Evidencias geoquímicas y neomorfismo en rocas de la Formación Chachao (Valanginiano)-anticlinal Malargüe, Mendoza

Geochemical features and neomorphism of Chachao Formation calcareous rocks (Valanginian)-Malargüe Anticline, Mendoza. The Lower Cretaceous Chachao Formation in the Malargüe anticline area consists of wackestone, packstone, grainstone and minor mudstone rich in benthic fauna (mainly bivalves) which were deposited in a shallow carbonate ramp as previous sedimentological studies have proposed. Standard petrographic, XRD, SEM, cathodoluminiscense and trace element determinations composition of micrite and microsparite mosaic crystals were undetaken in order to characterize their original mineralogy. The SEM shows that the mud fraction is composed of a mosaic texture of subhedral to anhedral micrite and microsparite crystals, both showing similar features such as smooth (unpitted) surfaces and lack of aragonite relicts. Crystal morphology also rules out the possible presence of aragonite. These features together with the microfabric, low Sr content (average: 592 ppm) of both micrite and microsparite point to an original high-magnesium calcite composition of the muds. Geochemical data from the micrite and microsparite of the mud-supported rocks of the Chachao Formation show two contrasting trends : decreasing-upward Sr and Na concentrations and increasing-upward Mg and Mn concentrations. The loss of Sr and Na are related to mineralogical stabilization of metastable carbonate particles involving the inversion of high-magnesium calcite to low-magnesium calcite, whereas local dolomitization in the upper part of the studied sequence has formed dolomite crystals showing different stages of dissolution due to meteoric and marine water influences. © 1999 Asociación Geológica Argentina.Fil:Palma, R.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Lanés, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Miretzky, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Marine Phosphates in the Paleogene oflsla Grande de Tîerra del Fuego

Phosphate prospecting in marine sedimentary rocks of the Marginal and Austral basins of the Isla Grande de Tierra del Fuego resulted in the first discovery of phosphatic beds in the Paleogene Rio Claro Formation. Phosphatic anomalies of up to 20.1% P2U5 in concretions and up to 2% PaOs in bulk rock offer promising opportunities for systematic prospection on the Isla Grande de Tierra del Fuego. The phosphatic beds are conglomerates, coquinas and conglomeratic sandstones interbedded with thick mudstone packets. They belong to the condensed-type phosphatic beds, which are the product of erosion and reworking of concretions developed in fine sediments. Phosphate concretions containing glauconite, together with abundant glauconite in the same and closely associated beds, indicate a common syn-sedimentary to earlydiagenetic origin for both minerals, via recycling of sedimentary iron. This process occurred on a shelf with low sedimentation rates, pointing to high sea-level stands and marked interruptions in the sedimentation of the thick Paleogene sedimentary sequence of the Austral Basin . The deposit point to the existence and extension of this early Cenozoic phosphogenic episode to high latitudes in the Southern Hemisphere. © 1998 Asociacidn Geoldgica Argentina.Fil:Olivero, E.B. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Scasso, R.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Miretzky, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

La teoría de Florentino Ameghino y el Plan Maestro Integral Cuenca del Río Salado en el tramo de la desembocadura en la Bahía de Samborombón : Propuesta de construcción de un dique de retención

The Theory of Florentino Ameghino and the Plan Maestro Integral Cuenca del Río Salado at the mouth in the Samborombón Bay. A retention dam building proposal. Florentino Ameghino established that the Buenos Aires Province needs retention structures and not drainage ones in order to prevent drought and flood events. In the lower Salado River drainage basin, Channel Aliviador and Channel 15, that reach the Samborombón Bay, were built with the purpose of control water excess during flooded periods. But Channel 15 was made wider and deeper during 1997, then almost all the water coming from the river goes directly to the Samborombón Bay and this causes a lesser supply of freshwater, that promotes a change in the ecological and socioeconomic conditions in that region. As a consequence, the government taking into account the results of the project Plan Maestro Integral Cuenca del Río Salado (PMI), decided to build threshold bottom dams in the two channels. On the other way, near the mouth of Samborombón Bay, it is located the rock shell littoral chain, which generates an aquifer of a low salinity water. At present, hydrochemical studies indicate that the absence of the river makes the water of the aquifer goes to the bed of the river, which reaches the bay in the moment of low tide and, on the contrary, during high tide a mix with high salinity water coming from the bay takes place. In both cases a loss of freshwater occurs. So in order to minimize this effect, the construction of a retention dam was suggested in a previous work. Since, once the dams of the PMI will be concluded, still a probability of a lack of water may persist in case of drought event as well as for the intensive use of water in the rest of the drainage basin, then the aim of the present work is to maintain the proposal of the construction of the retention dam to assure a source of freshwater in the region and to preserve the rock shell littoral chain aquifer.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

La teoría de Florentino Ameghino y el Plan Maestro Integral Cuenca del Río Salado en el tramo de la desembocadura en la Bahía de Samborombón : Propuesta de construcción de un dique de retención

The Theory of Florentino Ameghino and the Plan Maestro Integral Cuenca del Río Salado at the mouth in the Samborombón Bay. A retention dam building proposal. Florentino Ameghino established that the Buenos Aires Province needs retention structures and not drainage ones in order to prevent drought and flood events. In the lower Salado River drainage basin, Channel Aliviador and Channel 15, that reach the Samborombón Bay, were built with the purpose of control water excess during flooded periods. But Channel 15 was made wider and deeper during 1997, then almost all the water coming from the river goes directly to the Samborombón Bay and this causes a lesser supply of freshwater, that promotes a change in the ecological and socioeconomic conditions in that region. As a consequence, the government taking into account the results of the project Plan Maestro Integral Cuenca del Río Salado (PMI), decided to build threshold bottom dams in the two channels. On the other way, near the mouth of Samborombón Bay, it is located the rock shell littoral chain, which generates an aquifer of a low salinity water. At present, hydrochemical studies indicate that the absence of the river makes the water of the aquifer goes to the bed of the river, which reaches the bay in the moment of low tide and, on the contrary, during high tide a mix with high salinity water coming from the bay takes place. In both cases a loss of freshwater occurs. So in order to minimize this effect, the construction of a retention dam was suggested in a previous work. Since, once the dams of the PMI will be concluded, still a probability of a lack of water may persist in case of drought event as well as for the intensive use of water in the rest of the drainage basin, then the aim of the present work is to maintain the proposal of the construction of the retention dam to assure a source of freshwater in the region and to preserve the rock shell littoral chain aquifer.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

La teoría de Florentino Ameghino y el Plan Maestro Integral Cuenca del Río Salado en el tramo de la desembocadura en la Bahía de Samborombón : Propuesta de construcción de un dique de retención

The Theory of Florentino Ameghino and the Plan Maestro Integral Cuenca del Río Salado at the mouth in the Samborombón Bay. A retention dam building proposal. Florentino Ameghino established that the Buenos Aires Province needs retention structures and not drainage ones in order to prevent drought and flood events. In the lower Salado River drainage basin, Channel Aliviador and Channel 15, that reach the Samborombón Bay, were built with the purpose of control water excess during flooded periods. But Channel 15 was made wider and deeper during 1997, then almost all the water coming from the river goes directly to the Samborombón Bay and this causes a lesser supply of freshwater, that promotes a change in the ecological and socioeconomic conditions in that region. As a consequence, the government taking into account the results of the project Plan Maestro Integral Cuenca del Río Salado (PMI), decided to build threshold bottom dams in the two channels. On the other way, near the mouth of Samborombón Bay, it is located the rock shell littoral chain, which generates an aquifer of a low salinity water. At present, hydrochemical studies indicate that the absence of the river makes the water of the aquifer goes to the bed of the river, which reaches the bay in the moment of low tide and, on the contrary, during high tide a mix with high salinity water coming from the bay takes place. In both cases a loss of freshwater occurs. So in order to minimize this effect, the construction of a retention dam was suggested in a previous work. Since, once the dams of the PMI will be concluded, still a probability of a lack of water may persist in case of drought event as well as for the intensive use of water in the rest of the drainage basin, then the aim of the present work is to maintain the proposal of the construction of the retention dam to assure a source of freshwater in the region and to preserve the rock shell littoral chain aquifer.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

Chromium(III) biosorption onto spent grains residual from brewing industry : equilibrium, kinetics and column studies

The use of industrial wastes for wastewater treatment as a strategy to their re-use and valorisation may provide important advances toward sustainability. The present work gives new insights into heavy metal biosorption onto low-cost biosorbents, studying chromium(III) biosorption onto spent grains residual from a Portuguese brewing industry both in batch and expanded bed column systems. Experimental studies involved unmodified spent grains and spent grains treated with NaOH. Metal uptake followed a rapid initial step, well described by the pseudo-second-order kinetic model up to 27 h, indicating chemisorption to be the rate-limiting step. Beyond this period intraparticle diffusion assumed an important role in the uptake global kinetics. The best fit for equilibrium data was obtained using the Langmuir model, with unmodified spent grains having the higher maximum uptake capacity (q max = 16.7 mg g1). In open system studies, using expanded bed columns, the best performance was also achieved with unmodified spent grains: Breakthrough time (C/C i = 0.25) and total saturation time (C/C i = 0.99) occurred after 58 and 199 h of operation, corresponding to the accumulation of 390 mg of chromium(III), 43.3 % of the total amount entering the column. These results suggest that alkali treatment does not improve spent grains uptake performance. Changes in biomass composition determined by Fourier transform infrared spectroscopy suggested hydroxyl groups and proteins to have an important role in chromium(III) biosorption. This study points out that unmodified spent grains can be successfully used as low-cost biosorbent for trivalent chromium.The authors would like to thank the Portuguese brewing industry UNICER for all the support and FCT (Fundacao para a Ciencia e a Tecnologia) financial support through the Grant PRAXIS XXI/BD/15945/98