Rozwój paleozoiku w obniżeniu podlaskim

Abstract

DEVELOPMENT OF PALAEOZOIC IN THE PODLASIE DEPRESSIONSummaryAn interest in the Palaeazoic formations in the Podlasie depression was taken in 1958 after the discovery of crude oil shows in bore hole Żebrak and of natural gas manifestations in bore hole Tłuszcz in 1962 (Fig. l). Crude oil and gas occurrence in the Cambrian and Ordovician deposits in ths area was proved by next drillings made by the Geological Institute and Petroleum·Industry. The research is carried on by means of drillings made down to a depth of 4500 m. In the Podlasie depression the crystalline basement makes for the most part the bottom of the Palaeozoic, and only in the eastern region, within the border zone – the Cambrian is underlain with the Eocambrian formations that rest on the basement (Fig. 3). The Cambrian begins here with the clay-arenaceous deposits with scarce non-trilobite fauna (Coniconchia) that evidences the Sub-Holmia zone. It has been ascertained that the Sub-Holmia Cambrian formations rest directly on the crystalline basement (Fig. 4). The Cambriain sedimentation terminates in the Podlasie depression with the Middle Cambrian (Fig. 5 ). Tremadocian deposits occurs within the Białystok area only (Fig. 6), whereas the Arenigian transgression, encroaching from west, covers the whole area of the depression, similarly as the remaining members of the older Palaeozoic with same local oscillations (Fig. l3). Facial changes run perpendicularly to the general line of the marginal zone of the platform thus proving that the elevations situated north and south of the Podlasie depression were formed in a later period and did not influence decisively the sedimentation of the older Palaeozoic. Devonian deposits are absent in the·Podlasie depression. Carboniferous is represented only by the continental – marine deposits of Visean and Namurian age barely in the southern part of the depression. Zechstein makes a bay in which three distinct sedimentary cycles developed: Zl, Z2 and Z3.Due to the movements of the platform margin, main dislocations of a NW-SE direction were produced before the Paleozoic time. Only at the close of the Devonian period a different tectonic activity developed, resulting in the formation of horsts and elevations, as well as of grabens and throughs. At the Permian time a deep Zechstein bay invaded the gradually lowering area. As a result of this the Zechetein Podlasie depression developed on too basis of the previous Podlasie basin and then was obliterated during the Mesozoic processes.