Paleomiąższości, litofacje i paleotektonika epikontynentalnej kredy górnej w Polsce

Abstract

 Dokonano szczegółowej analizy obecnego i pierwotnego zasięgu osadów poszczególnych pięter kredy górnej, rekonstrukcji pierwotnej miąższości i facji w strefach częściowej lub całkowitej erozji epigenetycznej, analizy luk sedymentacyjnych oraz opracowano mapy litofacjalne metodą współczynników.Mapa paleotektoniczna powstała z nałożenia map paleomiąższości i facji. Analiza paleotektoniczna pozwoliła wyróżnić paleostruktury o zasięgu regionalnym i lokalnym. Głównymi elementami są wał środkowopolski o przebiegu NW – SE i przyległe do niego bruzdy: szczecińsko-mogileńsko-łódzko-nidziańska oraz pomorsko warszawsko-lubelska. PALAEOTHICKNESS, LITHOFACIES AND PALAEOTECTONICS OF THE EPICONTINENTAL UPPER CRETACEOUS IN POLAND Sedimentary-palaeotectonic evolution of Upper Cretaceous (including Upper Albian and Lower Palaeocene) is presented on palaeothickness and fades maps (Figs 1–8) and palaeotectonic map (Fig. 9). A detailed analysis of the present and primary extents of particular stage, as well as a reconstruction of primary thickness and fades in the zones of complete or partial epigenetic erosion, and an analysis of sedimentary gaps have been made. Lithological maps by the use of the quantitative method of lithological coefficients have been elaborated.The palaeotectonic map has been worked out by superposition of the particular of palaeoisopachs and fades maps. It presents the palaeostructural pattern of the Upper Cretaceous bottom at the end of the Cretaceous sedimentation. It presents also the results of thickness analysis, analysis of lithological associations and palaeotectonic regionalization.The Upper Cretaceous epicontinental basin in Poland is a part of the extensive Upper Cretaceous Middle European basin. From the facies analysis it results that the sediments of this basin represent themiddle stage of the tectonic cycle. It is expressed in the evolution of marine carbonate association (Fig. 9A) composed of subassociations. The terrigenous-marly sub-association is connected with the external part of the basin. The siliceous - marly - terrigenous sub-association developed in the more interior parts of the basin. The siliceous-calcareous association was limited to the middle part of the basin. The calcareous four sub-association was connected mainly with the eastern part of the basin. These sub-associations are arranged zonally with gradual transition from one to an other. The continental brackish litho fades occurred only in a part of the North-Sudetic Trough in Lower and Middle Santonian.On the bassis of highly differentiated distribution of primary thickness and fades one can presume that the area of the epicontinental Upper Cretaceous sedimentary basin was subject to both downwarpingand uplifting movements. These movements are marked on the whole area of the basin, most intensively however in the middle and south-western part of the basin.A zone of lower subsidence – the Mid-Polish Swell – developed in the axial zone of the Mid-Polish Furrow separated in Older Mesozic. The swell was formed gradually, particularly after the Turonian.The most intensive sedimentation took place on both sides of the Mid-Polish Swell in the Szczecin–Mogilno– Łódż–Nida Furrow and in the Pomerania–Warsaw–Lublin Furrow.Extensive areas with evidently lower subsidence occur outside the both sedimentary furrows. The other areas with high subsidence: the Opole Depression and the Bolesławiec–Kłodzko Depression occur in the extreme south-western parts of the basin. The erosive-sedimentary gaps are also connected with the uplifting movements, particularly visible within synsedimentary elevations and horsts partly connected with salt tectonics.The Mid-Polish Swell, uplifted in the Maastrichtian/Lower Palaeocene, as well as the areas located to the south-west of it, including the Sudety Mts and their foreland were then subjected to strong erosion. The areas situated to the north-east of Mid-Polish Swell were also elevated and eroded at that time. The erosive-sedimentary gap in the sequences is also visible even in the areas where the Upper Maastrichtian sediments are covered by Lower Palaeocene.