Abstract
The physico-chemical and mineralogical study of the Ara river sediments, in the Central Pyrenees (Spain), allows to recognize the genesis and evolution of its basin. The minerals of the sand fraction, the ones corresponding to the clay fraction and the minority elements, reveal certain processes and associations that, in addition to the identification of the fluvial terraces, fans, glacis and even morainic deposits, contribute to explain the geological history of the Central Pyrenees, the main objective of this work. The application of a multivariate factorial analysis to the data with BMDP-4M program was very helpful for the interpretation of the results. The more resistant minerals are found in the thinner textural fractions, whereas the more alterable are located in the thicker fractions. The cones and glacis, composed by materials of the flysch, reveal an alteration of the carbonated materials which is shown by the formation of feldspars and anphybols. The formation of iron and manganese metal oxides, of different crystallinity degrees, associated with chrome, lead and nickel, is also observed. The morainic deposits, mainly composed by silicate materials, bring along the formation of illite associated with copper and zinc. Finally, the fluvial terraces have a combination of both alteration processes previously described.
Highlights
The purpose of this paper is to study the river Ara in the Central Spanish Pyrenees, assessing the characteristics of the open valley areas, where the river has a large capacity of sediment accumulation asuch as gorges and canyons, which are much more active as far as erosion and dragging is concerned. Is evident that it is in the wide stretches of the river where there are best represented the various levels of the river terrace (HERNÁNDEZ, 1991; HERNÁNDEZ & RUBIO, 1990) and for this reason many of the samples used were collected from these zones, we have studied the flood plains, the present sand bars and deposits
The interpretation of the results seems to show that carbonates appear correlated with sand, in the area under study, carbonate is associated with the coarse textural fraction, while clay is linked to quartz, which proves its relationship with finer fractions
The application of minéralogie analysis, chemical and statistical methods to certain sediments of the Ara river (Central Pyrenees, Spain) allows to achieve a wider knowledge of the processes of alteration and genesis of superficial formations, which are present in the basin
Summary
The purpose of this paper is to study the river Ara in the Central Spanish Pyrenees, assessing the characteristics of the open valley areas, where the river has a large capacity of sediment accumulation asuch as gorges and canyons, which are much more active as far as erosion and dragging is concerned. Is evident that it is in the wide stretches of the river where there are best represented the various levels of the river terrace (HERNÁNDEZ, 1991; HERNÁNDEZ & RUBIO, 1990) and for this reason many of the samples used were collected from these zones, we have studied the flood plains, the present sand bars and deposits (fans, glacis, etc.).
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