Lias i retyk na Mazurach

Abstract

LIAS AND RHAETIC IN THE MAZURY REGION

Summary

In the Mazury Region (north-eastern area of Poland, Fig. 7), the Rhaetic formations are bipartite (Figs. 1­4). Their lower part (Nidzica Beds) is a product of erosion and of rapid redeposition of Triassic deposits. It consists of variegated, frequently conglomeratic, clay-carbonate-arenaceous deposits. These contain fauna, which points to a very short-lived infiltration of brackish-marine water. The upper part of the Rhaetic (Bartoszyce Beds) is built up of clays tones, siltstones and grey sandstones,  allowing us to correlate them with the Triletes Beds in Germany.
The Rhaetic formations discordantly overlie various Triassic members _– from Keuper in the south, to Buntsandstein in the north. The Nidzica Beds do not .occur in the northern part of the area, and the Bartoszyce Beds are not found south of the Mazury Region. As a whole, the Rhaetic is strongly reduced (Table I), its maximum thickness amounting to 71.5 m, as compared with its thickness amounting to 300-400 metres in the area of Central and West Poland.
To the north-east of the central sedimentary furrow (Kujawy Region) Liassic, too, is characterized by a considerable change in its section. In the zone situated close to the furrow, the thickness rapidly decreases (down to 300–500 metres, Fig. 6), although the section seems to be developed almost completely. At the same time, all influences of the marine basin disappear. More to the north-east, the further reduction in thickness (Fig. 6) is accompanied by some gaps that appear in the deposits considered.
Thin, siltstone-clayey deposits of the Lowermost Lias (Figs. 1–4) with Nathorstisporites hopliticus J u n g are not known to occur in the Mazury Region, being, however, found south of this area (Liwiec Beds). The lowermost member of the Lias in the Mazury Region consists of the Olsztyn Beds which are built up of sandstones of inland provenance, bearing few clay intercalations. These beds, at most 160 m in thickness, belong probably – as it is proved by palynological analysis – mainly to the Middle Lias.
These overlie the Upper Liassic deposits developed similarly as in the other regions of Poland. Here belong the Ciechocinek Beds (the lower part – up to 40 m in thickness) developed as claystones, siltstones and grey and grey-green sandstones with Estheria representatives, as well as the Borucice Beds (the upper part – up to 30 m in thickness), which consist of sands and sandstones of inland origin.
Within the north-eastern marginal parts of the area in study (Fig. 5), various Liassic beds are transgressively overlain with the uppermost Dogger formations.