Méthodes et éléments de cartoqraphie d'un paléokarst. L'exemple de la Carrière du Clypot (Hainaut, Belgique)

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Abstract
Mapping of a palaeokarst : The example of the " Clypot " quarry (Hainaut Province, Belgium). Palaeokarsts have been often considered like geological objects different from the present karstk systems which can be explored partially by speleological ways. But it is obvious that their genesis have not been different from the genesis of the neogense karstk systems, in same environnemental conditions. The study of palaeokarsts has a great importance for the comparison with present systems. Moreover, they conserve continental sediments which generally disapeare, but with possility of dating by marine trangressive series wich cover the palaeokarsts or by absolute dating like Kar or Ar-Ar on glauconite or ferriferous illite. We present here an interesting example of palaeokarstic features in a quarry where the works permit to map those features. This map constitues the basis for future studies ; it has shown different types of morphological features and deposits, their geometrical relations and their genetic links. We have (i) ghosts-rocks and pseudo-enkarsts which result from the alteration in situ of the host-rock with formation of residual alterite. Those features organise like linear channels along tectonic fractures. Some channels can joint together in great "pockets". At the summit of the limestone formation, (ii) palaeo-lapiaz devebps under the transgressive cover where we find pebbles and sands. Finally, (iii) endokarstic galleries can come from an autonomous hollowing (" classical " karst) or from old ghost-rocks which become partially empty by a new hydrological activity.

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