Sur la vitesse d'évolution au cours du Quaternaire de quelques formes karstiques superficielles

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Abstract
On the speed of the evolution of some superficial karst forms in the course of the quaternary. The notion of eroded outcrop, expressed in mm per 1,000 years and calculated on the rate of flow and the average quantity of carbonates present, meets not only with the difficulty of establishing it, but also that of geomorphological interpretation : the respective parts of the superficial dissolution and of subterranean dissolution, passing through the time-scale of the quaternary extrapolation becomes increasingly doubtful. The study of limestone paving, exposed to dissolution from a precise date (monuments and quarries, glacial-polished stone, limestone stumps scattered on the Flandrian basin) shows that there is great variation in the speed of superficial dissolution, the predominant role of the variations in porosity and microfissuration in the genesis of the various types of rock. Estimating the speed of the evolution of dolines is even more problematical. One has to distinguish between monogenic dolines, whose evolution took place under a constant climate, for example, the small snow-melt dolines, and polygenic formations, dolines and ouvalas, which represent the cumulated effect of various phases of evolution.

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