Dolny trias na Pomorzu Zachodnim

Abstract

LOWER TRIASSIC IN THE WEST POMERANIA AREA

Summary

In the area of West Pomerania are found all members of the Lower Triassic, i.e. Lower and Middle Buntsandstein and Roethian. The Lower Buntsandstein reaches its maximum thickness in the area of the bore hole Świdwin 2, where it amounts to about 800 m. Two series may be distinguished in the Lower Buntsandstein: lower series and upper series. The lower series constitutes a lithologically monotonous complex characterized in the whole area by a uniform thickness from 330 to 430 metres. The complex consists of the alternating calcareous claystones and mudstones, red-brown with green spots. They are characterized by the presence of various laminae, lenses, interbeddings and intercalations of marly and mudstone limestones, and by the occurrence of anhydrite aggregations. The lower part of this series is built up of rocks characterized by dolomitization. These may probably be referred to the Zechstein. The upper series of the Lower Buntsandstein reveals an irregular thickness in the area considered. The thickness ranges from 175 m at Kamień Pomorski to 400 m at Świdwin 2. Two sectors may be distinguished in this series; each of them contains an oolitic-arenaceous complex at the base, easily traceable on the diagrams of geophysical measurements. At the top, in turn, the sectors reveal a complex of calcareous, clay-mudstone rocks with intercalations of mudstone limestones and sporadically of arenaceous limetstones, also with anhydrite aggregations. The rocks occurring in the upper series are red-brown, violet, locally greenish in colour; frequently they show some traces of drying up, hieroglyphs and ripple marks. The Middle Buntsandstein reaches its maximum thickness in the area of the bore holes Połczyn and Świdwin, amounting here approximately to 400 metres. Here are found sandstones, mudstones and calcareous claystones, brick-red in colour, sometimes light grey, grey and green. On the sandstones there occur clay balls forming at places a kind of conglomerate layers. In the upper most part of the series, in mudstons and claystones, there are, found not numerous aggregations of anhydrite. Roethian in the area considered is characterized by uniform thickness from 150 to 170 metres. Here, three members can be distinguished, determined in this paper as Roethian A, Roethian B and Roethian C. At the base of the Roethian A are commonly found grey-green, diagonally bedded sandstones with intercalations of mudstones and claystones. These are overlain by a very characteristic complex of grey claystones and clay shales with laminae of mudstones, intercalations of dolomite and numerous aggregations of anhydrite. The uppermost portion is built up of brown claystones and mudstones with aggregations of anhydrite and not numerous intercalations of dolomite and sandstone. Here, a characteristic zone occurs revealing traces of feeding ground of worms. Roethian B represents a complex of typical clastic character. It consists of sandstones, mudstones and claystones, calcareous at places, and off various colour. Frequently, the sandstones contain clay-mudstone balls and intercalations of conglomerates made of these latter. Anhydrite aggregations are here rarely found. Roethian C consists of intertonguing nodular marly limnestones and of marly claystones and mudstones. In the lower part there occur also marly sandstones. In the deposits mentioned above imprints of lamellibranches and individual lingulae are not numerous. A connection of the above stratigraphical scheme with those of the Lower Triassic occurring in other areas is, as far as the Lower and Middle Buntsandstein is concerned, relatively simple. However, such a connection of the discussed subdivision of the Roethian with the detailed stratigraphical scheme of the Roethian of other areas appears at present to be impossible.