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1 2006

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Upper Jurassic carbonate buildups in the Carpathian foreland in Poland: geological and geophysical setting

Jędrzejowska-Tyczkowska H., Golonka J., Misiarz P., Krobicki M., Matyszkiewicz J., Olszewska B., Przejczowska A., Oszczypko N.

Volumina Jurassica

2006

Vol. 4, no. 1

92-93

The Upper Jurassic carbonate sediments in the Carpathian foreland in Poland are exposed in the Polish Jura Chain and covered by the Outer Carpathian thrust and Neogene sediments of the Carpathian Foredeep. The thickness of marine Jurassic-Cretaceous carbonate series exceeds 1000 m in southern Poland and Ukraine covering the North European Platform. The lithology of the Upper Jurassic and Lower Cretaceous deposits reflects the main stages of sedimentation on the European Platform caused by eustatic changes of sea-level as well as local tectonics. Two megasequences could be distinguished here (Golonka & Kiessling 2002). Lower Zuni II, began with the Middle Jurassic transgression and ended with Early Tithonian regression. Lower Zuni III lasted from Early Tithonian to the general Early Valanginian regression. There is a gap between Lower and Upper Cretaceous deposits in the whole Carpathian Foredeep area. The Lower Zuni II starts with sandstone-gaize series passing upward to the Callovian nodular limestones covered by Lower Oxfordian calcareous sponge deposits (Golonka 1978; Olszewska 2001). The carbonate buildups of thickness from few dozens to few hundreds meters are common within the calcareous sponge series. They form hills in the Polish Jura Chain between Kraków and Częstochowa (Matyszkiewicz 1997), in the SW margin of the Holy Cross Mountains and have been recognized in the numerous 2-D and 3-D seismic subcrop sections. Interpretation of the 3D seismic data in the central part of the Carpathian foreland resulted in the recognition of several large Lower Oxfordian biohermal buildups exceeding 1 km in diameter (Misiarz 2004). Comparison with the outcrop data and seismic velocity models allows to propose new facies architecture model. The large bodies seen on the 2D seismic lines represent the clusters of small buildups. Similar clusters exist in the Jurassic outcrops in the Polish Jura Chain in the Ogrodzieniec and Olsztyn areas. The Ogrodzieniec hill was a subject of the syntethic seismic modeling of the outcrop. The impedance was calculated from the petrophysical studies of rock samples. Impedance inversion velocities were used to construct simple velocity model of a selected biohermal object and a synthetic seismic profile. Explaining internal heterogeneity of bioherms is crucial for treating them not as a single prospect but as a complex of drilling targets.