Effects of environmental change on scree slope development throughout the postglacial period in the Chic-Choc Mountains in the northern Gaspe Peninsula, Quebec

The combined study of present-day processes and stratigraphic data, has per mitted the reconstruction of the dynamics of scree slopes of the northern G aspe Peninsula throughout the postglacial period. In this region, liberated progressively from beneath an ice cover between 13,500 and 10,000 years BP , the scree slopes have to be seen as an integral part of a regional geosys tem. Evolution of these slopes has been rapid, influenced by local paraglac ial conditions (glacio-isostatic rebound, glacio-eustatic fluctuations, and re-equilibration of glacially over-steepened rockwalls) which operated aga inst a backdrop of Late Glacial and Holocene climatic fluctuations. During the Younger Dryas and part of the Early Holocene period, as the foot slopes emerged from beneath the Goldthwait Sea, the basal part of several scree s lopes advanced onto marine terraces as lobate rock glaciers, under the infl uence of a periglacial climate, characterised by permafrost. Many scree slo pes continued to transfer debris downslope after regional establishment of a closed forest cover at ca. 7250 years BP. Forest colonisation in the earl y pre-emergent phase of the postglacial period was retarded, due to constan t replenishment of the debris removed from the foot slopes by marine proces ses. In the later post-emergent phase, development of a complete forest cov er has only been possible on slopes where the summit rockwall segment has b een completely eliminated, a condition not yet fulfilled for many geomorpho logically active scree slopes of the region. In fact, both of these paragla cial influences have been diachronous on a regional scale. Advance upslope of the forest front on the scree slopes appears to have been slow, difficul t and subject to periodic regressions of possible climatic origin, as indic ated by numerous buried soils in colluvial stratigraphic sequences, and for the past 150 years by dendro-ecological studies. Stratigraphic exposures, along with direct observation of slope events, have revealed the operation of a large variety of debris transfer processes, including niveo-aeolian se dimentation and frost-coated clast flows, the latter representing an import ant process first recognised on the scree slopes of Gaspesie. (C) 2000 Else vier Science B.V. All rights reserved.