Rock-magnetic properties of topsoils and urban dust from Morelia (>800,000 inhabitants), Mexico: Implications for anthropogenic pollution monitoring in Mexico’s medium size cities

En el presente trabajo, investigamos la correlación entre algunos parámetros magnéticos y el nivel de contaminación por metales pesados en suelos urbanos de la ciudad de Morelia, en el occidente de México. El estudio magnético fue llevado a cabo en 98 muestras urbanas provenientes de diferentes tipos de uso de suelo. La mayoría de las muestras contienen minerales ferrimagnéticos como responsables de la magnetización, pertenecientes probablemente a las soluciones sólidas de las titanomagnetitas/ titanomaghemitas. Esto es inferido a partir de las mediciones de susceptibilidad en función de la temperatura y de los experimentos de magnetización remanente isotérmica (MRI). Estas mediciones indican además, que la mayoría de las muestras se saturan casi completamente antes de los 300 mT. Adicionalmente, los valores S-200 (S-200 = IRM-200/SIRM, donde IRM-200= magnetización a campo inverso de 200 mT después de la saturación magnética) se encuentran entre 0.7 y 1.0, característicos de minerales de baja coercitividad magnética. Las curvas promedio de magnetización remanente isotérmica de saturación (SIRM) pueden ser usadas como un indicador del nivel de contaminación, ya que estas curvas muestran diferentes valores de saturación de acuerdo al nivel de contaminación por metales pesados: Cu, Ni, Cr y Sr. Estas asociaciones de (titano)magnetitas con metales pesados fueron observadas bajo el Microscopio Electrónico de Barrido, revelando algunos agregados complejos en lugar de las esférulas detectadas comúnmente.In this work, we investigate the correlation between some magnetic parameters and the level of contamination by heavy metals in urban soils from Morelia city, western Mexico. The magnetic study was carried out on 98 urban soils samples belonging to distinct land uses. Most of analyzed samples contain ferrimagnetic minerals as the responsible for magnetization, most probably corresponding to the titanomagnetites/titanomaghemites solid solutions. This is inferred from the susceptibility vs. temperature measurements and the isothermal remanent magnetization (IRM) experiments. These measurements also indicate that most of samples are almost completely saturated before 300 mT. Additionally, the S-200 values (S-200 = IRM-200/ SIRM, where IRM-200= Back-field of 200 mT after magnetic saturation) are between 0.7 and 1.0, characteristic of low coercivity magnetic minerals. The averaged saturation isothermal remanent magnetization (SIRM) curves can be used as an indicator of pollution level, as these curves show different saturation values according to the level of contamination by heavy metals: Cu, Ni, Cr and Sr. These associations of (titano)magnetite with heavy metals were observed by Scanning Electron Microscope revealing some complex aggregates rather than commonly detected spherules.Universidad Nacional Autónoma de México through the projects CONACYT 118971 and PAPIIT IN 22311

Étude microstructurale des opales : application à la déstabilisation par blanchissement

Nous avons démontré que l'unité structurelle de toutes les opales CT est un nano grain de 20 à 40 nm de diamètre. Ces grains peuvent être accumulés sans ordre (opale de feu) ou ordonnés à 1, 2 ou 3 dimensions, pouvant former de l'opale noble par agencement régulier de lépisphères. Nous avons découvert la première opale CT bi disperse où des sphérules de deux diamètres forment un réseau analogue à celui des phases de Laves. La décomposition et attribution des bandes des spectres Raman expérimentaux ont montré pour la première fois que les opales A et CT sont en fait un mélange de domaines de silice amorphe et de cristobalite- en proportion variable. Enfin, nous avons obtenu les premiers résultants expérimentaux permettant de caractériser la déstabilisation par blanchissement. Elle est due à une perte d'eau accompagnée de l'apparition d'eau "cristobalitique", vue en Raman et RMN. Le blanchissement est dû à la diffusion de la lumière par deux phases légèrement différentesWe have demonstrated that the building block of all CT opals is a nanograin, 20 to 40 nm in diameter. These grains can be accumulated at random (fire opal) or may organize with 1, 2 or 3 degrees of order, leading eventually to play-of-colour opal with a regular stacking of lepispheres. We discovered the first bidisperse CT opal, where spheres of two different diameters forma a network analogous to that of Laves phases. The decomposition and attribution of bands in the experimental Raman spectra have demonstrated for the first time that opals A and CT are a mixture in various proportions of amorphous silica and -cristobalite. Finally, we obtained the first experimental results characterizing opal whitening. This destabilization is due in part to a loss of water, together with the formation of " cristobalitic " water, seen in Raman and NMR. Whitening itself is due to light scattering on two slightly different phasesNANTES-BU Sciences (441092104) / SudocSudocFranceF

Estudio mineralógico de la desestabilización de ópalos mexicanos

Este trabajo presenta los resultados del primer estudio mineralógico del fenómeno de desestabilización por blanqueamiento en ópalos mexicanos de origen volcánico. En los espectros Raman de las muestras de ópalo estudiadas se observan bandas características de grupos moleculares de H2O en dos regiones diferentes: alrededor de 3,200 cm-1 para la parte no afectada por la desestabilización (de color naranja) y alrededor de 2,900 cm-1 para la parte desestabilizada (de color blanco). La forma e intensidad de las bandas presentes a 960 cm-1 (grupos Si-OH) y 1,600 cm-1 (grupos moleculares de H2O) constatan esta modificación debida al agua. El análisis térmico diferencial (ATD/ATG) mostró que el contenido total de agua es de 6 a 85% menor en la parte desestabilizada que en la parte naranja inalterada; el agua presente en la parte de color blanco es también más móvil, ya que su eliminación comienza por debajo de los 100 °C. Asimismo, mediante la medición de la superficie específica (método BET) se pudo constatar que, sistemáticamente, la superficie específica es entre 2 y 30 veces más grande para la parte desestabilizada. La microscopia electrónica de barrido (MEB) ha permitido verificar diferencias microestructurales entre las dos partes del ópalo, observándose que en la parte desestabilizada ocurre una descompactación del material. Los resultados obtenidos muestran que la causa de la desestabilización está relacionada con una transformación estructural que involucra la formación de cristobalita de recristalización y la incorporación de grupos H2O moleculares a la estructura de los ópalos volcánicos

Estudio mineralógico de la desestabilización de ópalos mexicanos

Este trabajo presenta los resultados del primer estudio mineralógico del fenómeno de desestabilización por blanqueamiento en ópalos mexicanos de origen volcánico. En los espectros Raman de las muestras de ópalo estudiadas se observan bandas características de grupos moleculares de H2O en dos regiones diferentes: alrededor de 3,200 cm-1 para la parte no afectada por la desestabilización (de color naranja) y alrededor de 2,900 cm-1 para la parte desestabilizada (de color blanco). La forma e intensidad de las bandas presentes a 960 cm-1 (grupos Si-OH) y 1,600 cm-1 (grupos moleculares de H2O) constatan esta modificación debida al agua. El análisis térmico diferencial (ATD/ATG) mostró que el contenido total de agua es de 6 a 85% menor en la parte desestabilizada que en la parte naranja inalterada; el agua presente en la parte de color blanco es también más móvil, ya que su eliminación comienza por debajo de los 100 °C. Asimismo, mediante la medición de la superficie específica (método BET) se pudo constatar que, sistemáticamente, la superficie específica es entre 2 y 30 veces más grande para la parte desestabilizada. La microscopia electrónica de barrido (MEB) ha permitido verificar diferencias microestructurales entre las dos partes del ópalo, observándose que en la parte desestabilizada ocurre una descompactación del material. Los resultados obtenidos muestran que la causa de la desestabilización está relacionada con una transformación estructural que involucra la formación de cristobalita de recristalización y la incorporación de grupos H2O moleculares a la estructura de los ópalos volcánicos

Long-term monitoring of atmospheric pollution in the Maritime Antarctic with the lichen Usnea aurantiaco-atra (Jacq.) Bory: a magnetic and elemental study

International audienceAntarctica is a natural research laboratory thanks to its unique climate, geography, flora and fauna. The conservation of Antarctica's environment is monitored through the Madrid Protocol; however, there are local pollution problems associated with human activities such as research and tourism; in particular, there are negative impacts on air quality from the use of fossil fuels. In this work, we studied for the first time the magnetic and elemental characteristics of the lichen Usnea aurantiaco-atra (Jacq.) Bory collected during different years and from various sites in King George Island, Antarctic Peninsula, as well as some samples of its supporting substrate, for long-term monitoring of atmospheric pollution. Several anthropogenic elements (Ni, Pb, Mo, Cd and Zn) have been identified on sites close to human activities, but also on sites far from them. We found that magnetic proxies from U. aurantiaco-atra samples show a spatial correlation with human influence (scientific bases or airstrips). We observed a correlation between magnetic parameters and Ni and, to a lesser extent, with Cr, Co, V and Ag. The results suggest that by using these magnetic and elemental techniques it is possible to implement monitoring with the lichen U. aurantiaco-atra as a bioindicator for some elements of anthropogenic origi

Archeointensity investigation on pottery vestiges from Puertas de Rolón, Capacha Culture: in search for affinity with other Mesoamerican pre-Hispanic cultures

International audienceWe report the results of a rock magnetic and archeointensity study on pottery fragments recovered at the archaeological site of Puertas de Rolón, Capacha culture (Colima), that is considered one of the most important pre-Classic cultural developments of western Mesoamerica, Mexico. Standard rock magnetic experiments were carried out in order to investigate the reliability of the ancient field strength recovered from studied materials. Six out of the seven analyzed fragments gave reliable intensity determinations. The mean archeointensity value obtained in this study is 35.3 ± 3.4 μT. It is in good agreement with another contemporaneous Mesoamerican mean archeointensity of 34.3 ± 1.1 μT obtained for El Opeño. Statistically similar rock-magnetic parameters between ceramics from El Opeño and Puertas de Rolón potsherds appear to be related to clay-sources with similar geological settings and weathering processes. Alternatively, ancient trade or interexchange between western (Capacha Culture) and eastern Mesoamerica locations, as it has been proposed earlier, seem to be supported by results obtained in this study

Are ceramics and bricks reliable absolute geomagnetic intensity carriers?

International audienceA detailed rock-magnetic and archeointensity study was carried out on materials baked by a western Mexican artisan following traditional techniques to produce faithful reproductions of archeological pieces of the Michoacan region (Western Mesoamerica). The field strength at the site (41.0 +/- 0.51 mu T) was measured with a fluxgate magnetometer and the temperature of the furnace during the baking process was monitored continually by means of a thermocouple placed in the middle of the baking cavity.;Rock-magnetic experiments performed on the raw material (clay and paste) and on in situ prepared baked ceramics and bricks included measurement of thermomagnetic curves (susceptibility and strong-field magnetization versus temperature), first-order reversal curves (FORC), anisotropy of magnetic susceptibility (AMS) and anisotropy of thermoremanent magnetization (A-TRM). Magnetite and probably hematite are present in the samples as carriers of the remanence. Hysteresis ratios suggest that the samples fall in the pseudo-single-domain grain size region, which may indicate a mixture of multidomain and a significant amount of single-domain grains.;Ceramic pieces and brick fragments were subjected to the Thellier-Coe archeointensity method and to an alternative paleointensity experiment, with a TRIAXE magnetometer, in order to check whether they are faithful recorders of the local geomagnetic field strength.;Mean raw-intensity of sample M1 (pottery) overestimates a 7% the expected site intensity, while those corresponding to the brick samples (LQ1 and LQ2) underestimate it 15%. Brick sample LNQ shows a slightly lower intensity (7%), but agrees with the expected site intensity within the experimental uncertainty. The intensity retrieved from the volcanic fragment also included closely reproduces the expected intensity. After A-TRM and cooling-rate corrections, all mean raw values move closer to the expected intensity.;Measurement of temperatures at different parts inside the kiln (bottom and upper parts of both central and peripheral parts) revealed the existence of significant thermal gradients, similar to those observed in ovens from other localities. Different cooling rates are then expected in a single oven.;The scatter in the intensity determinations observed in this study, retrieved from pieces elaborated together in the same oven, could arise from this differentiated cooling rate within the oven and thus, to an inappropriate cooling rate correction in the archeointensity protocol. As this situation was probably reproduced in the baking of ancient ceramic artifacts, a better knowledge of the temperature distribution inside these types of kiln would be desirable in order to choose the appropriate cooling rate correction

The Earth's magnetic field prior to the Cretaceous Normal Superchron: new palaeomagnetic results from the Alto Paraguay Formation

International audienceWe report a detailed palaeomagnetic investigation of 28 lava flows (221 standard palaeomagnetic cores) collected from the Paraguayan part of the Paraná flood basalts (the Alto Paraguay Formation). The initial aims of our study were to (i) document variability of the Earth's magnetic field during the time interval sampled, (ii) obtain a new Early Cretaceous palaeomagnetic pole (PP) for stable South America, and (iii) estimate the extrusion rate of the Paraná magma. We precisely determined the palaeofield direction for 26 sites for which the characteristic remanent magnetizations exhibit small within-site dispersion and high directional stability. No palaeodirections were determined for two sites because of a very complex and erratic behaviour of the remanence during the palaeomagnetic treatments. Nine sites display normal polarity magnetization, whereas nine others are reversely magnetized and the remaining eight sites yield intermediate palaeodirections. The mean palaeomagnetic direction of normal polarity sites give I = −41.8°, D = 4.9°, k = 112, and α95 = 4.9°, whereas reversely magnetized sites give I = 37.1°, D = 181.4°, k = 23, and α95 = 11.1°. The reversal test as defined by McFadden and McElhinny (1990; Classification of the reversal test in paleomagnetism: Geophysical Journal International, v. 103, p. 725–729) is positive, corresponding to Type B with γ = 8.7° and γ0 = 3.7°. This ensures that the palaeomagnetic treatment successfully removed the secondary natural remanent magnetization and that the sampling adequately averaged the palaeosecular variation (PSV). The mean PP position obtained from 18 sites is palaeolongitude (Plong) = 359.2° and palaeolatitude (Plat) = 86.2° S. We show by means of probability plots and formal testing procedures that a Fisher distribution with a concentration parameter K = 65 satisfactorily fits the distribution of virtual geomagnetic poles (VGPs). The PP obtained in this study agrees reasonably well with coeval pole positions, in particular with those obtained from the Central Paraná Magmatic Province in Brazil, Los Adobes, and Misiones in Argentina. However, some other similar age PPs show significant departure that may be attributed to local tectonic rotations or insufficient sampling needed to overcome the PSV. This new PP differs slightly from the reference poles at 135 Ma for South America given by Besse and Courtillot (2002; Apparent and true polar wander and the geometry of the magnetic field in the last 200 million years: Journal of Geophysical Research, v. 107, no. B11, p. 2300). The PSV parameters are in agreement with those obtained from selected data reported for the Cretaceous Normal Superchron (CNS). In contrast, VGP angular dispersion found here is lower with respect to the Jurassic and Plio–Pleistocene data. The intermediate VGPs determined in the present geographical frame show a northern hemisphere cluster of seven VGPs located east of India, whereas one other VGP is located in the vicinity of Australia

Enfoques, estrategias y transdisciplina en los estudios de la sustentabilidad

Este texto contribuye al análisis científico de varias áreas del conocimiento como la filosofía social, la patología, la educación para el cuidado del medio ambiente y la sustentabilidad que inciden en diversas unidades de aprendizaje de la Licenciatura en Educación para la Salud y de la Maestría en Sociología de la SaludEn el presente libro se reflexiona como a pesar de que actualmente tenemos mayor información, conocimientos científicos y nuevas tecnologías, aun no hemos podido solucionar los problemas ambientales, lo que se debe fundamentalmente a que el deterioro ambiental y sus soluciones están relacionadas con diversos factores