Sedymentacja utworów cechsztyńskich wapienia podstawowego w rejonie Wrocławia
Abstract
SEDIMENTATION OF THE ZECHSTEIN BASAL LIMESTONE IN THE WROCŁAW REGION
Summary
The development and history of sedimentation of the Basal Limestone in peripheral parts of the Zechstein basin are discussed. In the south, the Basal Limestone section is increased in thickness and bipartite: its lower part comprises strongly sandy oncolites, separated from the overlaying biomicritic parts by a 1-2 cm thick layer of black shale or strongly clayey micrites. In the north, the top of the Weissliegendes is locally overlain by Basal Limestone layer usually represented by sandy micrites with bioclasts and less than 10 cm in thickness. The carbonates originated in aerobic shallow sublittoral environment, and shaly sediments - under an anaerobic (regularly laminated black shales) and dysaerobic (bioturbated shales) conditions, below storm wave base.
Correlations and environmental interpretation of microsequences of the Basal Limestone and Kupferschiefer show that lower part of the Basal Limestone from the southern region, similarly as the w hole Basal Limestone from the north, represents a continuation of clastic Weissliegendes sedimentation from early stage of stabilization of marine conditions. Taking this into account the sediments may be treated as a carbonate variety of the Weissliegendes ones.
The interfinging of shaly and carbonate sediments of the Basal Limestone may be interpreted as a net result of paleorelief differentiation, stratification in this shallow basin, and temporary changes in position of chemocline. The changes were presumably due to glacieustatic oscillations of sea level. Chronohorizons established at the basis of these changes suggest a possibility to redefine lower boundary of the Basal Limestone (Fig. 5).
Summary
The development and history of sedimentation of the Basal Limestone in peripheral parts of the Zechstein basin are discussed. In the south, the Basal Limestone section is increased in thickness and bipartite: its lower part comprises strongly sandy oncolites, separated from the overlaying biomicritic parts by a 1-2 cm thick layer of black shale or strongly clayey micrites. In the north, the top of the Weissliegendes is locally overlain by Basal Limestone layer usually represented by sandy micrites with bioclasts and less than 10 cm in thickness. The carbonates originated in aerobic shallow sublittoral environment, and shaly sediments - under an anaerobic (regularly laminated black shales) and dysaerobic (bioturbated shales) conditions, below storm wave base.
Correlations and environmental interpretation of microsequences of the Basal Limestone and Kupferschiefer show that lower part of the Basal Limestone from the southern region, similarly as the w hole Basal Limestone from the north, represents a continuation of clastic Weissliegendes sedimentation from early stage of stabilization of marine conditions. Taking this into account the sediments may be treated as a carbonate variety of the Weissliegendes ones.
The interfinging of shaly and carbonate sediments of the Basal Limestone may be interpreted as a net result of paleorelief differentiation, stratification in this shallow basin, and temporary changes in position of chemocline. The changes were presumably due to glacieustatic oscillations of sea level. Chronohorizons established at the basis of these changes suggest a possibility to redefine lower boundary of the Basal Limestone (Fig. 5).