Résumé
The aim of this work is to analyze - through the prism of poljes - the development of karst networks and the organization of underground drainage in the case of plateau karsts. The methodology combines various approaches: i) surface morphology, ii) speleogenesis and iii) hydrogeology. The study site is the Loue basin, located in the french Jura Mountains. It is a typical plateau karsts, with its high karstification degree (around a hundred karst networks over 100 m, several karst springs with an average flow superior to 1 m3/s), and its extensive hydrogeological knowledge of karst hydrosystems (several hundred dye tracer tests available). First, a detailed surface morphological mapping has shown that the current plateaus correspond to ancient depressions with relatively flat, elliptical bottoms, and large extension (~ 400 km²). These plateaus are enclosed between the raised hydrological barriers of anticlines (fold systems). We interpreted these depressions as paleo-poljes. Currently perched 150 m above the base level, they only have a residual hydrological functioning, i.e. the lowest of them are subject to occasional flooding by exceeding the infiltration capacity of the ponors. Second, the analysis of numerous dye tracer tests within the largest karst hydrosystems has enabled us to determine their current recharge area. A strong spatial correlation between the geometry of the recharge area and the paleo-poljes suggests that the poljes plays a pre-structuring role in the organisation of the underground drainage. Third, the analysis of the horizontal galleries (relative altitude and endokarst forms) shows several significant levels and different speleogenetic processes (paragenesis, alteration) that can be linked to ancient local base levels contemporary of the hydrological functioning of the paleo-poljes (regular and long periods of flooding). Finally, our results enable us to propose a new conceptual model of plateau karsts in the Jura Massif, highlighting the role of poljes in karstogenesis and in the hydrogeological compartmentation of current hydrosystems.