Diagenetic relationships between sulphur species and formation of pyrite in coals and sediments

Abstract

Based on the abundant minerals in a Miocene freshwater sequence of mixed sediments (pieces of coal in clays, sand-stones and shales) alternating with coal layers, the following main sedimentation environments were distinguished: illite-montmorillonitic (I-M), calcitic (Ct) and coal-forming environment. Applying factor analyses to 16 geochemical parameters, an environmentally- specific early diagenetic connection between the sulphur transformation processes, amount of Corg and precursor material species (C27-C29-steranes) was determined. It was found that the effects of limiting factors on Spyr formation depended on the hydrogeochemical conditions of individual sedimentation environments. Pyrite formation in coals depended directly on participation of higher plant precursor materials and/or on the total sulphur content in the system. In the MS, pyrite formation directly depended on total sulphur content, hydrogeological conditions and the amount of Corg.