Analiza paleotektoniczna i rozwój utworów saksonu w środkowej części monokliny przedsudeckiej

Abstract

PALEOTECTONIC ANALYSIS AND DEVELOPMENT OF THE SAXONIAN IN CENTRAL PART OF THE FORE-SUDETIC MONOCLINE Summary The knowledge of history of Early Permian Basin of central and western Europe will remain unsatisfactory until uniform subdivision of the section into small, equal- time correlative • intervals is worked out and its paleogeography reconstructed. The identification of three major sedimentary cycles in the central basin and minor ones in Poland has already resulted in some progress, making it possible to propose more accurate lithostratigraphic subdivision of the Saxonian in the Central European Permian Basin. Paleogeographic reconstructions of individual. parts of the vast basin should give the basis for working out a model of spatial development of the whole basin as well as a lithofacies model. After major Saalian movements, in the area of Poland the sedimentation. was mainly taking place in completely isolated lakes, supplied by seasonal rivers. Along with time, extent of lakes began to grow and the lakes merged with one another to form large basins. When Polish Late Saxonian basins, northern and southern; became connected with the central one, sea could enter area in the east. The analysis of these changes in area of Poland showed that the Zechstein represents a continuation of Saxonian in the Central European Basin and that the Saalian riftogenesis marks the beginning of post-orogenic stage in development of the Variscan platform. The borehole record of the Saxonian appears fairly good in areas of the Variscan platform. With a help of paleotectonic analysis this made possible identification of some desert lithofacies (eolian, fluvial, and lacustrine) as they were developing in a definite morphological setting and facies succession. However, reconstruction of a complete facies model still appears possible for some parts of the southern Poland basin only. This is the case of the Late Saxonian river system and dune fields from southern paleoslope of the Wolsztyn Upland, and adjacent flood plain, for which such reconstruction has been made. On the basis of the hitherto obtained results of paleotectonic analysis the following facies model may be proposed for Saxonian strata in the southern Poland basin. At the end of the Saxonian, geomorphological relations were still highly diversified in that area, characterized by extensive pediments gently sloping down from elevations in the south and north. The pediments, covered with coarse clastics, were cut by seasonal river valleys. In the lowermost, outwards drained part of the basin there existed some playa, surrounded by some sandy dunes. In the light of data on the Saxonian paleogeography, subdivision of shallow part of the Fore-Sudetic Monocline into eastern, central, and western parts appears justified. Even more justified is subdivision of that area in to northern and southern parts with reference to the course of the Wolsztyn Island Paleoelevation. In Poland, the Rotliegendes has been subdivided into Lower and Upper and, subsequently, into cycles, which made it possible to state that initial stages of development of this intracontinental basin are explainable with the use of the known geographic cycle of W. Davis. This closed basin has originated in result of two denudational cycles, Asturian. and Saxonian, in time interval of about 40 Ma. Thus, two stages (Saxonian and Zechstein) may be identified in development of an epiconitinental transgression in the Central-European Basin. In the earlier, Saxonian stage, the transgression affected the present North Sea and northern Germany, i.e. areas connected by shallow Norwegian Strait seaways with open sea. Marine ingressions coming this was started to reach central parts of the basin in the Late Rotliegendes, extending as far eastwards as Mecklenburgia, Brandenburgia and Lower Saxony. The Zechstein stage corresponds to a further increase in extent of the basin in areas of northern and central Poland.