Klastyczme utwory transgresywne cechsztynu wyniesienia Łeby na tIe modelu facjalnego basenu ewaporatowego

Abstract

Clastic transgressive deposits of the Zechstein in the Łeba elevation against the facial pattern of an evaporite basin

Statistical correlative connections have been determined between the thickness of the transgressive sandstones of the Weiss Liegendes (MZL) occurring in the Zechstein bottom (Upper Permian) and the thickness of the remaining lithological components of the Werra cyclothem. The necessary data have been obtained from borehole profiles situated in the eastern margin of the Łeba elevation (central part of the Polish Baltic Coast): Regression lines have been plotted showing the interdependence of the thickness of the Weiss Liegendes and the following variables: total thickness of the Werra cyclothem (MWE), thickness of the Zechstein limestone (MW), summaric thickness of anhydrites in the Werra cyclothem (MA), thickness of salts (MS) and the summaric thickness of the Werra saltless deposits (MBW). The studied interdependence and the corresponding regression lines have been diagramatically shown in Figs 1-6. This provided the basis for plotting the pattern of the primary original changes in the thickness of lithological components within the sedimentary basin of the Werra cyclothem. The sedimentation pattern shown in Fig. 8 does not comprise the rock salt while that in Fig. 9 takes account of the minimum original thickness of NaCl. The plotting of these patterns was feasible by taking advantage of the statistically existing correlations: MBW vs MZL(=T);MZL vs MA(=A); W=MW=MBW-(T+A) for the pattern in Fig. 8 and MWE v sMZL (=T);MZL vs MW(=W);MZL vs MA (=A)for that in Fig. 9 where the hypothetical salt thickness (MS) was obtained: S=MWE-(T + W + A). This resulted in the determination that relatively the strongest correlative connection exists between the thickness of the terrigenous Weiss Liegende deposits and the total thickness of the Werra cyclothem. This provides additional evidence that the Weiss Liegende sandstones are a transgressive product of the Zechstein sea and are stratigraphically referable to the Upper Permian. Their thickness increases towards the basin shores (Figs 8-9). It is reasonably supposed that they are the geochronological correspondent of the Zechstein limestones (W) while in the off-shore part of the basin they may correspond to the anhydrites (A) and, even to the rock saIts (S) -Figs 8 -9. Changes in the thickness of the Weiss Liegende are a reliable Iithofacial index making possible the reconstruction of the original quantitative relations in the peripheral parts of the evaporation basin. In this zone the carbonate rocks and the anhydrites decrease in thickness towards the basin shores while the central part of the basin (Fig. 9) is occupied by rock salt.