Cechsztyn w zachodniej części polskiego akwenu Bałtyku

Abstract

W zachodniej części polskiego akwenu Bałtyku występują wszystkie cztery cyklotemy cechsztynu, przy czym najmłodszy z nich PZ4 ma zasięg ograniczony do południowej części akwenu. Rozprzestrzenienie litofacji ewaporytowych, z solami kamiennymi włącznie, w cyklotemach PZ1 i PZ3 sięga daleko ku połnocnemu zachodowi. Stopień zróżnicowania miąższości i facji cechsztynu, podobnie jak na przylegającym lądzie, jest bardzo duży i wykazuje wyraźną strefowość. Jest to wynikiem oddziaływania na sedymentację cechsztynu ruchów tektonicznych bloków podłoża związanych z przebiegiem lineamentu Teisseyre'a-Tornquista, połnocno-zachodniej platformy prekambryjskiej oraz późnohercyńskich stref dyslokacyjnych. Zechstein in the western part of the Polish Baltic areaDrilling operations and seismic survey have allowed to general exploration of extent, facies and stratigraphy of Zechstein. The boundaries of the Zechstein Basin composing a bay here were formed by differentiated subsidence of tectonic blocks of the basement of various genesis. The north-eastern boundary run along the Koszalin Dislocation Zone (Fig. 1), forming the northern section of the Teisseyre-Tornquist Lineament (the T-T Zone). The Zechstein Basin limits the Late Hercynian Adler Fault in the west. Between these zones, over lowered tectonic blocks K and L, a wide bay extending far northwestward was formed. Zechstein perhaps is present in the Ronne Graben near Bornholm and the possibility of direct connection between the Polish Basin and Danish Basin should be consider again. Zechstein surposes trangressively various Rotliegendes formations, and beyond their extent (north-eastern part) over various stratigraphical units of Younger and Older Palaeozoic. The PZl cyclothem is developed in a faull lithostratigraphical profile (Fig. 2). It characterizes with relatively large thicknesses and high litho facial differentiation with a high fraction of evaporites, especially the oldest rock salts (Fig. 3). Along the Adler Fault there was a narrow, lowered zone of the nature of a graben that perhaps introduced Zechstein into the Ronne Graben. Considerable decreasing of marine extent took place in the PZ2 cyclothem. In Main Dolomite (Ca2) the whole block Land the northern part of block K took up a wide carbonate platform (Fig. 5), separated with the narrow Rewal Bay from the unique Kamień Platform. Variability in thickness and Main Dolomite facies is not less here than in the land area. The older rock salts with not too much thickness occur only in the southern part (Fig. 4). The PZ3 cyclothem characterizes transgressive overlap and far northwestward extent of evaporites over the block K (Fig. 6). A primary extent of this cyclothem was likely wider than of PZl. The PZ4 cyclothem evaporites belonging only the subcyclothem PZ4a occur only in the southern part. While red siltstones of the Rewal Formation (a facial homologue of evaporites PZ4) -Fig. 7 - are widely spread.A set of lithofacial zones and variability of Zechstein thickness are distinctly zonal due to a set of local and regional areas with various subsidence connected with movability of various genesis tectonic blocks of the Zechstein basement. NW - SE directions dominated in the north-eastern part according to the run of the Koszalin Dislocation Zone forming the northern part of the T-T Zone (Fig. 1). In the central part, directions change into WNW-ESE according to the Precambrian Platform edge deviated in this direction. In the central part of block K the area of decreasing Zechstein thickness shows these directions, cleary seen on the facial map PZl (Fig. 3). The area occur in extension of the Wiek Fault Zone (GDR). In the north-western part changes of the Zechstein thickness and facies were resultant between NW-SE and N-S directions. This latter direction results in the run of the Late Hercynian Adler Fault that forms the eastern boundary the land areas, connected with the Ringkobing - Fyn and Arcona Elevations. Zechstein shows high diversification in thickness and facies. Actually it may be higher than it is presented on maps.