QUANTIFICATION OF LOSS OF CALCITE, PYRITE, AND ORGANIC-MATTER DUE TO WEATHERING OF TOARCIAN BLACK SHALES AND EFFECTS ON KEROGEN AND BITUMEN CHARACTERISTICS

Comparison of geochemical data on Posidonia Shale (Early Toarcian) from a shallow unweathered core and from adjacent weathered exposures of the same facies was performed. Results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering. Due to this process of weathering, the bulk composition of organic matter, especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles, are changed. Estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution.