The probable succession of morphological phases during a Quaternary climatic cycle in Upper Belgium
DOI:
https://doi.org/10.26485/BP/1960/9/8Keywords:
morphological phases, Quaternary climatic cycle, BelgiumAbstract
Article in French.
ORIGINAL TITLE: La succession probable des phases morphologiques au cours d'un cycle climatique quaternaire en haute Belgique
Observations regarding Quaternary climates and morphological evolution become now numerous in High Belgium and call for a first critical examination, especially as regards the formation of „stability" terraces.
- Cryergic periods seem to coincide, in the main valleys and along brooks with gentle slope, with a notable slackening and even stopping of vertical erosion, followed then by a rejuvenation (,,pediments" or erosion surfaces moulded by the combined work of frost and solifluction, graded in relation with the top of the terrace deposits; superimposed brook or gully on the valley-side of the former through the rock waste). Time elapsed between the solifluction phase and the renewed down cutting would be small enough to avoid modification of the river course, which is ruled by the solifluction deposits coming down on the bottom of the valley. In the middle course of the brooks, asymmetrical valley betokens simultaneous action of solifluction and vertical erosion: both phases cannot be distinguished in such a case.
- The lack of concordance between relief features appeared after the solifluction phase and the weak power of the present running water imply the presence of a transition phase (rain-wash phase). The criteria for estimating the eroding power (not working runways under forest, underfit meanders, precocious senility of some brooks) have to be used with carefulness.
- Between the comparatively quiet phase of temperate climate and the coming back cryergy, a second rain-wash phase seems to occur, but its effects may seidom be checked (truncated soil profile overlain by eoarse and flat lying sediments, residue of the sorting of the upper part by running water, fossilized itself by solifluction deposits). Therefore, the most complete climatic cycles would comprise four phases at least. It remains to study further details of their morphological effects in each part of the hydrological basin (valley-side, valley-bottom of brooks, and then of streams). If well used, this starting schema would make easier research as regard originality of each cycle.
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