BEDDING ASSOCIATED TO THE DYNAMICS OF STONE-BANKED SHEETS IN AN ALPINE ENVIRONMENT (LA MORTICE, SOUTHERN ALPES, FRANCE)

Bedding associated to the dynamics of stone-banked sheets in an alpine environment (La Mortice, southern Alpes, France). This paper emphasizes the role of stone-banked sheets in bedding of slope deposits at La Mortice (3170 m). Coarse particles sorting due to frost heaving and runoff occurs within sheets leading to the development of stone banks and surface pavements in connection with matrix-rich beds. Burying of stones at the sheet front by the frost creep induced movement of matrix-rich layers makes it possible the formation of coarse openwork beds. Cryoturbation, heaving of blocky materials and intense leaching of fine particles through the different beds disturb the stratification. A comparison between deposits from the east and the northwest facing slopes of La Mortice and Andean examples clearly shows that bedding is better developped when superficial freeze-thaw cycles are frequent and the depth of seasonal freezing shallow.