Wgłębna budowa geologiczna podłoża Bałtyku na wschód od ujścia Odry

Abstract

DEEP GEOLOGICAL STRUCTURE OF THE BALTIC SEA SUBSTRATUM EAST OF THE ODRA RIVER MOUTHSummaryThe results of the seismic surveys made in 1964–19165 at sea within the south-western part of the Baltic basin, between the Odra River mouth and the meridian of Koszalin (Fig. 6), are discussed. The surveys were conducted by the Soviet seismic crew using reflexion method. Good results were obtained in the Permo-Mesozoic series. The deepest horizon (marked here with a letter F) occurs within the time extents up to 2,2 sec. It is thought to belong to the Zechstein.Lack of any complex elaboration of mean velocities on land and at sea has forced to analyse mainly time cross sections ·and time maps. Depth interpretation (Figs. 2­–5) can be charged with a great error, mainly in synclines.The main structural units ascertained on land (Figs. 1 and 6) continue in the Baltic sea area. Dislocation zone of Koszalin is thought to be related to the south-western faults of Bornholm, that of Trzebiatów – to the faults bounding from SW the external Pre-Cambrian horsts of Scania.Dislocation zone of Kamień prolongs in turn towards NNW and does not seem to be related to the faults of northern Rügen (Fig. 6).The area reveals here a deep block structure conditioned by the fault-flexural zoes mentioned above (Figs. 3, 4. and 6 – blocks of Darłowo, Kołobrzeg, Gryfice and Wolin – I–IV). The blocks sink in a step-like manner towards SW, the block of Kołobrzeg showing in the north a strong relation with the platform area of the block of Darłowo (Fig. 7). Vertical movements of these blocks were responsible for the changes in thickness of the Permo-Mesozoic series and the tectonic deformations of this series. As a result of this, some anticlinal forms of swell and placanticline types were produced (Figs. 1 and 2). The Mesozoic anticline of Kamień – a north-western branch of the Pomeranian swell – bears no relation to the Grimmen swell of the north-western area of Germany. After the Upper Cretaceous time, the main fault-flexural zones discussed above were rejuvenated, although in the previous periods they must have played a considerable role, as well. This f. ex. is proved by the facial relations existing in the Zechstein on either side of the Koszalin zone, as well as by a contact of the younger and older Palaeozoic along this zone, and the estimated contact of the Lower Permian with the Devonian and Carboniferous along the Trzebiatów zone. The problem of the relations between the northern Rügen, and the region of Koszalin has not so far been explained. In both areas, graptolite schists of Ordovician age (hypothetical Caledonian ridge), strongly displaced tectonically, were encountered by drillings.An almost west-easterly trend of some fault zones that separate the northern part of the block of Kołobrzeg, can be regarded here as the only trace of these relations. The problem of connections between the Zechstein basins of northern Denmark and of west Pomerania is not cleared up, at present It appears, however, that these were separated by a hump running in a west-east direction along the line Arkona-Darłowo. As a rule, the Triassic and Jurassic series thin out towards the north, and, in this direction, the Cretaceous deposits probably rest on older and older Jurassic members. The Cretaceous series thicken towards the north to reach, west of the Trzebiatów fault, their maximum thickness, amounting here to 1500 metres.