Geothermal history of the Carboniferous in South Limburg, the Netherlands

The geothermal history of Upper Carboniferous rocks in the former mining district of South Limburg (the Netherlands) is complex. Maturity modelling as calibrated by vitrinite reflectance measurements and volatile matter content shows that the present-day coalification patterns of the Carboniferous were established in Late Westphalian to Early Permian times. Variations in the degree of coalification were mapped using as a reference level the upper Westphalian A coal seam GB 23. Modelled burial and thermal histories for the area indicate that regional variations in overburden, heatflow and in timing of thermal events in front of the Variscan orogen caused the spatial variation in coalification. In the southern part of the area, differences in overburden combined with a generally high heatflow determined the coalification patterns. In the northeastern part of South Limburg an additional thermal event, related to a Permian(?) intrusion, overprinted the earlier coalification pattern. The coalification data are consistent with basement heatflow values during the Carboniferous in the order of 46 to 71 mW/m2 and erosion following the Variscan orogeny of some 2900 m of sediments around Sittard and as much as 5400 m in the southeasternmost part of South Limburg.