La grotte du Portel ouest (Loubens, Ariège) : nouvelles données stratigraphiques par l'étude de la susceptibilité magnétique Portel ouest cave (Loubens, Ariège) : New stratigraphical data from a magnetic susceptibility study

摘要

The variation of the magnetic susceptibility recorded in each layer in the Portel cave shows a good correlation with the sedimentological analyses and also with the evolution of the composition of the faunal associations and their palaeoenvironmental significance on the northern edge of the Ariege Pyrenees during the Middle Palaeolithic. This study reveals the presence of several layers with different magnetic properties. The high values of magnetic susceptibility and its frequency dependence and the ratio IRM-100/SIRM are the result the abundance of non-detrital iron oxides (produced from primary iron oxides by physico-chemical processes). These oxides are very fine-grained, they have a low coercive field and saturate in a weak magnetic field. The percentage of supermagnetic grains increases with the clay content (climatic improvement), and decreases in the more sandy, less clayey layers (climatic deterioration).