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Distribución y origen de sedimentos loessicos superficiales de la pampa norte en base a la mineralogia de arenas: Resultados preliminares

Keywords: northern pampa, loess, soils, sand fraction, mineralogy.

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Abstract:

mineralogical information about the sand fraction (62- 246 μm), available at the institute of soils of inta-castelar, was analyzed by selection of 92 representative samples of deep (bc or c) horizons of soils from the northern pampa region developed on loessic materials. on the basis of the observed quantitative variations and their common usage as sedimentological indicators, four mineralogical parameters were selected: quartz / feldspar + glass index; % heavy minerals; % pyroxenes; and % micas (table 1). these parameters were then used to differentiate and cartographically group the data into sectors using prior information in the literature and statistical techniques (figures 1 to 4). finally a map was developed that integrates the information for the surficial sediments (figure 5). area a, located in the western portion of the region, occurs north of buenos aires, southwest of santa fe, and south east of córdoba. this area is characterized by a high relative proportion of volcanic glass and feldspars [index (q / f + v).100, less than 30], a high content of pyroxenes (more than 16 %), and a high percentage of total heavy minerals (more than 12 %). a strip towards the east that borders the paraná river and the de la plata river is characterized by higher proportions of quartz and lower proportions of pyroxenes and heavy minerals than the soils in area a. furthermore the differences observed in the proportion of micas within this strip, which borders the fluvial axis, can be differentiated into two areas. in the first one northeast of buenos aires, area b, the percentages of mica are relatively low (less than 7 %) and similar to those in the area a. conversely, an area southeast of santa fe and a small part ne of buenos aires, area c, has a markedly higher proportion of micas (more than 7 %) than area b. the mineralogical association dominant in area a coincides in general with classical pampean loess that has been characterized by several authors. the high proport

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