Origin and thermal maturity of the organic matter in the Lower Palaeozoic rocks of the Pomeranian Caledonides and their foreland (northern Poland)

Abstract

The clayey-muddy complex of the Ordovician and Silurian age in the Pomeranian Caledonides belt as well as the Cambrian, Ordovician and Silurian rocks at its foreland (the East European Craton) contain the same genetical type of the organic matter dominated by the syngenetic sapropelic material (oil-prone). The intensity and character of the thermal alterations in both stable organic matter mobile components show distinct analogies despite the different tectonic involvement of both regions. The reflectivity index of the vitrinite-like minerals shows an increase with a burial depth of the successive members of the Lower Palaeozoic. The local increase in thermal alteration of the organic matter is related to the zones of the increased tectonic activity. Assuming that the maximum burial depth of the studied sediments corresponds to their present depth, it can be concluded that the thermal palaeogradient for the Early Palaeozoic in the Pomeranian region was higher than the present-day one. The range of maximum palaeotemperatures which influenced the Lower Palaeozoic complex is very wide ranging from about 70 to 200ºC in the Caledonian zone. The analysed deposits do not show a good quality as potential source rocks for hydrocarbon generation. Their low generation potential is probably caused by an earlier generation of a part of hydrocarbons.