Thermal Maturity Of The Swiss Molasse Basin - Indications For Paleogeothermal Anomalies

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Journal Article: Thermal Maturity Of The Swiss Molasse Basin - Indications For Paleogeothermal Anomalies

Abstract
136 coal samples from outcrops of the Plateau Molasse and Subalpine Molasse of Switzerland have been collected in order to determine their maturation level and to reconstruct the thermal history during the Cenozoic. Measured mean random vitrinite reflectance values (Rr) range from 0.21 % to 0.97 %. Mean average values increase with age, from 0.39% Rr for samples from the middle Miocene OSM to 0.53 % Rr for samples from the upper Oligocene USM, situated in the Plateau Molasse. Isoreflectance lines show a general increase in thermal maturity towards the Alpine front. Pronounced variations are found in the maturity values of the Plateau Molasse. Isoreflectance contours indicate that variations in thermal maturity might have a structural control. Areas of increased vitrinite reflectance occur near fault zones or lie parallel to a major topographic structure (Lake Zurich) which may be tectonically controlled. Thermal modelling of outcrop samples in the Plateau Molasse requires maximum paleotemperatures of about 40, 70, 90 and 110-degrees-C for measured vitrinite reflectance values of 0.3, 0.4, 0.5 and 0.6 % respectively. These temperatures could have occurred in a hypothermal peripheral foreland basin, if eroded overburden thicknesses of up to 4 km are assumed. However, there is no geological evidence for this amount of burial and consecutive uplift/erosion during the Neogene, especially in the distal parts of the Molasse basin. Thermal modelling, taking into account convective heat transport, could explain in part the inferred paleotemperatures and the observed coalification patterns. Zones of increased thermal maturation may, therefore, be related to an increased regional discharge of warm groundwater controlled by tectonic structures.

Author 
R. Schegg








Published Journal 
Eclogae Geologicae Helvetiae, 1992





DOI 
Not Provided
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Citation

R. Schegg. 1992. Thermal Maturity Of The Swiss Molasse Basin - Indications For Paleogeothermal Anomalies. Eclogae Geologicae Helvetiae. (!) .