SETTLING OF CRYONIVAL STRATIFIED ROCKFALL IN THE GASPE PENINSULA (QUEBEC, CANADA) - ROLE OF NIVEO-EOLIAN SEDIMENTATION AND SUPRANIVAL SLIDES

Stratified talus deposits presently form in the cold temperate climate in pockets of the mixed forest of the Gaspe Peninsula. Repeated visits have allowed identification in detail of the processes responsible for their bedding. The main aspects addressed are: (a) main precesses involved in the bedding development, including post-depositional reworking (splash, percolation, summer talus shift); (b) diagnostic sedimentary properties of the deposits produced which allow recognition of the processes involved. Only the lower part of the talus cones shows stratification. Four type of deposits were found to overlie: (1) layers of fine argilite flakes deposited on snow during strong blizzards; (2) layers of medium to coarse sand derived from niveo-aeolian mantles accumulated by moderate winds; (3) layers of coarse openwork debris deposited on snow cover after supranival debris sliding; and finally (4) diamictic beds formed by supranival debris flows during spring thaw. There is no strict seasonality in the bedding. Transport of debris occurs principally at the snow surface. Consequently properties observable within sections result from snowmelt. Post-depositional surficial reworking by creep and splash processes also play a major role on the steeper part of the talus cones (> 30 degrees). The present-day evolution of these deposits in Gaspesie within a forested region (MAAT + 3 degrees C) shows that severe periglacial conditions are not required.