Constraints on dolomite formation in a Late Palaeozoic saline alkaline lake deposit, Junggar Basin, north‐west China

Alkaline lakes (pH &gt; 9) are among the few modern sedimentary environments that are hydrochemically favourable for low-temperature dolomite formation. While Mg-clays and Mg-evaporites also form more easily in alkaline environments, few studies have focused on how the kinetically inhibited dolomite wins the competition for Mg2+. Here, a basin-wide survey of the distribution, paragenesis and stable C, O and Mg isotopes of main Mg-rich minerals in the Late Palaeozoic saline alkaline lake deposit of the north-west Junggar Basin, north-west China, is conducted to study the influence of the formation and diagenesis of eitelite, northupite and Mg-clays on dolomite formation. Large, isolated dolomite crystals (20 to 70 μm in diameter), show positive δ13C values (ranging from +1 to +7‰) and a restricted distribution in the mudstones of the lake-transitional zone. These crystals have been interpreted as organogenic dolomite driven by methanogenesis via fermentation of organic substrates. The δ18O values of dolomitic mudstones (from −7.4 to +3.4‰), calcitic mudstones (from −15.1 to −3.3‰) and bedded Na-carbonate evaporites (from +0.08 to +3.7‰), together with their Mg isotopic compositions, suggest that dolomite was not enriched in the most concentrated environments or during stages with most Mg sources, but in the organic-rich deposits containing few other authigenic Mg-rich minerals. Dolomite is at a competitive disadvantage for Mg2+ ions compared to Mg-evaporite and Mg-clay minerals due to its slow crystallization rates and the deficiency of micritic calcium carbonate precursors. However, it can nucleate and progressively grow into large crystals (&gt;20 μm) if bacterial methanogenesis could effectively lower porewater pH (&lt;8.5) and induce the dissolution of generated eitelite, northupite or Mg-clays. These findings suggest that high salinity and/or high alkalinity are not always favourable conditions for dolomite formation and highlight the active role of pH fluctuations in inducing low-temperature dolomite formation.</p

Mg-rich carbonates mediated by a bacterium isolated from an extreme alkaline lake in Central Spain

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSE(MINECO-FEDERpu

Biomineralization of carbonate and phosphate by moderately halophilic bacteria

We investigated the precipitation of carbonate and phosphate minerals by 19 species of moderately halophilic bacteria using media with variable Mg2+/Ca2+ ratios. The precipitated minerals were calcite, magnesium (Mg) calcite, and struvite (MgNH4PO4·6H2O) in variable proportions depending on the Mg2+/Ca2+ ratio of the medium. The Mg content of the Mg-calcite decreased with increasing Ca2+ concentration in the medium. According to the saturation indices, other minerals could also have precipitated. We observed important differences between the morphology of carbonate and phosphate, which may help us to recognize these minerals in natural systems. We studied the growth and pH curves of four bacteria in media specific for carbonate and struvite precipitation. We consider the biomineralization processes that produce carbonate and phosphate minerals, and propose a hypothesis for the lack of struvite in natural environments and ancient rock

Crystal Growth of Inorganic and Biomediated Carbonates and Phosphates

In this chapter, we describe similar crystal growth features in inorganic and biogenic carbonates and phosphates formed in natural environments and in laboratory experiments. We focus on the importance of the kinetics on the crystal habit of carbonates and phosphates precipitated in biological and abiotic systems. We also discuss the influence of the nature and composition of the precipitation medium, as well as the structural control on crystal habit of Ca-Mg carbonates

Effects of salinity, organic acids and alkalinity on the growth of calcite spherulites: Implications for evaporitic lacustrine sedimentation

Lacustrine non‐skeletal carbonates exhibit a diversity of petrographies due to interactions between physico‐chemical and biologically influenced mechanisms. Despite the suggestion that evaporative concentration was involved in the formation of spherulite and shrubby‐bearing carbonate successions in the Pre‐Salt Cretaceous alkaline lakes of the South Atlantic, no consensus exists about the water chemistries promoting these exotic mineral textures. In this work, an experimental approach was developed to evaluate how changes in salinity (NaCl) and biopolymer concentrations (alginic acid) impact calcite growth dynamics from saline and alkaline synthetic solutions. Hydrochemical and petrographical data from selected modern saline/ alkaline environments was compared with experimental datasets to further estimate how the underlying (bio)chemical conditions and lake locations likely converge to allow the formation of calcite spherulite grains in evaporitic settings. Spherulitic calcite from Recent saline lakes and experiments arise from waters with moderate to high [Calcium]/[Alkalinity] ratios ([Ca]/[Alk]) rather than in calcium‐depleted and alkaline‐rich environments which tend to produce single‐crystal calcites during abiotic water mixing or lake evaporation. This is consistent with the assembly of polycrystalline textures being a kinetically controlled feature, forced by remarkably high rates of nucleation. Also, the data analysed do not support a causative relationship between evaporite‐driven salinity fluctuations and the preferential formation of spherulites, shrubs or their intermediate textures. Ubiquitous in saline lakes, organic substances can lower the kinetic thresholds for spherulitic calcite aggregation while microbial photosynthesis can also raise pH, altogether enhancing calcite supersaturation and promoting spherulite formation in waters with moderate‐high [Ca]/[Alk] ratios and high salinities. Localised observations of abiotic spherulites in Recent soda lakes can occur in restricted mixing zones where [Ca]/[Alk] ratios are enhanced. This work highlights the roles of concentration regimes associated with biopolymers and microbial metabolism against the background salinity fluctuations in determining the morphological and textural transitions in lacustrine carbonate minerals

Microbial mediated formation of Fe-carbonate minerals under extreme acidic conditions

Discovery of Fe-carbonate precipitation in Rio Tinto, a shallow river with very acidic waters, situated in Huelva, South-western Spain, adds a new dimension to our understanding of carbonate formation. Sediment samples from this low-pH system indicate that carbonates are formed in physico-chemical conditions ranging from acid to neutral pH. Evidence for microbial mediation is observed in secondary electron images (Fig. 1), which reveal rod-shaped bacteria embedded in the surface of siderite nanocrystals. The formation of carbonates in Rio Tinto is related to the microbial reduction of ferric iron coupled to the oxidation of organic compounds. Herein, we demonstrate for the first time, that Acidiphilium sp. PM, an iron-reducing bacterium isolated from Rio Tinto, mediates the precipitation of siderite (FeCO3) under acidic conditions and at a low temperature (306C). We describe nucleation of siderite on nanoglobules in intimate association with the bacteria cell surface. This study has major implications for understanding carbonate formation on the ancient Earth or extraterrestrial planetsThis work was supported by the European research project ERC-250350/IPBSL. A.S.-N. acknowledges support from the P11-RNM-7067 (Junta de Andalucía-C.E.I.C.-S.G.U.I.T.) projec

Microbial mediated formation of Fe-carbonate minerals under extreme acidic conditions

Discovery of Fe-carbonate precipitation in Rio Tinto, a shallow river with very acidic waters, situated in Huelva, South-western Spain, adds a new dimension to our understanding of carbonate formation. Sediment samples from this low-pH system indicate that carbonates are formed in physico-chemical conditions ranging from acid to neutral pH. Evidence for microbial mediation is observed in secondary electron images (Fig. 1), which reveal rod-shaped bacteria embedded in the surface of siderite nanocrystals. The formation of carbonates in Rio Tinto is related to the microbial reduction of ferric iron coupled to the oxidation of organic compounds. Herein, we demonstrate for the first time, that Acidiphilium sp. PM, an iron-reducing bacterium isolated from Rio Tinto, mediates the precipitation of siderite (FeCO3) under acidic conditions and at a low temperature (30°C). We describe nucleation of siderite on nanoglobules in intimate association with the bacteria cell surface. This study has major implications for understanding carbonate formation on the ancient Earth or extraterrestrial planets.European research project ERC-250350/IPBSL. A.S.-N.acknowledges support from the P11-RNM-7067 (Junta de Andaluc a-C.E.I.C.-S.G.U.I.T.) projectPeer Reviewe

La complejización del objeto de estudio urbano, un aporte al proceso de enseñanza en la Cátedra Urbanismo II, FAUD, UNC

Ponencia presentada en el XXXII Encuentro y XVII Congreso ARQUISUR. Habitar la Ciudad, Tiempo y Espacio. Córdoba, 2013Esta ponencia tiene la finalidad de reflexionar sobre la complejidad del objeto de estudio urbano y su incidencia en las prácticas metodológicas de la enseñanza de procesos de planificación urbano - territorial. Para ello, se expone la experiencia de las prácticas pedagógicas que se vienen desarrollando en la Cátedra Urbanismo II, FAUD, UNC, en los últimos tres años (2011, 2012 y 2013 en curso). El desarrollo del Trabajo Práctico tiene como objetivo abordar el Ordenamiento Urbano, Territorial y Ambiental de una localidad de entre 10.000 y 100.000 habitantes, inserta en el Área Metropolitana Córdoba. Esta Área no constituye un ámbito jurídico, sino que es un hecho funcional conformado por un sistema de centros urbanos entre los que se genera una intensa dinámica diaria, alta movilidad de personas, importantes flujos de bienes, servicios y capital, grandes variaciones en los valores del suelo y alta presión sobre el mismo, situaciones que van variando según las restricciones y posibilidades locales. El abordaje de la práctica simulada de ordenamiento urbano se realiza en un proceso de Planificación y Gestión Urbanas con enfoque Estratégico, desde una mirada integral, pluriescalar y sistémica. En la programación del trienio 2011-2013, se trabajó en el año 2011 con el Municipio de Pilar y en el 2012 con el de Río Segundo, en forma independiente. En el año 2013 nos planteamos el reto de introducir nuevas miradas disciplinares del Urbanismo y pasar de entender la visión estratégica de competencia entre ciudades a otra de centros articulados y de competencia entre regiones. La proximidad geográfica de ambos municipios, solo separados por el Rio Segundo, nos permite pensar en una unidad conurbada como área de oportunidad, potenciando la identidad local de cada municipio. Esta experiencia, al mismo tiempo, permite indagar e introducir nuevas figuras de gestión y ensayar proyectos mancomunados. Este nuevo abordaje del trabajo práctico tiene la ventaja de poder aplicar similares criterios de análisis para las dos localidades. De esta manera se aprovecha la experiencia de los trabajos 2011-2012. La dinámica de elaboración del diagnóstico comparativo entre ambos centros aporta reflexión y síntesis al proceso de aprendizaje del alumno y abre una mirada propositiva desde la complementariedad de los recursos y posibilidades locales. Por otra parte, el trabajo simultáneo con dos municipios permite ensayar escenarios de actuación conjunta, con los beneficios y problemáticas que involucra una gestión articulada, contemplando la diversidad de situaciones, actores y gestores de los procesos urbano-territoriales, situación que posibilita encarar proyectos estratégicos compartidos, que de otra manera serían difíciles o imposibles de afrontar.Fil: Donicelli, Mario. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Caracciolo, Román. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Debat, Mariana. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Cebrián, Victoria. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Sánchez, Mónica. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Pulido, María Elisa. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Torres, César. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaFil: Ruiz, Jorge Mario. Universidad Nacional de Córdoba. Facultad de Arquitectura, Urbanismo y Diseño; ArgentinaOtras Ingenierías y Tecnología

MTOC translocation modulates IS formation and controls sustained T cell signaling

The translocation of the microtubule-organizing center (MTOC) toward the nascent immune synapse (IS) is an early step in lymphocyte activation initiated by T cell receptor (TCR) signaling. The molecular mechanisms that control the physical movement of the lymphocyte MTOC remain largely unknown. We have studied the role of the dynein–dynactin complex, a microtubule-based molecular motor, in the process of T cell activation during T cell antigen–presenting cell cognate immune interactions. Impairment of dynein–dynactin complex activity, either by overexpressing the p50-dynamitin component of dynactin to disrupt the complex or by knocking down dynein heavy chain expression to prevent its formation, inhibited MTOC translocation after TCR antigen priming. This resulted in a strong reduction in the phosphorylation of molecules such as ζ chain–associated protein kinase 70 (ZAP70), linker of activated T cells (LAT), and Vav1; prevented the supply of molecules to the IS from intracellular pools, resulting in a disorganized and dysfunctional IS architecture; and impaired interleukin-2 production. Together, these data reveal MTOC translocation as an important mechanism underlying IS formation and sustained T cell signaling