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Summary A model of radial drifting and oscillating dipoles to represent geomagnetic palaeosecular variations, which showed to be appropriate for the Southern Hemisphere, is evaluated for the Northern Hemisphere. After a new fitting of some involved parameters, its theoretical results are compared with the palaeomagnetic data of Lake de Bouchet (France) and the Black Sea. A time lag between the declination and inclination profiles is observed in both cases. A good cross-correlation coefficient is obtained for the declination and inclination data.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990. 相似文献
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Romina V. Achaga Maria A. Irurzun Claudia S. G. Gogorza Avto Goguitchaichvili Juan Morales Daniel Loponte Ana M. Sinito 《Studia Geophysica et Geodaetica》2017,61(2):318-335
Laguna Melincué is a shallow lake located in Santa Fe Province, Argentina (33°41′27.8″S, 61°31′36.5″W). The catchment area is around 1495 km2 and it is located in the Pampean Plains. It was reduced to 678 km2 by the construction of the San Urbano channel in 1941 and reconditioned in 1977, which was built to avoid floods. The floods are related to some El Niño episodes, with high precipitation events. The lake has been previously studied from different approaches, mainly to understand hydrological and climatic variations, but more multidisciplinary studies are needed to understand its complex hydrological situation. Here we present the first paleomagnetic and rock magnetic studies made on a short sediment core collected from the lake in order to contribute to identifying paleoclimatic proxies and to present the first paleomagnetic results for the site. Rock magnetic analyses suggest that the well-preserved magnetic mineralogy is dominated by pseudo single-domain (titano)magnetite and/or maghemite. The results also indicate that a stable characteristic remanent magnetisation can be isolated and thus the directions of the geomagnetic field may be obtained, providing evidence for the use of this lake for paleomagnetic and paleoenvironmental studies. Changes in magnetic grain size and concentration of magnetic minerals suggest environmental variations and changes in the lake level, which are consistent with historical reports. The paleomagnetic results agree well with Cals3k.3 model for inclination and declination of the geomagnetic field except for the dry period probably due to the fact that the core was extracted near the shore. 相似文献
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Mauro A. E. Chaparro Marcos A. E. Chaparro Ana M. Sinito 《Environmental Earth Sciences》2012,66(5):1477-1485
In this contribution, a methodology is reported in order to build an interval fuzzy model for the pollution index PLI (a composite index using relevant heavy metal concentration) with magnetic parameters as input variables. In general, modelling based on fuzzy set theory is designed to mimic how the human brain tends to classify imprecise information or data. The “interval fuzzy model” reported here, based on fuzzy logic and arithmetic of fuzzy numbers, calculates an “estimation interval” and seems to be an adequate mathematical tool for this nonlinear problem. For this model, fuzzy c-means clustering is used to partition data, hence the membership functions and rules are built. In addition, interval arithmetic is used to obtain the fuzzy intervals. The studied sets are different examples of pollution by different anthropogenic sources, in two different study areas: (a) soil samples collected in Antarctica and (b) road-deposited sediments collected in Argentina. The datasets comprise magnetic and chemical variables, and for both cases, relevant variables were selected: magnetic concentration-dependent variables, magnetic features-dependent variables and one chemical variable. The model output gives an estimation interval; its width depends on the data density, for the measured values. The results show not only satisfactory agreement between the estimation interval and data, but also provide valued information from the rules analysis that allows understanding the magnetic behaviour of the studied variables under different conditions. 相似文献
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Marcos A. E. Chaparro Juan M. Lirio Héctor Nuñez Claudia S. G. Gogorza Ana M. Sinito 《Environmental Geology》2005,49(1):30-43
Magnetic properties of lagoon and stream sediments from Chascomús area (Buenos Aires Province) and the relevance of various magnetic parameters as giving pollution status are studied in the present work. This work is focussed on magnetic parameters, such as concentration-dependent (magnetic susceptibility, saturation anhysteric and isothermal remanent magnetisation) and feature-dependent parameters (S-ratio, coercivity of remanence, anhysteric susceptibility/magnetic susceptibility-ratio), as pollution indicators. Firstly and most importantly, different magnetic parameters and chemical measurements were correlated in order to investigate their goodness, obtaining the best results for feature-dependent magnetic parameters. Coercivity of remanence correlate very well with chemical variables, showing correlations at high level of significance up to 0.9094, and the anhysteric susceptibility/magnetic susceptibility-ratio also shows very good correlations (up to 0.8376). Some results and advantages of using a new experimental method in order to discriminate hard and soft magnetic phases are also shown. This method uses alternately backfield isothermal remanent magnetisation and alternating field demagnetisation. From the experimental separation, the presence of hard magnetic phases in some samples was confirmed. 相似文献
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M.?A.?E.?ChaparroEmail author J.?C.?Bidegain A.?M.?Sinito S.?S.?Jurado C.?S.?G.?Gogorza 《Environmental Geology》2004,45(5):654-664
Anthropogenic influence, mainly due to urban and industrial activities, may affect fluvial environments and soils, via atmospheric contamination and liquid and solid waste.Continuing previous works on stream sediments and soils, the Gran La Plata area was chosen. In this area, located in the Northeast of Buenos Aires Province (Argentina), several streams and soils were sampled. The streams have similar characteristics, although some of them have a higher input of pollutants (fluvial effluents, fly ashes, solid wastes, etc.). The studied soils have different pedological development.Magnetic and chemical studies were carried out in the laboratory. Analyses of the results indicated that the behavior of magnetic parameters can be related to the variations of heavy metal contents in stream sediments but there is not a good correlation in soils. The comparison between both environments (stream-sediment and soils) reveals a different impact of pollutants. Magnetite, especially PSD grains, seems to be the main carrier for both environments. 相似文献
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Marcos A. E. Chaparro Mauro A. E. Chaparro P. Rajkumar V. Ramasamy Ana M. Sinito 《Environmental Earth Sciences》2011,63(2):297-310
This contribution constitutes a new study using magnetic parameters and trace element determinations of pollutants in river
sediments from the Tamil Nadu state. The Vellar River covers a total length of about 200 km and flows into the Bay of Bengal.
Sediment samples were collected at different sediment depths (up to 90 cm) from 12 sites to investigate their magnetic properties
(27 samples) and the contents of trace elements (21 out of 27 samples) along the river; as well as to perform magnetic studies
for various grain size fractions (16 sub samples). The magnetic results of magnetic susceptibility and remanent magnetizations
suggest that the magnetic signal of these sediments is controlled by ferrimagnetic minerals magnetite-like minerals and a
minor contribution of antiferromagnetic carriers (such as hematite minerals). Detailed studies of selected samples showed
a higher magnetic concentration in finer grain-sized fractions and a slightly different magnetic mineralogy. Magnetic concentration-dependent
parameters evidenced high values, which, together with the background values, allowed us to identify magnetic enhancement
at some sites. The Pearson correlation and multivariate statistical studies (Principal Component Analysis, Canonical Correlation
Analysis) supported the relationship between the magnetic and chemical variables; in particular, magnetic susceptibility,
anhysteretic and isothermal remanent magnetization are closely correlated to Co, Cr, Cu, Fe, V, Zn, and the pollution load
index. In addition, Principal Coordinate Analysis and fuzzy C-means cluster analysis allowed us to make a classification and
to perform a magnetic-chemical characterization of the data into four groups, thereby identifying critical (possibly polluted)
sites from the Vellar River. 相似文献