New stratigraphic scheme for Zechstein rocks in the Pogorzela High (Foresudetic Monocline) and its significance for hydrocarbon exploration

Abstract

A b s t r a c t . Results of an analysis of new 3D seismic data, obtained from the part of the Wolsztyn High in the Pogorzela High area (SW Poland), allow to test the existing knowledge regarding the geologic framework of the Zechstein rocks in this area. A characteristic arrangement of seismic reflectors within pinched-out Zechstein deposits on slopes of the high shows that they are overlapped in relation to the distinct surface of angular unconformity related to the base of the Zechstein—the Z1’seismic boundary. 3D seismic data seems to show that PZ1 strata are absent in the close vicinity of the Pogorzela High with the lower part of the PZ2 cyclothem also absent across the crest. This suggests that the interpretation of the stratigraphy of Zechstein deposits in the Pogorzela–1 and Pogorzela–2 wells (located on the crest of the high) is, in the light of 3D seismic data, questionable. Probably, the initial stages of the Zechstein transgression did not reach the most elevated part of the high, so that the Carboniferous basement is directly overlain by rocks of the Main Dolomite (Ca2), not by the Zechstein Limestone (Ca1) as was previously thought. The lack of Ca1 strata across the crest of the Pogorzela High opens new exploration perspectives in this interval and explains the apparent negative results of boreholes drilled in 1970s. Presumably it also explains differences in formation of these rocks in comparison with the central and western part of the Wolsztyn High (the Kościan–Nowy Tomyśl area).