Crystal and molecular structure and spectroscopic behavior of isotypic synthetic analogs of the oxalate minerals stepanovite and zhemchuzhnikovite     

Oscar E. Piro  Gustavo A. Echeverría  Ana C. González-Baró  Enrique J. Baran 《Physics and Chemistry of Minerals》2016,43(4):287-300

The crystal structure of synthetic stepanovite, Na[Mg(H₂O)₆][Fe(C₂O₄)₃]·3H₂O, and zhemchuzhnikovite, Na[Mg(H₂O)₆][Al_0.55Fe_0.45(C₂O₄)₃]·3H₂O, has been determined by single-crystal X-ray diffraction methods. The compounds are isotypic to each other and to the previously reported Na[Mg(H₂O)₆][M(C₂O₄)₃]·3H₂O (M: Cr, Al). They crystallize in the trigonal P3c1 space group with Z = 6 molecules per unit cell and (hexagonal axes) a = 17.0483(4), c = 12.4218(4) Å for the iron compound, and a = 16.8852(5), c = 12.5368(5) Å for the Al/Fe solid solution. Comparison of our crystallographic results with previous X-ray diffraction and chemical data of type stepanovite and zhemchuzhnikovite minerals provides compelling evidence that these natural materials possess the same crystal and molecular structure as their synthetic counterparts. It is shown that the originally reported unit cell for stepanovite represents a pronounced sub-cell and that the correct unit cell and space group are based on weak superstructure reflections. The infrared and Raman spectra of both synthetic analogs were also recorded and are briefly discussed.  相似文献   

Estimation of monthly global solar irradiation using the Hargreaves–Samani model and an artificial neural network for the state of Alagoas in northeastern Brazil     

Gustavo Bastos Lyra  Sidney Sára Zanetti  Anderson Amorim Rocha Santos  José Leonaldo de Souza  Guilherme Bastos Lyra  José Francisco Oliveira-Júnior  Marco Antônio Maringolo Lemes 《Theoretical and Applied Climatology》2016,125(3-4):743-756

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Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past,addressing an uncertain future          下载免费PDF全文

Mauricio Flores  Jorge Núñez  Jorge Oyarzún  Gustavo Freixas  Hugo Maturana  Ricardo Oyarzún 《水文研究》2017,31(3):498-513

This study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters (pH, SO₄, Fe, Cu, and As) in the upper area of the Elqui River basin in North‐Central Chile. A correlation analysis determined statistically significant positive relationship for SO₄‐Cu, Fe‐As, and Fe‐Cu. In terms of historical behaviour, no statistically significant trends were detected for precipitation or temperature. In contrast, for flow, there is an overall decreasing pattern for the entire area of study, although only in one case this trend was statistically significant. Along with the aforementioned analysis, a characterization of the flow‐water quality relationships is considered for the time period analyzed. Although erratic behaviours were confirmed, a negative (i.e., inverse) flow‐concentration relationship was identified for SO₄, a positive (i.e., direct) relationship for Fe, and undefined relationships for As and Cu were obtained. From these analyses and based on previous studies on projections regarding climate change for the Andean region, and in particular for the upper Elqui zone, an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed. It is likely that a decrease in surface flow, as a consequence of climate change could translate into improvements in water quality in terms of Fe and eventually As and Cu, but into an impairment in the case of SO₄. In any case, this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the Claro River, which currently play an important role in depurating or diluting contaminants in the waters of the Elqui River. Finally, it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations, which are considered to be highly vulnerable to climate change and variability.  相似文献   

Conodont geothermometry of the lower Paleozoic from the Precordillera (Cuyania terrane), northwestern Argentina     

Gustavo G. Voldman  Guillermo L. Albanesi  Víctor A. Ramos 《Journal of South American Earth Sciences》2010,29(2):278-288

The thermal history of the Precordillera terrane of northwestern Argentina has been constrained by the conodont colour alteration index (CAI) in combination with previously published paleothermal data (e.g., illite crystallinity and clay mineral assemblages). The pattern of paleotemperatures displays an increase in paleotemperatures to the west and south of the basin. This configuration shows a gradual and continuous transition from diagenesis to low-grade metamorphism, which is apparently not controlled by any of the morpho-structural subdivisions of the Precordillera (i.e., Western, Central, or Eastern). According to our results, the lower Paleozoic sedimentary burial played a secondary role in the heating of the Precordillera. Instead, the predominant component was loading by thrust sheets, which reflects the effects of the Devonian collision of Chilenia, particularly, in the Western Precordillera. Conversely, our paleothermometric data from the easternmost exposures of the Precordillera do not evidence anomalies referable to any of the accretionary events that contributed to the early Paleozoic building of the southern proto-Andean margin of Gondwana. Instead, the expected thermally altered conodonts from the Cuyania accretion are represented by metamorphosed conodont elements transported to the deeper settings of the west. The CAI data also suggest that overburden depth varied from ca. 3.6 km in the shelf region of the Eastern Precordillera to ca. 12 km in the slope to rise deposits of the Western Precordillera, thus providing constrains for the palinspastic restoration across the orogen. On the other hand, the smooth increase of peak paleotemperatures to the south of the Precordillera is associated with the exposure of deeper crustal levels at that sector, probably related to larger shortening due to stronger collisional effects, or alternatively, a weaker mechanical response of its elastic lithosphere.  相似文献   

Analysis of an illustrative interaction between structural features and earthworm populations in Brazilian ferralsols     

Michel Brossard  Gustavo Adolfo de Freitas Fregonezi  Maria de Fátima Guimarães  Cristiane de Conti Medina  Amarildo Pasini  Lourival Vilela  Miguel Angel Ayarza 《Comptes Rendus Geoscience》2012,344(1):41-49

Ferralsols are characterized by poorly-defined horizons, weak macrostructure and strong development of a fine granular structure comprising subangular micro-aggregates. In this study, the morphological and physical modifications caused by earthworm activity in a clayey ferralsol were analysed. After describing soil structures, undisturbed samples were taken for evaluating aggregates and determining clod bulk density and particle density. Soil water retention properties were measured and an inventory of soil invertebrate macrofauna was created. The structural and porous transformations were due to aggregates created by earthworm activity. Changes in bulk density can be associated with pore modifications caused by a change in the proportions of aggregate types, and a notable reduction of total porosity was measured, tending to increase soil volume with dense aggregates. Structural modifications affected the topsoil down to 0.5 m and water retention between −1 and −33 kPa, the principal water compartment of these soils.  相似文献   

Geochronology and Landscape Development Along the Middle Río Quequén Grande at the Paso Otero Locality,Pampa Interserrana,Argentina     

Eileen Johnson  Vance T. Holliday  Gustavo Martínez  María Gutirrez  Gustavo Politis 《Geoarchaeology》2012,27(4):300-323

The Paso Otero Locality is a cluster of archaeological sites within the middle Río Quequén Grande basin located in the northern coastal plain of Argentina. The valley fill is Holocene alluvial, eolian, and palustrine sediment, including the top of the Guerrero Member (∼10,000 ¹⁴C yr B.P.), upper Río Salado Member (∼3000 ¹⁴C yr B.P.), and lower La Postrera Formation (∼2400 ¹⁴C yr B.P.). Regional soils include the Puesto Callejón Viejo (10,000 to 9400 ¹⁴C yr B.P.) and the Puesto Berrondo (∼4800 ¹⁴C yr B.P.). Radiocarbon sampling of buried A‐horizons on both sides of the river produced 17 dates considered reliable. The geoarchaeological information allows exploration of the implications for the formation of the archaeological record. Similar geological processes of differential intensity have resulted in contexts of different archaeological resolution and integrity. The Paso Otero Locality provides both a local and regional view of late Quaternary events and processes for the middle basin of the Río Quequén Grande.  相似文献   

Simulation of Geological Contacts from Interpreted Geological Model Using Multiple-Point Statistics   总被引：2，自引：1，他引：1  

Alexandre Boucher  Joao Felipe Costa  Luis Gustavo Rasera  Eduardo Motta 《Mathematical Geosciences》2014,46(5):561-572

Applications of multiple-point statistics (mps) algorithms to large non-repetitive geological objects such as those found in mining deposits are difficult because most mps algorithms rely on pattern repetition for simulation. In many cases, an interpreted geological model built from a computer-aided design system is readily available but suffers as a training image due to the lack of patterns repetitiveness. Porphyry copper deposits and iron ore formations are good examples of such mining deposits with non-repetitive patterns. This paper presents an algorithm called contactsim that focuses on reproducing the patterns of the contacts between geological types. The algorithm learns the shapes of the lithotype contacts as interpreted by the geologist, and simulates their patterns at a later stage. Defining a zone of uncertainty around the lithological contact is a critical step in contactsim, because it defines both the zones where the simulation is performed and where the algorithm should focus to learn the transitional patterns between lithotypes. A larger zone of uncertainty results in greater variation between realizations. The definition of the uncertainty zone must take into consideration the geological understanding of the deposit, and the reliability of the contact zones. The contactsim algorithm is demonstrated on an iron ore formation.  相似文献   

Acoustic characterization of gelatinous plankton aggregations: four case studies from the Argentine continental shelf   总被引：3，自引：2，他引：3  

Colombo  Gustavo Alvarez; Mianzan  Hermes; Madirolas  Adrian 《ICES Journal of Marine Science》2003,60(3):650-657

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Imprints of mass accretion on properties of galaxy clusters     

Andreas Faltenbacher  Brandon Allgood  Stefan Gottlöber  Gustavo Yepes  Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2005,362(3):1099-1108

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Clues to the nature of damped Lyman α systems from chemical evolution models     

Gustavo A. Lanfranchi  Amancio C. S. Friaça 《Monthly notices of the Royal Astronomical Society》2003,343(2):481-504

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