An example of sedimentary filling in the chalk karst of the Western Paris Basin: Characterization, origins and hydrosedimentary behaviour, 2004, Laignel B. , Dupuis E. , Rodet J. , Lacroix M. , Massei N. ,

The Petites Dales cave is a favourable site for studying the sedimentary fillings of the chalk karst of the Western Paris Basin. Our study is based on the lithological characterization of karstic sediments and mineralogical and chemical comparisons between these sediments and the likely sedimentary sources (insoluble residue of chalk, clay-with-flints, loess). Our results show that there are three main families of sediment in the Petites Dales karst: brown clayey silts, beige silts, pale beige silts. The karst sediments essentially originate in the mechanical erosion of loess. The insoluble residue of chalk, coming from the chalk weathering, is only located in the brown clayey silts, and constitutes a weak amount of this sediment type. According to these results, we propose three conceptual models of hydro sedimentary behaviour of the Petites Dales karstic system that could have resulted in such an intra-karstic deposition sequence

INCIDENCES OF THE TECTONICS IN THE KARSTIFICATION OF CHALK LIMESTONES IN THE WESTERN PARIS BASIN: EXAMPLE FROM THE PETITES DALES CAVE (SAINT MARTIN AUX BUNEAUX, FRANCE), 2013, Rodet J. , Ma K. , Viard J. P.

 

The classical approach to study the karstification attributes a major role to the structure in the establishment of concentrated drainage of groundwater. This structure, essentially tectonics and stratigraphy, serves to guide the water, which gradually opens up these discontinuities to build a network, from the introduction to the resurgence. This too idealistic view does not reflect the complexity of the establishment of a karst system. Indeed, experience shows that some bedrocks contain karst drains in the absence of any cracking. What’s more, some conduits can go through the structural elements without undergoing any morphological changes. In the chalk of Western Paris Basin, the Petites Dales Cave proves an excellent observatory. We have conducted a study on the relationship between the main conduit, restitution collector of the underground system, and observable fissures in the roof and walls of the conduit. Along a drain of 421 m, we counted 374 fissures, the total length of which being a little more than 867 m. Examination of the orientation of the drain and fissures reveals four types of relationship: (1) parallel (2) oblique, (3) perpendicular and (4) no joints. No correlation could be established between the development of the collector and the presence of fissures, other than very occasionally or during episodes of overflow. In fact, the relationship between fissure and karstic conduit cannot be established, therefore it is necessary to introduce other factors in the speleogenesis, such as porosity of the chalky bedrocks, and the direct effect of the hydraulic gradient.