Thin-section petrography of pelites, a promising approach in sedimentology

Abstract

Pelites are described mainly by their macroscopic appearance, X-ray diffraction mineralogy and chemical composition. However, these conventional methods are being increasingly supplemented by thin-section analysis. Even so-called soft-cuttings aggregates can be successfully studied in thin section after appropriate impregnation. Only by integration of the various analytical methods can pelites be fully characterized in terms of original grain size and mineralogy, present mineral composition, sedimentary fabric and history of diagenetic alteration. Thin sections of pelites from various stratigraphic levels in the FRG are briefly described: Lower Carboniferous bedded cherts, siliceous shales and tuffs; Upper Jurassic marlstones; Lower Cretaceous claystones, siliceous marlstones and tuffs; Messel oil shale (Eocene) and Eocene tuffs; Oligocene clays and tuffs. In pelites diagenetic processes such as resorption diagenesis transform the original mineral composition and alter the original sedimentary grain-size distribution. The immense diagnostic value of sedimentary as well as tectonic fabric can be exploited only by means of thin-section analysis.