Absenkungs-, Erosions- und Wärmeflußgeschichte des Ruhr-Beckens und des nordöstlichen Rechtsrheinischen Schiefergebirges

The burial and thermal his tory of Palaeozoic and Mesozoic strata in the Münsterland and Ruhr basin and the northem part of the Rhenish Massif east of the river Rhine was reconstructed applying 1D- and new 2D-forward modelling. The basin evolution model was calibrated using vitrinite reflectance and fluid inc1usion data, and results of apatite fission track analysis and Rock-Eval pyrolysis. The 1D-simulation of more than 40 wells and pseudo-wells from the study area led to an understanding of the basin evolution. A 2D-simulation was performed for the northern, 90 kilometre long part of the seismic line DEKORP 2-N which crosses the eastern part of the Münsterland and Ruhr basin and the northern part of the Rhenish Massif east of the river Rhine. Apatite fission track analyses gave c1ear evidence that the coalification of the Palaeozoic rocks occured at the time of maximum burial and prior to uplift during latest Carboniferous and/or early Rotliegend time. Hence, modelling their thermal maturity applying the kinetic EASY%Ro approach yielded the following results: • The amount of Carboniferous sediment eroded increased southward, from a thickness of about 2000 m in the northern Ruhr basin to about 6500 m in the southern part of the study area (Attendorn-Elspe sync1ine). Whether the overlying sediments in the eastern Ruhr basin and the northern Rhenish Massif were entirely eroded during the late Carboniferous and/or early Rotliegend phase of basin inversion or partly at later times remains uncertain. If they were entirely eroded - likewise in the western Ruhr basin - the reconstructed amount of eroded overburden would quantify the uplift of the study area during the late Variscan orogenie phase. • A schematic stratigraphie c1assification of the eroded overburden suggests - in contrast to previous reconstructions of the palaeogeographic situation during the late Carboniferous - that sedimentation reaehed far to the south and that Stephanian sediments were deposited in the area of the present-day Ruhr basin. Westphalian sediments must have been present even in the Rhenish Massif, where they are now completely absent. • Significant uplift caused by the Variscan orogeny did not affect the study area before the latest Carboniferous (Stephanian), although there are some indications of initial tectonic activity already in the Namurian and Westphalian. • The crustal heat flow in the latest Carboniferous was significantly lower than that reported in former studies. Only for the northernmost part of the study area were elevated heat flows, up to 75 mW/m$^{2}$ (mW = milliwatts), indicated. Southward, heat flows rapidly decreased, down to values close to the continental average (about 60 mW/m$^{2}$), corresponding well with the assumed palaeotectonic setting of the study area. The regional difference in basal heat flow may best be explained by an orogenie thickening of the crust in the southern part of the study area or with a rift related thinning of the crust north of the study area in Stephanian/Autunian times. However, the unknown thermal properties of the eroded overburden causesome uncertainties with respect to the regional heat flow pattern. The following information on the Mesozoie and Cenozoic evolution of the study area was derived from apatite fission track analyses: • The entire study area was reburied during the late Permian, Triassie and early Jurassic. At times of maximum burial, the present-day Palaeozoic surface was overlain in the Ruhr basin by at least 1700 m and in the Rhenish Massif by at least 1200 m of strata. • The Ruhr basin was again an area of sedimentation in late Cretaceous and early Tertiary times. The present day Cretaceous surface was overlain by at least 600 m of strata. • The Ruhr basin was inverted in the late Jurassic and early Cretaecous and again after the Cretaceous and early Tertiary reburial in the late Tertiary, causing the erosion of the above mentioned additional overburden. • The Rhenish Massif was gradually uplifted throughout the Mesozoic and Cenozoic with an increased rate of inversion in the late Tertiary. No late Cretaceous reburial was indicated by the fission track data for this region. - 1D-simulations of wells in surrounding the study area revealed no justification for assuming elevated heat flows in the areas of the Lippstadt and Krefeld highs and in the Ibbenbüren area. The coalification pattern in these regions most likely was caused by a deep burial of the strata and moderate heat flows