The pre-Permian of NW-Germany – structure and coalification map

摘要

A new structure and coalification map of the pre-Permian subcrop in NW-Germany is presented. In addition to presenting the coalification pattern, it is the aim of the map to illustrate the structural evolution of the northern Variscan fold belt and foreland in NW-Germany. During the Carboniferous the tectonic evolution was strongly influenced, respectively by the foreland of the Variscan orogen in the South and the Central European Shear Zone bordering the East European platform in the North. Generally, two types of basins developed in front of the prograding Variscan orogen: (1) Close to the orogen flexural basins, the Aachen and Ruhr basins were formed as a response to the load of the orogen, (2) further north, in the outer foreland, wrench induced basins, such as the Lower Saxony Basin, developed. The Variscan Deformation Front (VDF) was formed during the Stephanian. South of the pre-Variscan Brabant Massif and extending into the Aachen Basin, the Variscan Deformation Front is narrow and thrust dominated. In the Ruhr Basin to the East, a fold belt developed with upright folds and spreading far to the NW. The VDF is abruptly terminated in the North-east by the Osning Transfer Fault Zone, where it is offset some 100 km towards the Southeast. Within the Lower Saxony Basin and the Pompeckj Block, no Variscan orogenic folding has been observed. This foreland area was subjected to transpressional and transtensional wrench-type deformation along the WNW—ESE and SSW—NNE trending faults of the Central European Shear Zone. Post-Variscan reactivation of the shear zone initiated and controlled the sedimentary infill of the currently named Northwest German Basin. The different structural evolution south and north of the Variscan Deformation Front is reflected by the coalification pat-tern. Within the Variscan Fold Belt the pre- and synorogenic (Asturian) coalification caused SW—NE orientated iso-reflectance lines. In contrast, in the northern foreland the Variscan coalification and the subsequent Mesozoic and Cenozoic coalification formed a WNW-ESW orientated coalification pattern. A revision of the coalification pattern of the Lower Saxony Basin revealed that the iso-reflectance lines run parallel to the margins of the basin suggesting a close relationship between the wrench dominated basin tectonics and coalification. Models of basin burial history provide strong evidence that maturation in the Lower Saxony Basin is mainly related to deep burial during the Late Cretaceous, followed by uplift and erosion and not by igneous intrusions.