ALBERT

Description: 〈span〉〈div〉Abstract〈/div〉We have investigated a locality very well known to mineral collectors, the Yates U-Th prospect near Otter Lake, Québec. There, dikes of orange to pink calcite enclose euhedral prisms of fluorapatite, locally aligned. Early investigators pointed out the importance of micro-inclusions in the prisms. We describe and image the micro-inclusions in two polished sections of fluorapatite prisms, one of them with a millimetric globule of orange calcite similar to that in the matrix. We interpret the globule to have been an inclusion of melt trapped during growth. Micro-globules disseminated in the fluorapatite are interpreted to have crystallized 〈span〉in situ〈/span〉 from aliquots of the boundary-layer melt enriched in constituents rejected by the fluorapatite; the micro-globules contain a complex jigsawed assemblage of carbonate, silicate, and sulfate minerals. Early minerals to crystallize are commonly partly dissolved and partly replaced by lower-temperature phases. Such jigsawed assemblages seem to be absent in the carbonate matrix sampled away from the fluorapatite prisms. The pressure and temperature attained at the Rigolet stage of the Grenville collisional orogeny were conducive to the anatexis of marble in the presence of H〈sub〉2〈/sub〉O. The carbonate melt is considered to have become silicocarbonatitic by assimilation of the enclosing gneisses, which were also close to their melting point. Degassing was important, and the melt froze quickly. The evidence points to a magmatic origin for the carbonate dikes and the associated clinopyroxenite, rather than a skarn-related association.〈/span〉

Description: A scimitar-toothed cat ( Homotherium serum ) and stag moose ( Cervalces sp.) are described from Tyson Spring Cave, Fillmore County, Minnesota. These specimens represent the first records of both species in the state, and the first record for H. serum in the Great Lakes region. Although the Cervalces specimen remains undated, it shares features with pre-Wisconsin specimens from the eastern Great Plains. The H. serum individual dates to c.  26.9 ka, when the Wisconsin ice margin was less than 60 km away. Genetic analyses support the identity of the Homotherium specimen as conspecific with Homotherium serum found in older Beringian deposits, as well as both the early divergence of tribes Homotherini and Smilodontini within Machairodontinae and the early divergence of this Machairodontinae from the lineage that produced extant cats.

Description: Valiña-Azúmara es un yacimiento filoniano de Au-As (Ag-Pb-Zn-Cu-Sb) situado en la provincia de Lugo (NO España), que fue explotado por arsénico a principios del siglo XX. La mineralización se encuentra encajada en un cabalgamiento Varisco de dirección de buzamiento N247-261°E y en fracturas tardivariscas de dirección N-S y NE-SO que cortan a filitas negras de edad Cámbrica. En menor medida la mineralización también se encuentra diseminada en el encajante, en finas salbandas levemente sericitizadas y silicificadas. La mineralización se divide en dos etapas hipogénicas. La primera está constituida por cuarzo, calcita, rutilo, sericita, arsenopirita y pirita. En base a su composición y textura, se diferencian dos tipos de pirita, Py-I y Py II. La Py-II suele encontrarse recrecida sobre la Py I, formando bandas poligonales. Esta pirita está enriquecida en As (≤1,7% en peso) y contiene trazas de otros metales como Te, Zn, Cu, Bi, Sb y Au. Los tramos mineralizados de sondeo del yacimiento presentan correlación geoquímica entre los elementos Au y As, debido a que el Au se halla en forma de oro refractario dentro de los cristales de pirita arsenical (Py-II), los cuales llegan a presentar concentraciones en Au de hasta 176 ppm. La relación Au/As de la Py-II sugiere que el oro se encuentra en forma de Au +1 , en solución sólida dentro de la estructura cristalina del mineral. La segunda etapa de mineralización está enriquecida en Ag-Pb-Zn-Cu-Sb y consiste en cuarzo, calcita, clorita, esfalerita, jamesonita, cobres grises (tetraedrita argentífera y freibergita), calcopirita, pirrotina y galena. Esta etapa se encuentra rellenando fracturas y cavidades intersticiales en los minerales de la etapa anterior, reemplazándolos en parte. Los principales minerales portadores de Ag son los cobres grises, con contenidos que varían entre 13,7 y 23,9% en peso. En la parte más superficial del yacimiento, la alteración supergénica de la mena primaria dio como resultado la formación de óxidos e hidróxidos de hierro, escorodita y anglesita.

Description: A numerical model indicates that rough topography at the ends of the 100 km long western Strait of Juan de Fuca (WJdF) creates large-scale asymmetries in the tidal flow which complicate the subtidal dynamics in WJdF proper. In large regions, surface height increases and density decreases toward the ocean (as confirmed by hydrographic data). The Coriolis, advection, and pressure gradient momentum terms are large and variable, but their sum, CAP, remains small and steady. CAP drives the time-mean subtidal inflow against bottom friction, while the outflow is lightly damped. Previous studies which found large internal stresses may have been misled by the unexpected complexity of the subtidal dynamics. The model finds that about half of the time-mean subtidal transport is due to tidal rectification alone, while the density-driven component is proportional to the salinity difference from the ocean to the interior. Combining these results with measured salinity data suggests that the seasonal variation of the time-mean subtidal transport in WJdF is relatively small. This does not imply that the same is true upstream.

Description: Clay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p'-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p'-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked with p,p'-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30{degrees}C. Results revealed a progressive decrease in p,p'-DDT and increase in p,p'-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

Description: Crystal Growth & Design DOI: 10.1021/cg5016934

Description: Detailed textural and mineralogical investigations carried out in mineralized veins of the New Caledonian peridotites reveal three major periods of infilling and alteration closely linked to post-obduction tectonic activity. The first two periods of infillings are related to the alteration of hydrothermal serpentines, mostly found in the thick serpentine network of the peridotites, into fine-grained serpentine-like residues and newly formed talc-like minerals of weak but variable swelling capacity. The alteration of serpentine into talc-like minerals is limited during the first period of infilling and almost completed during the second one. In some fault zones of the New Caledonian peridotites, talc-like minerals are replaced by sepiolite. Such alterations are reported in both the Ni-free and Ni-rich zones of the infillings ( i.e. in the white ‘deweylite’ and greenish ‘garnierite’ of the fault zones, respectively). They led to the individualization of the hydrous Mg/Ni silicate ore, which is nowadays found in fractures of the saprock and saprolite units of thick lateritic profiles. The third and last period of infilling is assigned to the accumulation of silica and crystallization of quartz. This succession of clay minerals (serpentine-like and talc-like minerals, sepiolite) and quartz in the infillings is interpreted as the result of sequential exportation of Mg and redistribution of Ni along the reactivated faults, generating periods of increasing Si activity in solutions. In this paragenetic model, the meteoric water infiltrating repeatedly the permeable network created by post-obduction tectonic activity would have interacted with a low-temperature hydrothermal field following the exhumation and cooling of the ophiolite nappe. In the less permeable parts of the fault network, restricted leaching conditions would have generated greater alkalinity in solutions and therefore favored the crystallization of sepiolite instead of finely divided talc-like minerals.

Description: Throughout the 50 years of the Quarterly Journal of Engineering Geology and Hydrogeology papers have been published on case studies, site characterization and material geotechnical properties that have been influenced by the climatic and geomorphological environments experienced during the Quaternary. This period of geological time has left a significant legacy for ground engineering and construction projects with a complexity of ground conditions whose interpretation and understanding are crucial for the success of any such schemes. This review presents key papers that mainly focus on the effects of cold climates, both glacial and periglacial, developed during this time. Advances in landsystem description and ground model development published in the journal for these terrains are discussed.

Description: In recent years, the application of time-domain adjoint methods to improve large, complex underground tomographic models at the regional scale has led to new challenges for the numerical simulation of forward or adjoint elastic wave propagation problems. An important challenge is to design an efficient infinite-domain truncation method suitable for accurately truncating an infinite domain governed by the second-order elastic wave equation written in displacement and computed based on a finite-element (FE) method. In this paper, we make several steps towards this goal. First, we make the 2-D convolution formulation of the complex-frequency-shifted unsplit-field perfectly matched layer (CFS-UPML) derived in previous work more flexible by providing a new treatment to analytically remove singular parameters in the formulation. We also extend this new formulation to 3-D. Furthermore, we derive the auxiliary differential equation (ADE) form of CFS-UPML, which allows for extension to higher order time schemes and is easier to implement. Secondly, we rigorously derive the CFS-UPML formulation for time-domain adjoint elastic wave problems, which to our knowledge has never been done before. Thirdly, in the case of classical low-order FE methods, we show numerically that we achieve long-time stability for both forward and adjoint problems both for the convolution and the ADE formulations. In the case of higher order Legendre spectral-element methods, we show that weak numerical instabilities can appear in both formulations, in particular if very small mesh elements are present inside the absorbing layer, but we explain how these instabilities can be delayed as much as needed by using a stretching factor to reach numerical stability in practice for applications. Fourthly, in the case of adjoint problems with perfectly matched absorbing layers we introduce a computationally efficient boundary storage strategy by saving information along the interface between the CFS-UPML and the main domain only, thus avoiding the need to solve a backward wave propagation problem inside the CFS-UPML, which is known to be highly ill-posed. Finally, by providing several examples we show numerically that our formulation is efficient at absorbing acoustic waves for normal to near-grazing incident body waves as well as surface waves.

Description: 〈span〉〈div〉Abstract〈/div〉We have investigated a locality very well known to mineral collectors, the Yates U-Th prospect near Otter Lake, Québec. There, dikes of orange to pink calcite enclose euhedral prisms of fluorapatite, locally aligned. Early investigators pointed out the importance of micro-inclusions in the prisms. We describe and image the micro-inclusions in two polished sections of fluorapatite prisms, one of them with a millimetric globule of orange calcite similar to that in the matrix. We interpret the globule to have been an inclusion of melt trapped during growth. Micro-globules disseminated in the fluorapatite are interpreted to have crystallized 〈span〉in situ〈/span〉 from aliquots of the boundary-layer melt enriched in constituents rejected by the fluorapatite; the micro-globules contain a complex jigsawed assemblage of carbonate, silicate, and sulfate minerals. Early minerals to crystallize are commonly partly dissolved and partly replaced by lower-temperature phases. Such jigsawed assemblages seem to be absent in the carbonate matrix sampled away from the fluorapatite prisms. The pressure and temperature attained at the Rigolet stage of the Grenville collisional orogeny were conducive to the anatexis of marble in the presence of H〈sub〉2〈/sub〉O. The carbonate melt is considered to have become silicocarbonatitic by assimilation of the enclosing gneisses, which were also close to their melting point. Degassing was important, and the melt froze quickly. The evidence points to a magmatic origin for the carbonate dikes and the associated clinopyroxenite, rather than a skarn-related association.〈/span〉