Exhumation de sols polygonaux et dégradation de la pelouse d'altitude sur le Pla de Gorra Blanc (2.450 m). Massif du Puigmal - Pyrénées méditerranéennes

摘要

Summary. Under the high altitude grass of « Gorra blanc » Pla, polygonal soils dating from the cold phases of the Quaternary period can be observed. This ancient configuration is revealed by the presence of apertures in the argillaceous central part and of traces of alpine clover on the bigstoned divisions. Tufts of plants and straggling grass have superseded the dense, boreo-alpine grass implanted during the Atlantic Optimum. This degradation has allowed, deep down, the starting of movements of geliturbation. The risings of clay are revealed on the surface by the presence of argillaceous or humiferous apertures. Trifolium alpinum can only survive away from those elevatory apparatus. A complete transformation of the ancient polygonal structure corresponds to a more thorough stage of exhumation.