Oligocene swamp sediments of Lesvos Island, Greece (geochemistry and mineralogy)

Abstract

The Tertiary Lapsarna swamp sedimentary rocks include thin horizons (organic-rich sediments, up to 22% Corg). Analyses of major elements of carbonates, shaly and siliceous rocks, and a thin, intensively silicified coaly horizon were taken (10 representative samples). Pure carbonates consistalmost completely of calcite, the siliceous sediments of quartz and calcite, and the shales of montmorillonite, feldspar, quartz, dolomite and calcite. The shales contain montmorillonite as the only clay component. The presence of montmorillonite in all shales suggests that the chemistry of the clay-forming solutions lies within the stability field of montmorillonite. Geochemical data indicate that montmorillonite and associated immobile elements (La, Zr, Y, Nb) are the products of hydrolysis of volcanic material in a subtropical region. The intense silification of the coaly horizon is due to a contact with silica-rich solutions that formed during the formation of montmorillonite. Quartz is produced diagenetically by transformation of amorphous opal-A after burial. © 1992 Institut für Paläontologie, Universität Erlangen