Processus et intensité actuelle et holocène de l'érosion du marbre de Grenville, région de Gatineau-Lièvre, Québec.

Abstract

Limestone tablets placed in various aquatic environments yielded a mean rate of erosion of 22,8 mm/1000 years. Within different soil media, the same method gave a 12,4 mm/1000 years intensity of erosion. The hydrochemical approach gave a mean rate of 21,4 mm/1000 years, but the median rate of 17,2 mm/1000 years is believed to be closer to reality. The karsts developed on the crystalline (metamorphic) limestone of the study area are found at the surface as well as underground. Fossil caves hang on the valley slopes far from the actual streams. Many active caves show in their path fossil phreatic tubes superimposed on active vadose corridors. Rates of erosion topographic position, and the sediment filling of the fossil caves, suggest that these could be pre-Holocene in age. One model implies a sub-glacial dissolution by meltwater (phreatic tube) and a subsequent Holocene erosion (vadose corridor). The second model implies a washing-away of sediments by glacial meltwater within a pre-holocene cave, followed by Holocene erosion. (Abstract shortened by UMI.)