MINERALS IN THE TR IASS IC SANDSTONES OF THE

• Main Authors: Bas Ins, The D Iagenet, Ic H Istory, Of Clay, J. R. Mossmann, N. Clauer, N. L Iewig
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1991
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.608.1102; http://www.minersoc.org/pages/Archive-CM/Volume_27/27-2-211.pdf

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. During diagenesis of sedimentary rocks, the minerals, fluids, organic matter and porosity evolve toward a steady state with respect to the physical and chemical conditions of the local environment. The prime parameters which determine the alteration can be classified into: (1) those inherent o the sediment itself such as its mineralogy, composition of organic matter, fluid chemistry, and the geometry and nature of the pore system, and (2) those that are imposed on the sediment such as pressure, temperature, and duration of the events. Al l these parameters can be measured and/or estimated by routine methods. However, precise