Coalification pattern and thermal modelling of the Permo-Carboniferous Saar Basin (SW-Germany)

The Lower Saxony Basin, Germany, is one of the several sedimentary basins within the Central European Basin system. In its southwestern part, anomalously high maturity of organic matter has been observed to reach 4.5% VRr in Upper Jurassic and Lower Cretaceous sedimentary rocks in an area which coincides with a magnetic and a positive gravimetric anomaly. This anomaly was often interpreted as the consequence of a deep-seated igneous intrusion, the socalled Bramsche Massif. However, results obtained from calibrated numerical modelling are not in accordance with this scenario. Instead, a burial by approximately 4 km of now-eroded Cretaceous rocks was revealed to be the probable cause for the anomaly. Data and modelling results from six boreholes and two pseudo-wells support this view.

Section: Uncertainties In Modelling Resultsmentioning

confidence: 99%

Section: Coalification Patternmentioning

confidence: 99%

Numerical modelling of burial and temperature history as an approach for an alternative interpretation of the Bramsche anomaly, Lower Saxony Basin

Senglaub

Littke

Brix

2005

“…Most of this work was based on the numerical simulation studies using vitrinite reflectance data collected from individual wells (Littke et al 1994;Bu¨ker et al 1996;Hertle and Littke et al 2000) or pseudo-wells constructed from outcrop information (Oncken 1991;Karg 1998;Nö th et al 2001, see explanation of concept therein). Some of the investigations included 2D modelling (Bu¨ker et al 1996;Karg 1998).…”

Section: Introductionmentioning

confidence: 99%

Late- and post-Variscan cooling and exhumation history of the northern Rhenish massif and the southern Ruhr Basin: new constraints from fission-track analysis

Karg

Carter

Brix

et al. 2005

Apatite fission-track analyses were carried out on outcrop and core samples from the Rhenish massif and the Carboniferous Ruhr Basin/Germany in order to study the late-and post-Variscan thermal and exhumation history. Apatite fission-track ages range from 291±15 Ma (lower Permian) to 136±7 Ma (lower Cretaceous) and mean track lengths vary between 11.6 lm and 13.9 lm, mostly displaying unimodal distributions with narrow standard deviations. All apatite fission-track ages are younger than the corresponding sample stratigraphic age, indicating substantial postdepositional annealing of the apatite fission-tracks. This agrees with results from maturity modelling, which indicates 3500-7000 m eroded Devonian and Carboniferous sedimentary cover. Numerical modelling of apatite fission-track data predicts onset of exhumation and cooling not earlier than 320 Ma in the Rhenish massif and 300 Ma in the Ruhr Basin, generally followed by late Carboniferous-Triassic cooling to below 50-60°C. Rapid late Variscan cooling was followed by moderate Mesozoic cooling rates of 0.1-0.2°C/Ma, converting into denudation rates of <1 mm/a (assuming a stable geothermal gradient of 30°C/km). Modelling results also give evidence for some late Triassic and early Jurassic heating and/or burial, which is supported by sedimentary rocks of the same age preserved at the rim of the lower Rhine Basin and in the subsurface of the Central and Northern Ruhr Basin. Cenozoic exhumation and cooling of the Rhenish massif is interpreted as an isostatic response to former erosion and major base-level fall caused by the subsidence in the lower Rhine Basin.

“…The distribution of coalification grade, measured by the random vitrinite reflectance (%Rr), enables construction of surface maps and cross sections that incorporate isoreflectance lines (e.g. Kalkreuth et al 1989;Hertle and Littke 2000). The geometric relationship between isoreflectance lines and bedding planes allows differentiation between pre-, syn-and post-tectonic coalification at a regional scale (Teichmüller and Teichmüller 1966).…”

Section: Introductionmentioning

confidence: 99%

Coalification history of the Stephanian Ciñera-Matallana pull-apart basin, NW Spain: Combining anisotropy of vitrinite reflectance and thermal modelling

Frings

Lutz

Wall

et al. 2004

The Stephanian Ciaeera-Matallana Basin of NW Spain comprises 1,500 m of alluvial to lacustrine coalbearing sediments, which were deposited in a late Variscan transtensional/transpressional pull-apart setting. The relationship between coalification pattern and rock deformation was evaluated by measurements of the anisotropy of vitrinite reflectance (AVR). The AVR ellipsoids reveal both pre-tectonic elements related to the bedding fabric and syn-tectonic elements related to folding, producing biaxial ellipsoid shapes with the maximum reflectance parallel to fold axes. The mean coalification gradient for the Stephanian succession is about 0.62 %Rr/km. Calculations of the mean palaeogeothermal gradient are presented on the basis of three different empirical equations. A palaeo-geothermal gradient of 85 C/km is considered the most realistic, with an overburden of about 1,000 m. 1-D numerical modelling of the burial history results in two possible scenarios, the most preferable involving a palaeo-heat flow of 150 mW/ m 2 and an overburden of ca. 1,050 m. These results indicate that maximum coalification was related to a localised but high palaeo-heat flow/-geothermal gradient. The anisotropy of vitrinite reflectance highlights the interactive and transitional nature of sedimentary compaction and rock deformation on the maturation of organic material within strike-slip fault zones.