CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Clay mineral associations in modern stream sediments of the Paraná River tributaries (Argentina)
Autor/es:
MANASSERO, MARCELO; CAMILIÓN, CECILIA; POIRÉ, DANIEL G.; DA SILVA, MARIO; RONCO, ALICIA
Lugar:
Buenos Aires
Reunión:
Congreso; XII Reunión Argentina de Sedimentología; 2008
Institución organizadora:
Asociación Argentina de Sedimentología
Resumen:
The fine grained fraction of the stream bed sediments (upper 20 cm) from equivalent distal positions of different fluvial basins discharging into the Paraná River was analysed and compared using standardised methods for grain size determination, sand and clay mineral composition. The sand fraction is mainly composed by stable minerals that resist weathering and transport, like quartz (90%) with minor amounts of chalcedony, potassium feldspar and plagioclase. Heavy minerals are rare (2%) and are composed of magnetic and non magnetic opaque minerals. The analysis of 35 loose and very fine sand bottom sediment-samples by optical microscopy is coherent with this data, showing also the input of quartzose sources manly from the Brazilian Shield and also, that glass-shards sources are spread not only in the Pampean plains but in the Andean Cordillera as well. Besides, Marengo et al., (2005), have shown that glass shards tend to have a small preservation potential. The analysis of grain size data from cores and statistical parameters of the core samples show that most of the samples have a bimodal pattern, with main frequencies both, in the coarse (silt or fine sand) and finer fractions (clays). The mean grain sizes vary from very fine sand (3-4 phi) to very coarse to coarse silt (5-6 to 4-5 phi) with poor to moderate sorting (standard deviation), high kurtosis and positive skewness (see also Manassero et al., 2004). The grain size data from the samples of the Paraná River tributaries do not show strong differences and they suggest typical and prevailing fluvial sedimentary processes with well defined rolling-sliding, saltation and suspension populations, according to important changes in the hydraulic regime. Three different clay mineral assemblages are detected in these mud-sandy bottom sediments. A kaolinitic association, with sources areas in the Upper Amazon to the north-east of the study area and within the Brazilian Shield (also with subordinated crystalline illite); an illite-smectite association, coming from the Andean Cordillera and the Chaco plains in the north-west and mainly represented by the Paraguay, Bermejo and Pilcomayo rivers (see also Bertolino et al., 1991, Bertolino & Depetris, 1992); and the third southern illitic dominant, but with lower cristallinity index than in the northern area, with source in the Pampean plains to the West of Argentina. Mixed layer clays illite/smectite were also detected in this southern sector. These clay mineral associations reflect not only the climate but the source rock composition, respectively, in these three main geographical areas. Along its course, the Paraná River tends to homogenize this clay mineralogy into a single illitic-smectitic association, eroded and transported from all these source areas. In this contribution, three main clay mineral associations (illite-chlorite, smectite-I/S, and kaolinite) in stream sediments of the Paraná River and tributaries within a wide area of Argentina are described and their provenance is interpreted on the basis of controlling factors, climate and provenance. et al., (2005), have shown that glass shards tend to have a small preservation potential. The analysis of grain size data from cores and statistical parameters of the core samples show that most of the samples have a bimodal pattern, with main frequencies both, in the coarse (silt or fine sand) and finer fractions (clays). The mean grain sizes vary from very fine sand (3-4 phi) to very coarse to coarse silt (5-6 to 4-5 phi) with poor to moderate sorting (standard deviation), high kurtosis and positive skewness (see also Manassero et al., 2004). The grain size data from the samples of the Paraná River tributaries do not show strong differences and they suggest typical and prevailing fluvial sedimentary processes with well defined rolling-sliding, saltation and suspension populations, according to important changes in the hydraulic regime. Three different clay mineral assemblages are detected in these mud-sandy bottom sediments. A kaolinitic association, with sources areas in the Upper Amazon to the north-east of the study area and within the Brazilian Shield (also with subordinated crystalline illite); an illite-smectite association, coming from the Andean Cordillera and the Chaco plains in the north-west and mainly represented by the Paraguay, Bermejo and Pilcomayo rivers (see also Bertolino et al., 1991, Bertolino & Depetris, 1992); and the third southern illitic dominant, but with lower cristallinity index than in the northern area, with source in the Pampean plains to the West of Argentina. Mixed layer clays illite/smectite were also detected in this southern sector. These clay mineral associations reflect not only the climate but the source rock composition, respectively, in these three main geographical areas. Along its course, the Paraná River tends to homogenize this clay mineralogy into a single illitic-smectitic association, eroded and transported from all these source areas. In this contribution, three main clay mineral associations (illite-chlorite, smectite-I/S, and kaolinite) in stream sediments of the Paraná River and tributaries within a wide area of Argentina are described and their provenance is interpreted on the basis of controlling factors, climate and provenance.