Litostratygrafia pstrego piaskowca na Pomorzu Zachodnim

Abstract

 Omówiono litostratygrafię pstrego piaskowca na Pomorzu Zachodnim. Zaproponowano nadać rangę jednostek formalnych czterem formacjom oraz wydzielonym w ich obrębie sześciu ogniwom, które scharakteryzowano w myśl Zasad polskiej klasyfikacji, terminologii i nomenklatury stratygraficznej (1975). Przedstawiono położenie ustanawianych jednostek w profilu całego pstrego piaskowca Pomorza Zachodniego. LITHOSTRATIGRAPHY OF THE BUNTSANDSTEIN IN THE WES'TERN POMERANIA The lithostratigraphy of the Buntsandstein in the western Pomerania is discussed. Four new formations are proposed (Table 1) with reference to the existing informal subdivision. A part of the section is recognized as closely matching definition of the Baltic Formation (A. Szyperko-Śliwczyńska, l980), previously established in area of the Peri-Baltic Syneclize. The proposed formations are characterized in accordance with requirements of "The principles of Polish stratigraphic classification and nomenclature" (1975). The position of the proposed units in Buntsandstein section and the nature of boundaries between individual formations are schematically outlined (Fig. 11). A clearly diachroneous nature of boundary of the Pomerania and Połczyn Formations is stressed and extent of the formations beyond their stratotype areas is outlined (Fig. 1).As stratotype of the  R e w a l  F o r m a t i o n  is chosen a part of borehole Kamień Pomorski IG 1 at the depth of 2057.5-2024.0 m (Fig. 2). The formation comprises a series of red-brownish, unstratified, locally dolomitic claystone-mudstone rocks with numerous concentrations of anhydrite (Fig. 3).The variability in lithology of the Rewal Formation in western Pomerania is mainly connected with differences in frequency of anhydrite concentrations and presence of intercalations of rock salt and stratified, often mudstone-sandy rocks in some sections. The maximum thickness of this formation is 60–70 m (Fig. 4).In geological section, the Rewal Formation rests on rocks of various units of the Zechstein (from Pz3 to Pz4c) and it is overlain by those of the Baltic Formation of the Lower Triassic age. There is no paleontological evidence for dating the Rewal Formation and it is assumed here that it represents equivalents of various parts of the Zechstein.As stratotype of the  P o m e r a n i a  F o r m a t i o n  is chosen a part of borehole column Kołobrzeg IG I at the depth of 1931.0–1733.0 m (Fig. 6) and hypostratotype - a part of borehole columnPołczyn IG 1 at the depth of 2673.1–2320.0 m (Fig. 7).The formation is represented by a part of the section comprising two similar cyclothems. Lower parts of the cyclothems are built of pink to brick-red, calcareous oolitic-sandstone rocks, and the upper – various-coloured calcareous mudstone-claystone rocks, often displaying parallel bedding and streaks, lenses and intercalations of carbonate rocks (Figs 6–8). Lower part of the lower cyclothem is differentiated as Drawsko Sandstone Member, with a part of borehole column Kołobrzeg IG 1 at the depth of 1931.0–1893.0 m as the stratotype, and the whole upper cyclothem – as the Trzebiatów Member, with a part of the same borehole column at the depth of 1778.0–1733.0 m as the stratotype.The variability in lithology of the Pomerania Formation is connected with increase in share of sandstone rocks in north-eastern part of the studied area. The changes in thickness ratio of the Trzebiatów Member to that of the whole formation are also significant. The thickness of that member is varying from about 100 m close to the limits of its extent to about 350 m in the Mid-Polish Depression.The Pomerania Formation is correlable with lower part of the Middle Buntsandstein in the Fore-Sudetic area, Lidzbark Formation in NE Poland and the Volpriehausen Folge in Meclemburgia.However, there is still no paleontological evidence for direct dating of the Pomerania Formation. The  P o ł c z y n  F o r m a t i o n is defined by a set of stratotypes representing its sections in the borehole columns Kołobrzeg IG 1 (interval 1733.0–1448.5 m) and Połczyn IG 1 (interval 2320.0–1895.8 m).The Połczyn Formation comprises a series of brick-red and red-pinky sandstones with subordinate intercalations of mudstone-claystone rocks. The intercalations are fairly common in some parts of the section. The lowermost part of section of this formation, with some features typical of the underlayingPomerania Formation, is differentiated as the Kołobrzeg Member in part of the studied area. The stratotype of that member is a part of the borehole column Kołobrzeg IG 1 (interval 1733.0–1703.5 m). The uppermost part of the Połczyn Formation, traceable as a separate cyclothem in inner zone of the Mid-Polish Depression, is differentiated as the Świdwin Member, with a part of the borehole column Połczyn IG 1 (interval 1985.0–1895.8 m) as its stratotype.The variability in lithology of the Połczyn Formation is connected with changes in quantitative ratio of sandstones and claystone-mudstone rocks. The share of sandstones decreases southwards. The concept of the Połczyn Formation is introduced for sections with share of sandstones equal at least one-third (Fig. 10). The thickness of the Połczyn Formation rises from about 200 m at NE limit of its distribution to about 500 m in the Mid-Polish Depression.The Połczyn Formation is correlable with the uppermost parts of the Middle Buntsandstein in the Polish and German Lowlands. It presumably corresponds to the Detfurth and Hardegsen Folge and at least a part of the Soiling Folge. There is no paleontological evidence for direct dating the formation.As stratotype of the  B a r w i c e  F o r m a t i o n  is chosen the section (depth interval 1895.0–1744.3 m) in borehole Połczyn IG 1 (Figs 12, 13).The formation represents uppermost part of the Buntsandstein, with 80–90% share of clastic rocks, usually calcareous and various-coloured, and with intercalations of usually gray carbonate rocks and nodule-like concentrations of anhydrite. Its section is highly varying in the vertical and two characteristic lithological complexes may be traced throughout the area of its distribution. A member rank is here proposed for the complexes (Figs 12, 13). Lower complex, differentiated as the Czaplinek Claystone Member, is represented by gray and dark-gray claystones and clay-shales with intercalations of carbonate rocks and concentrations of anhydrite. A stratotype of that member is a part of borehole column Połczyn IG 1 from the depth of 1882.0–1856.5 m. As stratotype of the upper complex, named the Siecino Member, is chosen a series of calcareous claystone-mudstone rocks with intercalations of usually knobby limestones, recorded at the depth of 1771.5–1744.3 m in the borehole column Połczyn IG 1.The variability in lithology of the Barwice Formation is mainly connected with changes in quantitative ratio of mudstone-claystone and sandstone rocks. The share of the latter ranges from 10 to 50% of the section. The thickness of the formation is up to 180–190 m (Fig. 14).The Barwice Formation is corre1able with the RØt in other parts of the Polish and German Lowlands.It is dated at the upper most Scythian and, eventually, a1so lowermost Anisian on the basis of the record of microflora of the Voltziaceaesporites heteromorpha Zone.