An investigation, using the chalk karst of Haute-Normandie (France), as an example of the relationships between the surface and endokarst using a granulometric method, 1998, Lacroix M. , Leboulanger T. , Wang H. Q. , Feeny V. , Dupont J. P. , Meyer R. ,

Karst, by definition, is the result of rock dissolution. Ii the rock is not completely soluble, residues will remain ('acquired' particles). This insoluble material, present in the springs issuing From the karst body after some time lag, provides information regarding karst processes taking place within the rock body. The presence of pathways between the surface and the endokarst is reflected by an increase in the suspended particulate material (SPM) that may be considered to be 'inherited' from outside of the karst system, By the study of microgranulometric spectra the origins of the particles are differentiated and, on this basis, a classification of karst systems is proposed. The technique was applied to the chalk karat of Haute Normandie (France) by obtaining characterisations of the microgranulometric fraction of the main surface formations (clay-with-flints and loess) and that produced by dissolution of the chalk. By the comparison of these spectra with those of the SPM contained in ten karst springs, it was possible to define two types of karsts ('open' and 'closed') and their intermediates. In 'closed' karst a majority of the particles originated from the dissolution of the chalk itself, while in the 'open' karst, the majority of the particles are derived from the surface formations. This notion of 'aperture' is quite different from the conventional allogenic/authigenic karst classification which implies the formation of an impermeable residual soil that focuses surface water inputs

Mise en evidence des relations surface-endokarst par la microgranulometrie, exemple du karst crayeux haut-normand, 1998, Lacroix Michel, Leboulanger Thierry, Wang Huaqing, Feeny Veronique, Dupont Jean Paul, Meyer Robert,

Karst, by definition, is the result of rock dissolution. If the rock is not completely soluble, residues will remain ('acquired' particles). This insoluble material, present in the springs issuing from the karst body after some time lag, provides information regarding karst processes taking place within the rock body. The presence of pathways between the surface and the endokarst is reflected by an increase in the suspended particulate material (SPM) that may be considered to be 'inherited' from outside of the karst system. By the study of microgranulometric spectra the origins of the particles are differentiated and, on this basis, a classification of karst systems is proposed. The technique was applied to the chalk karst of Haute Normandie (France) by obtaining characterisations of the microgranulometric fraction of the main surface formations (clay-with-flints and loess) and that produced by dissolution of the chalk. By the comparison of these spectra with those of the SPM contained in ten karst springs, it was possible to define two types of karsts ('open' and 'closed') and their intermediates. In 'closed' karst a majority of the particles originated from the dissolution of the chalk itself, while in the 'open' karst, the majority of the particles are derived from the surface formations. This notion of 'aperture' is quite different from the conventional allogenic/authigenic karst classification which implies the formation of an impermeable residual soil that focuses surface water inputs

Microgranulometric approach to a chalk karst, western Paris Basin, France, 2002, Lacroix M. , Rodet J. , Wang H. Q. , Laignel B. , Dupont J. P. ,

By definition, karst is the result of dissolution, and if the rock is not completely soluble, residues will remain ('acquired' particles). These insoluble residues provide a history of karstic activity and can be found in the outflows after a possible storage period in the endokarst. A direct connection, even if temporary, between the endokarst and the surface is reflected by the contribution of particles, which are referred to as 'inherited'. We have studied the chalk karsts of Haut Normandie by comparing microgranulometric spectra of suspended matter (SM), in subterranean waters and in solutions of the main surface formations (Clay-with-Flints Complex (CFC) and loess) and the Chalk dissolution products of all local stratigraphic levels. Based on these microgranulometric spectra, we propose a conceptual model for processes occurring in chalk karsts and a classification scheme for karstified systems according to how such systems deal with particles. In a 'closed' karst, the suspended matter tends to come from the Chalk itself, while in the case of an 'open' karst, the majority of suspended particles comes from surface formations. This notion of 'openness' differs from the currently used categorization into allogenic and autogenic systems, which depends upon an impermeable cover concentrating the infiltration. (C) 2002 Elsevier Science B.V All rights reserved

Assessment of direct transfer and resuspension of particles during turbid floods at a karstic spring, 2003, Massei N. , Wang H. Q. , Dupont J. P. , Rodet J. , Laignel B. ,

Turbid water can be the source of important sanitary problems in karstic regions. It is the case of the Pays de Caux, in Haute Normandie, where the main resource in drinking water is provided by the chalk aquifer. In the case of the typical binary karst of the Pays de Caux, turbidity results from the input in sinkholes of turbid surface water induced by erosion on the plateaus. At some spring tappings, water may be very turbid in period of intense rainfall. The turbidity observed at a karstic spring is a complex signal which contains a part of direct transfer and a part of resuspension of the particles being transported. The aim of this study is turbidigraph separation, which would permit to distinguish the direct transfer and resuspension components of the turbidigraph. These two components are separated by comparing the elementary surface storm-derived water fluxes and elementary turbidity signals at the spring. The procedure takes place in three phases: (i) spring hydrograph separation by means of a two components mixing model (surface water and karstic groundwater) using specific electrical conductivity, (ii) decomposition of storm-derived water flux and turbidity thanks to the second-derivative method, (iii) comparison of the transfer times (approximate tomodal times) of the elementary turbidity and surface water flux signals, respectively. The mass corresponding to direct transfer, computed after signal decomposition, is then used to re-calculate a particle recovery rate, which passes so from 514 to 373%. Relations between particle flux and hydrodynamics show that resuspension can be either the fact of the dynamics of the introduction system, or that of the chalk karstic aquifer in general (case of resuspension not associated to surface water flux). In this sense, evolution of particle flux (and consequently of turbidity) can be also a marker of the karst structure. (C) 2003 Elsevier Science B.V. All rights reserved

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