María A. Irurzun

Review of magnetism and heavy metal pollution studies of various environments in Argentina

In recent years, the number of studies of pollution and magnetic proxies for environmental pollution in developed countries, especially European and North American countries, has gradually increased from the 80’s to date. Despite this trend that shows a positive interest in taking care of the environment and researching into the environmental impact of several human activities, pollution studies in Latin American countries have been reducing in number. Moreover, studies of magnetic proxies for pollution are scarce; in particular, studies of this nature has been carried out in Argentina over the past few years by Chaparro and coworkers. Studies of magnetic enhancement in soils due to the burning mechanism are discussed and the results of burnt soils affected by fires of different nature and natural soils are compared, taking into account their magnetic carriers. Nevertheless, this article deals mainly with the first studies of magnetic proxies for pollution conducted in a province in Argentina. Soils, lagoon and stream sediments from three areas were studied. These areas comprise La Plata, Chascomús, and Tandil districts. The influence of pollution was investigated in Tandil and La Plata, revealing magnetic enhancement and the presence of pollutants only in Tandil soils. On the other hand, stream and lagoon sediments were studied in La Plata and Chascomús. Magnetic carriers and the contents of some heavy metals were identified and investigated in both areas separately. Magnetic parameters show distinctive points and wide areas affected by pollution. Furthermore, this magnetic inference is supported by high contents of heavy metals, especially lead and zinc. Finally, a new statistical study of multiple correlation analysis concerning data from La Plata and Chascomús areas was tried in order to investigate the existence of a linear relation between sets of several magnetic parameters and several chemical variables.

Relative paleointensity of the geomagnetic field over the last 21,000 years BP from sediment cores, Lake El Trébol (Patagonia, Argentina)

Four cores from Lake El Trébol (Patagonia, Argentina) have been used to estimate regional geomagnetic paleointensity. The rock magnetic studies indicate that the magnetic mineralogy of the clay-rich sediments is dominated by pseudo-single domain magnetite in a range of grain sizes and concentration which are suitable for paleointensity studies. The remanent magnetisation at 20 mT (NRM20 mT) has been normalised using the an-hysteric remanent magnetisation at 20 mT (ARM20 mT), the saturation of the isothermal remanent magnetisation at 20 mT (SIRM20 mT) and the low field magnetic susceptibility (k). Coherence function analysis indicates that the normalised records are free of environmental influences. Our paleointensity (NRM20 mT/ARM20 mT) versus age curve shows good agreement with published record from another lake in Argentina and with records from other parts of the world, suggesting that, in suitable sediments, paleointensity of the geomagnetic field can give a globally coherent, dominantly dipolar signal.

A high-resolution palaeoclimate record for the last 4800 years from lake la Brava, SE pampas plains, Argentina

Resumen Los cambios climaticos son reflejados en las variaciones de diferentes parametros. Las secuencias sedimentarias de lagos son buena fuente de esta informacion debido a que proveen grabaciones continuas y detalladas de cambios paleoclimaticos.Para determinar los cambios en el clima al SE de la llanura Pampeana, se presentan estudios de magnetismo de rocas realizados en un testigo colectado del fondo de la Laguna La Brava (Argentina). Tambien se midieron contenidos totales de sulfuro, carbon organico e inorganico (TS, TOC y TIC), elementos alcalinos, metales pesados y livianos, y cambios en las comunidades de vegetacion. Se realizaron cinco determinaciones de edades radiocarbonicas y se calcularon las edades calibradas. La tasa promedio de acumulacion de sedimento es 1.3 mm/ano y la secuencia representa los ultimos 4800 anos en edades calibradas (cal. BP).El objetivo principal fue reconstruir el balance M. A. Irurzun * C. S. G. GogorzaA. M. SinitoM. A. E. ChaparroInstituto de Fisica Arroyo SecoUniversidad Nacional del Centro de la Provincia de Buenos AiresPinto 399, 7000 Tandil, Argentina

Paleomagnetic and paleoclimatic investigation at Laguna Melincue (Pampean Plains, Argentina): preliminary results

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.