Reconstruction of Late Paleozoic heat flows and burial histories at the Rhenohercynian-Subvariscan boundary, Germany

The thermal and burial history of the Herzkamp syncline, located in the tra nsition zone between the Variscan Rhenish Massif and the Ruhr foreland basi n (western Germany), was reconstructed using PDI/PC-1D-basin modelling soft ware (IES), The models were calibrated with new vitrinite reflectance data measured on Palaeozoic outcrop samples. High sample density and quality of the calibration data allowed a 3D reconstruction of the heat flow as well a s of burial and erosion history. Vitrinite reflectance values range from 0. 8 to 4.9%R-r and generally increase with increasing stratigraphic age. The coalification pattern confirms pre-tectonic maturation, especially in the w estern part of the study area. A "low-coalification zone" showing stagnatin g/decreasing coalification with increasing stratigraphic age exists, howeve r, northeast of the Ennepe thrust, indicating synorogenic coalification. Th is anomaly is explained by early thrusting in the northern Rhenish Massif r esulting in restricted burial/early uplift and thus lower thermal maturity. One result of numerical modelling is that palaeo-heat flows during maximum burial (Westphalian or post-Westphalian) decreased southwards from approxi mately 65 to less than 50 mW/m(2) Maximum burial depths for the base and to p of the Namurian also decrease southwards from 7000 to 3600 m and 4600 to 1800 m, respectively, resulting in southwards-decreasing coalification of t he respective stratigraphic horizon. Eroded overburden increases southwards (3100-5700 m), with the exception of the low-coalification zone, which is characterised by lower amounts of eroded overburden (1300-2900 m) and an ea rlier onset of erosion, i.e, in the Westphalian B rather than Westphalian D or post-Westphalian.