Increasing Diagenesis of Clay Minerals in Isochronous Levels of Valanginian Limestone-Marl Alternations of the Vocontian Trough. Geographic Zonation.

Increasing Diagenesis of Clay Minerals in Isochronous Levels of Valanginian Limestone-Marl Alternations of the Vocontian Trough. Geographic Zonation. Development of Serge Ferry, Michel Rio and Pierre Cotillon, represented Georges Millot. Magazine National Academy of Sciences. Paris, Series II, ¹ 297 from July, 4 1983.

    In Valanginian cyclic deposits of the Vocontian Trough (French Subalpine Ranges), strong differences have been found in clay assemblages of ten pelagic limy beds and ten marly interbeds traced over the whole basin. Percentage maps of clay minerals clearly show that these changes are due to the superimposition of three factors acting mith variable intensity according to place: (1) inherited, climatically-controlled differences between the clays of beds and those of interbeds, (1) differential sedimentation which induced a first geographic zonation, and (3) thermal diagenesis which shifted eastward initial assemblages toward chlorite-illite associations, especially in limy beds.

    Explanation of picture

    Fig. 1. — Geographic variation of clay mineral assemblages, within the limy bed number 10, as shown by percentage maps of each component: 1, present-day outcrops of the crystalline basement; 2, sampled sections; 3, overthrusts; 4, limit between hemipelagic limestone-marl alternations of the outer platform (striped) and pelagic counterparts of the Vocontian trough (in white); 5, supply directions of kaolinite; 6, percentage curves.

    

    Explanation of picture

    Fig. 2. — Geographic variation of clay mineral assemblages within the marly interbed number 8-9, as shown by percentage maps of each component.