Upper Carboniferous source rocks north and south of the Variscan Front (NW and Central Europe)

Abstract

Some topical aspects of Upper Carboniferous source rocks within the three main tectonic settings in NW and Central Europe are described. These are likely to offer an effective tool for reduction of risk in future exploration. In the foreland, the main geological factors responsible for the nitrogen content of gas accumulations and for the isotopic composition of methane are outlined. It will probably be possible to predict the molecular and isotopic composition of gas accumulations in the future. In addition, the application of the dynamics of diffusion processes to the loss of gas accumulations over geological time offers the possibility of predicting hydrocarbon fill in some areas of the basin. In the Variscan fold belt, the model of thin-skin tectonics suggests that the lowermost, parautochthonous low rank thrust sheets are more likely to be source rocks than are allochthonous, high rank thrust sheets. Additionally young subsidence is required in order to meet the conditions of gas dynamics. The possible source rock potential of the Permo-Carboniferous fills of the intramontane grabens south of the Variscan front are reported here for the first time. Some promising discoveries below the Swiss and German Molasse basin as well as in the eastern Paris Basin mean that the intramontane grabens are now an interesting exploration'objective.