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

Abstract

The thermal and burial history of the Herzkamp syncline, located in the transition zone between the Variscan Rhenish Massif and the Ruhr foreland basin (western Germany), was reconstructed using PDI/PC-1D-basin modelling software (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 as 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 western part of the study area. A "low-coalification zone" showing stagnating/decreasing coalification with increasing stratigraphic age exists, however, northeast of the Ennepe thrust, indicating synorogenic coalification. This anomaly is explained by early thrusting in the northern Rhenish Massif resulting 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 approximately 65 to less than 50 mW/m². Maximum burial depths for the base and top of the Namurian also decrease southwards from 7000 to 3600 m and 4600 to 1800 m, respectively, resulting in southwards-decreasing coalification of the 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 earlier onset of erosion, i.e. in the Westphalian B rather than Westphalian D or post-Westphalian.