Budowa geologiczna podłoża trzeciorzędu w rowach Złoczewa i Gostynia (monoklina przedsudecka)

Zbigniew Deczkowski, Irena Gajewska

Abstract


Na ukształtowanie budowy geologicznej podłoża trzeciorzędu rowu Złoczewa i Gostynia wpłynęły ruchy tektoniczne na przełomie kredy i trzeciorzędu oraz w starszym trzeciorzędzie. Z badań wynika, że początek tworzenia się rowu trzeciorzędowego Gostynia przypada na oligocen, natomiast rowu Złoczewa na miocen.

GEOLOGICAL STRUCTURE OF BASEMENT OF THE TERTIARY IN THE ZŁOCZEW AND GOSTYŃ TROUGHS (FORE-SUDETIC MONOCLINE)

Geological structure of basement of the Tertiary in the Złoczew and Gostyń troughs was studied in detail on the basis of drillings made within the frame of survey of Miocene brown coal deposits. The studies showed that the trough zones are consistent in outline with patterns of local negative gravity anomalies. Some data on deep structure of the {rough zones were also given by reflection scismic surveys which revealed a specific downwarp of individual reflectors in the Zechstein-Mesozoic complex. The Złoczew trough is situated in NE part of the Fore-Sudetic Monocline. In NE it contacts the Poznan - Kalisz regional dislocation zone, and in the south - a row of Wieluń - Widoradz uplifts (Fig. 1). The studies showed that the major outlines of the trough and adjoning Poznań - Kalisz dislocation zone and the row of Wieluń - Widoradz uplifts have been formed in result of tectonic events in the latest Cretaceous - Early Tertiary times.

Before the onset of sedimentation of the Tertiary, the Złoczew trough zone has been subjected to tension which resulted in origin of a diversified system of faults and fractures in a belt varying form several hundred m to about 2 km in width (Fig. 2). SW - NE oriented faults arc consistent with the present course of the trough and those NW - SE - with direction of break-up of basement blocks within the trough. Blocks bounded by the faults were subsequently subjected to vertical translocations ranging from some tens to several hundred meters in amplitude (Figs. 3, 4). Stratigraphic studies showed that rocks overlain by the Tertiary in individual blocks are ranging in age from the Middle and Upper Oxfordian to Lower Kimmeridgian or even Upper Cretaceous (Fig. 2).

The Gostyń trough represents an element of the Poznan - Oleśnica regional dislocation zone (Fig. 5). The studies showed that Tertiary troughs of that zone follow earlier tectonic foundations as their course is consistent with that of a series of Rhaetian-Lias troughs.

The structure of basement of the Tertiary in the Gostyń trough has been formed in result of tectonic movements dated at the latest Cretaceous -Early Tertiary. The movements resulted in rejuvenation of the Rhaetian-Lias fault system. The Tertiary rests on Lower Jurassic and Upper Rhaetian strata in basement blocks in NW part of the Gostyń trough, and older members of the Rhaetian and, locally, Upper Rhaetian in SE part (Fig. 6).


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