions. It can handle coupled microbial processes and geochemical reactions such as acid–base, aqueous complexation, redox, mineral dissolution/precipitation, gas dissolution/exsolution, ion exchange, sorption via linear and nonlinear isotherms, and sorption via surface complexation. Hydraulic parameters may change due to mineral precipitation/dissolution reactions. Coupled transport and chemical equations are solved by using sequential iterative approaches. A sequential partly iterative approach (SPIA) is presented which improves the accuracy of the traditional sequential non-iterative approach (SNIA) and is more efficient than the general sequential iterative approach (SIA). While SNIA leads to a substantial saving of computing time, it introduces numerical errors which are especially large for cation exchange reactions. SPIA improves the efficiency of SIA because the iteration between transport and chemical equations is only performed in nodes with a large mass transfer between solid and liquid phases. The efficiency and accuracy of SPIA are compared to those of SIA and SNIA using synthetic examples and a case study of reactive transport through the Llobregat Delta aquitard in Spain. SPIA is found to be as accurate as SIA while requiring significantly less CPU time. In addition, SPIA is much more accurate than SNIA with only a minor increase in computing time. A further enhancement of the efficiency of SPIA is achieved by improving the efficiency of the Newton–Raphson method used for solving chemical equations. Such an improvement is obtained by working with increments of log concentrations and ignoring the terms of the Jacobian matrix containing derivatives of activity coefficients. A proof is given for the symmetry and non-singularity of the Jacobian matrix. Numerical analyses performed with synthetic examples confirm that these modifications improve the efficiency and convergence of the iterative algorithm. Changbing Yang is now at The University of Texas at Austin, USA.     

Thermo-optical detection of defects and decarbonation in natural smithsonite

Natural hydrothermal ZnCO₃ crystal aggregates are nominally anhydrous phases with interfacial water, with substitutional divalent cations and decarbonation c. 300°C. All these common features must be involved during the experimental heating of a thermoluminescence (TL) glow curve up to 500°C: dehydration–dehydroxylation, phase transition and ion transition of point defects in Zn²⁺ positions. A representative specimen of natural smithsonite was analysed by X-ray fluorescence spectrometry, field emission scanning electron microscopy (FESEM) with a chemical probe of energy dispersive spectrometer, high temperature in situ X-ray diffraction, differential scanning calorimetry, differential thermal analyses coupled to thermogravimetry, TL, radioluminescence and high resolution spectra thermoluminescence (3DTL), to gain an overview of the spectra emission and defects linkages modified by heating from room temperature up to 500°C. The ZnCO₃ specimen contains minor amounts of Ca, Cu, Cr, Cd, Pb, Ce, Co, Ni, Mn and Fe. Under FESEM, it displays CaCO₃ clusters and oscillatory zoning distribution with lamellae ranging from Ca_0.11Zn_0.89 to Ca_0.19Zn_0.81. The analytical results suggest assignments of defects and processes to measured 3DTL emission bands, as follows: (1) peak at ~260°C, ~360 nm bonds, breaking during the thermal decarbonation process; (2) peak ~120°C, ~340 nm: non-bridging oxygen centres associated to a complex dehydration–dehydroxylation process and (3) peak at ~170°C, ~650 nm, crystal field effects on the thermoluminescence of Mn²⁺ centres and associated transitional elements in the ZnCO₃ phase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

New Plateau de Bure observations of M 1–92; unveiling the core

M 1–92 is a very well studied bipolar pPN that can be considered an archetype of this type of sources; it shows a clear axial symmetry, along with the kinematics characteristic of this class of envelopes around post-AGB stars. We performed sub-arcsecond resolution observations of the J=2–1 rotational line of ¹³CO in M 1–92 with the new extended configurations of the IRAM Plateau de Bure interferometer, for studying the morphology and velocity field of the molecular gas better in the nebula, particularly in its central parts. We found that the equatorial structure dividing the two lobes is a thin flat disk, which expands radially with a velocity proportional to the distance to the central stellar system. The kinetic age of this equatorial flow is very similar to that measured in the two lobes, suggesting that the whole structure was formed as a result of a single event some 1200 yr ago, after which the nebula reached an expansion velocity field with axial symmetry. The small widths and velocity dispersion in the gas forming the lobe walls confirm that the acceleration responsible for the nebular shape could not last more than 100–120 yr. In view of the similarity to η Car, we speculate on the possibility that the whole nebula was formed as a result of a magneto-rotational explosion in a common-envelope system. The study of the possible importance of this mechanism in the context of global PNe and pPNe reshaping should be one on the fields in which future ALMA observations will make a crucial contribution. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).     

Geochemical Characterization of Magnetite and Geological Setting of the Iron Oxide ± Iron Silicate ± Iron Carbonate Rich Pb–Zn Sulfides from the La Unión and Mazarrón Stratabound Deposits (SE Spain)

From a mineralogical point of view the La Unión ore field (SE Spain) can be regarded as an oddity as some of its hydrothermal, stratabound type deposits display an extremely unusual paragenesis comprising magnetite ± greenalite ± minnesotaite ± siderite and galena ± sphalerite (IOSC – LZS). Recent mineralogical studies have shown that this paragenesis is also present at the neighboring Mazarrón ore field. These ore fields share a similar geologic setting, involving metamorphic and sedimentary rocks (Paleozoic s.l. to Permian) hosting late Miocene high‐K calc‐alkaline volcanic and subvolcanic rocks. The latter have andesitic to dacitic composition, and triggered hydrothermal activity and ore deposition. This study discusses the detailed mineral chemistry of magnetite samples from Mazarrón and La Unión and provides some hints for the origin of the IOSC – LZS paragenesis. We performed electron microprobe (EPMA) analyses in magnetite samples from La Unión and Mazarrón to determine the contents of minor and trace elements (Zn, Ni, Mn, Cr, V, K, Ca, Ti, Al, Si, Mg). Given that some results fell below the detection limit for the EPMA instrumental conditions we used robust regression on order statistics (robust ROS), with the NADA package in R to deal with these data sets. The Ca + Al + Mn contents in magnetites from San Cristóbal and Emilia are equivalent to the mean contents of those of IOCG, Kiruna, BIF, Cu porphyry, skarn, VMS, hydrothermal and clastic Pb–Zn deposits, but they are low in Ti + V and Ni + Cr. The principal components analysis indicates that Zn, Ni, Cr, V, K, Ca, Ti, and Mg are roughly collinear, therefore correlated, being also independent from Fe. Besides, the function discriminant analysis of data shows that the magnetites from Emilia and San Cristóbal cluster in differentiated groups, thus probably reflecting some differences related to the distance to the magmatic source that triggered the hydrothermal system: proximal in the case of San Cristóbal and distal in Emilia.     

Removal of arsenic and iron from mine-tailing leachate using chitosan hydrogels synthesized by gamma radiation

Mine residue and leachate were sampled from an acid mine drainage site near Arroyo San Pedro, which is one of the oldest abandoned mine districts in San Luis Potosi, Mexico, and characterized by X-ray diffraction and inductively coupled plasma-optical emission spectroscopy, confirming the presence of Fe, As, and SO₄ ^2?. To address this problem, chitosan network (net-CS) and chitosan network-N-vinylcaprolactam/N–N-dimethylacrylamide (net-CS)-g-NVCL/DMAAm hydrogels were synthesized and used as adsorbents of the different ions present in the aforementioned leachate by batch equilibrium procedure. Kinetics, isotherms, and ions dissolved in leachate were evaluated. The gels showed the highest adsorption capacity for As and Fe ions. The adsorption capacity of the net-CS hydrogels for As (V) and Fe(III) was 0.786 and 76.85 mg/g, respectively, attained after 50 h. The surface of the hydrogels was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy, before and after the adsorption process, where the presence of a bond between the hydrogels and heavy metals ions, which is commonly observed in organic groups, was observed. In addition, Freundlich and Langmuir adsorption isotherms constants were determined for the As and Fe ions, and it was found that the Freundlich isotherm, with a first-order pseudo model, better fitted the adsorption process, indicating heterogeneous sorption, and the retention process occurred by chemisorption. The results from the Geochemist´s Workbench (GWB) software program revealed that arsenates, such as H₃AsO₄, H₂AsO₄ ^?, as well as Fe⁺⁺, FeSO₄(aq) and FeOH⁺ were the common aqueous species found in the leachate at pH = 2.9.