[en] The 'Cran aux iguanodons' of Bernissart is a sinkhole (or chimney caving) with a valuable paleontological deposit due to the exceptional quantity and diversity of fossils found during the excavation conducted from 1878 to 1881. In fact, bones have been discovered in a clay geological formation when digging à mine gallery at the -322 m level of the 'Sainte Barbe' shaft of the 'charbonnages de Bernissart s.a.'. A subsequent extraction has then be undergone at the -322 m and -356 m levels, giving an overall production of 29 iguanodon's skeletons. Referring to the available data at the Natural Sciences Museum of Brussels where the found skeletons are exhibited, one does not know the real ratio of the volume of the excavated area with respect to the entire clay structure of the sinkhole.
In December 1998, tanks to a funding by IDETA (a technical association of the Mons's region municipalities), the mining engineering department of the 'Faculté Polytechnique de Mons' conducted a feasibility study of some exploration wells in the sinkhole. This study, which used a 3D computer model, was based on data from the 'Charbonnages de Bernissart' and the Brussels's museum. This showed that the clay seams contained in the sinkhole have been explored in a limited ratio (probably less than 10%) . This proves that one has a real chance of founding again a lot of fossils.
To gain a good knowledge on the real fossil content of the sinkhole the study showed that it was desirable to undergo some exploration wells of 400 m depth. A probability calculation based on the bone density (or concentration) obtained by the 1878 excavation yielded a result of 43 to 80 % of chance to cross a skeleton at least once, when using 4 coring wells. This result can be improved by geophysical techniques combined to coring operations.
Among the geophysical methods we chose one which seems to have a large potential of development due to the increase in the power of computers; this is the seismic or radar tomography between drillholes, but this second method is not suitable for clayey mediums.
Tomography methods are well known for shallow geological formations (depth below 100 m), and we believe that setting such techniques in a deep well crossing clayey materials will allow an acquisition of a valuable know-how which can be applied to other underground works. In fact, due to mine closing in Europe, the future management of underground resources (like coal) has to be done by methods which do not need a man presence at the mining face. For instance in the coal gasification process, tomography techniques can be developed to assess the shape and extend of the gasified area and then evaluate the production of a given coal.
