Model sedymentacji ewaporatów cechsztyńskich na wyniesieniu Łeby

Abstract

MODEL OF SEDIMENTATION OF ZECHSTEIN EVAPORATES AT THE ŁEBA ELEVATION Summary During the Zechstein deposition in the Łeba elevation area the morphology of the sea bottom was mainly controlled by the fast sedimentation rate in the peripheral part of the sedimentary basin. The relief which was inherited after the Zechstein Limestone time was only insignificantly differentiated. The highly variable picture of thickness and facies development of the Lower Anhydrite was probably related to the accidental occurrences of the thickest accumulations of nodular anhydrites at the beginning of the Lower Anhydrite deposition. Such local shallower areas preferred the more rapid precipitation and later either they could merge to form elongated "barriers" or they remained isolated sulphate platforms, or they did not leave their impress on the subsequent evolution. The Lower Anhydrite deposition is distinctly cyclic. It is possible to distinguish 2 transgressive cycles in the entire area, and in the area of sulphate platforms and their slopes also the third incomplete cycle. The deposits of the latter formed simultaneously with the oldest halites in the basinal zones. The relief which formed during the Lower Anhydrite governed the chloride deposition and was finally leveled. Starting from that time, at the end of the Oldest Halite, the proximity of the land controlled the deposition of the younger members: coastal carbonate platform and basin systems have been developed, and the latter were subsequently filled in by sulphate deposits. During the Zechstein deposition in the Łeba elevation area the sea level significantly fluctuated not only at the boundaries of the cycles but also within the cycles Ignoring gradual, small changes which were especially well manifested during the Main Dolomite and Platy Dolomite deposition and were related to the cyclic deposition of carbonate platforms, the common feature of all Zechstein deposits was that the transgressions were slow and the regressions were very fast: this is characteristic of Phanerozoic sea level changes. Similar significant sea level fluctuations were noticed in other parts of the Zechstein basin what suggests their basinal nature, and therefore there is a potentiality for detailed correlation and more precise reconstruction of history of the Zechstein deposition.