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A B S T R A C T: Rhaetian (Upper Triassic) sandy horizons were sampled from the Paris Basin from SW to NE, crosscutting the Rhaetian at different depths from outcrop in the NE to 2700 m in the centre of the basin. The smallest clay sub-fractions (<0.2 /~m) from the deepest samples consist mainly of illite and chlorite having a K-Ar age of -190 Ma. Both minerals probably formed under specific hydrothermal conditions at high temperature, but at a burial depth of only 500 m. This thermal event could represent an echo of the "crustal" breakdown of the Northwestern European craton during the opening of the North Atlantic Ocean. Two other generations of illite-smectite mixed-layers formed in the same Rhaetian horizons at somewhat lower temperatures about 150 and 80 Ma ago. The three generations of clay minerals could be characterized and dated because of combined mineralogical, crystallographical and morphological data supporting the dating attempts.

Genetically homogeneous clay fractions are not always available for K-Ar isotopic dating of authigenic sedimentary material, particularly when dating illitic mixed-layer clay minerals. Three populations of mixed-layer clay minerals have been recognized in Upper Triassic sandstones from the Paris Basin (France), their occurrences being related to the flow of allochthonous fluids across the stratigraphic sections of the basin during Mesozoic times. A method is described for interpreting the K-Ar mixture ages obtained on carefully selected fractions, resulting in constraints being able to be made on the timing of the movements of these fluids.

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Centre Naiional de Recherche sur les Sites et Sols Pollucs (CNKSSPi. Douai Cede.x. Fiance Polycyclic atoniatic hydrocarlMius iPAlLs} ttre the must conwionty ftnnul piilltiiants in fot tner coke site grounds. These organic pollutants are particularly a concern hecau.se of their possible to.xic. catvinogenic or tiuttttgenic properties. Hiodegradation is one possible pathway for PAIIs elintinationfroin .wils.This study aims to evaluate intrinsic degradation potential of PAIIs in soils taken from twofornter coke sites, differing by their conlatninatioti levels aiul hy their physico-chemical characteristics {organic carbon and metal cotitenix).PAHs hiodegiadation kinetics as obsen'ed in hoth soil types clistitiguisht's between Aiv> .