Influence de la diagenèse d'enfouissement sur l'homogénéisation isotopique K-Ar des illites: exemple du Jurassique-Crétacé du bassin d'Agadir, Maroc

The clay assemblages of the Late Jurassic-Early Cretaceous sediments of the Agadir Basin are affected by burial diagenesis. Apparent ages of these formations, from the K-Ar dating of fine grain size fractions (< 2 μm), decrease downward. This indicates an opening of the K-Ar isotopic system of detrital Hercynian minerals during burial. The extent of the isotopic rehomogenisation is more important in sandstones than in clayey marl facies. During burial diagenesis, a temperature of 165°C in clayey marl and 110°C in sandstone can be enough for isotopic rehomogenisation of fine-grained Hercynian illite. The migration of pore water seems to favour the diffusion of radiogenic ⁴⁰Ar in sandstones.