Journal of Petroleum Geology, Vol. 41(2), April 2018, pp 175-188
2D BASIN MODELLING IN THE EASTERN
VARISCAN FOLD BELT (CZECH REPUBLIC):
INFLUENCE OF THRUSTING ON PATTERNS OF
P. Jirman*, E. Geršlová
*, J. Kalvoda* and R. Melichar*
This study evaluates the geothermal history of Palaeozoic sedimentary rocks from the
easternmost part of the Variscan external zone in the NE Czech Republic. The objective
was to investigate the geothermal history of pre-Variscan Palaeozoic carbonates in the study
area, and to assess its relationship with that of the overlying Variscan ysch. In the study
area, the Palaeozoic succession occurs at the surface or is overlain by Miocene sediments
of the Carpathian Foredeep. Palaeozoic nappes and the main Variscan overthrust have been
documented in the subsurface at the deep Potštát-1borehole.
Vitrinite reectance measurements on 38 samples from the Potštát-1 well and 19 samples
from nearby surface outcrops and shallow boreholes were available. A 2D thermal model
was created using PetroMod and the thermal maturity evolution was modelled by EASY%Ro.
The thermal model was constructed based on interpretations of two NW-SE seismic proles
(lines 5/83 and 5/84) oriented perpendicular to the main Variscan thrusts. The results were
calibrated using measured vitrinite reectance and were adjusted with 1D models from three
shallow boreholes. At the Potštát-1 borehole, modelled maximum palaeo-temperatures of
the Variscan ysch (Moravice Formation) ranged from 310°C at a depth of 7.3 km (the top
of the preserved succession) to 395°C at the base of the succession, resulting in thermal
maturities of >4%R
. Peak maturation occurred prior to the end of Variscan thrusting.
Modelling suggests that the basal heat ow for these thrust units reached a maximum
value of 63 mW/m
at 325 Ma. In addition, the modelling suggests that the maturity of the
Palaeozoic carbonates was controlled by the thickness of the overlying Variscan ysch nappes.
Maximum palaeo-temperatures for the Palaeozoic carbonates ranged from 265°C at the
top of the interval (at a depth of 7.1 km) to 290°C at the base, resulting in a maturity of
3.8 to >4%R
which is within the dry gas window. The study suggests that basal heat ows
in the original (pre-thrust) Early Carboniferous sedimentary basin were slightly higher than
those in the post-thrust location for the Variscan ysch nappes. This should be taken into
account when evaluating the petroleum system in the South Moravian oil province (SW
Czech Republic) where a complete sedimentary sequence has not been preserved.
* Department of Geological Sciences, Faculty of Science,
Masaryk University, Kotlářská 2, 611 37 Brno, Czech
author for correspondence: firstname.lastname@example.org
Key words: basin modelling, vitrinite reectance, maturity
reversal, Rheno-Hercynian Zone, Variscan belt, Czech
Republic, thermal maturity, Palaeozoic.
© 2018 The Authors. Journal of Petroleum Geology © 2018 Scientic Press Ltd
Gerslova.indd 175 02/03/2018 14:41:05