Rozprzestrzenienie utworów liasu we wschodnim obrzeżeniu Gór Świętokrzyskich

Abstract

OCCURRENCE OF LIAS IN THE EASTERN MARGIN OF THE ŚWIĘTOKRZYSKIE MOUNTAINS

Summary

The present work is an attempt at presenting new cartographical conception of the Lower Jurassic within the area of classical studies carried out by. J. Samsonowicz (1929, 1934).

The author makes an endeavour to distinguish cartographically, for the first time in this area (Fig. 1), the individual (9) series of the new subdivision of the Lower Jurassic. This attempt was also favourable for a more precise determination of the Liassic boundary, allowed its range to be investigated eastwards (by about 28 km). A series of so far unknown transversal and longitudinal dislocations, which cut the Liassic deposits, or separate them from the Mesozoic and Palaeozoic formations, have been traced. Due to the Quaternary sediments covering the area in study, and on account of a small amount of adequate drillings, the investigation of some elements of geological structure has been supported by the author with the results of gravimetric surveys. The Liassic deposits here considered, like the prevailing part of the Liassic series in Poland, are developed mainly in "estuarine" facies. Recently, more and more traces of more or less intense marine ingressions have been observed to occur in the Lower Jurassic of Poland. Among others, also the presence of marine pelecypods with Cardinia sp. has been ascertained in the Lower Pliensbachian, Liassic gamma (W. Karaszewski 1965, W. Karaszewski, J. Kopik 1969).The entire area is characterized by well developed brackish deposits of Lower Toarcian age (Ciechocinek series), which occur mainly as green claystones and siltstones with Estheria sp. and with ostracods.
Eastwards, a gradual decrease in the thickness of these deposits appears. Upper Toarcian, for example, quickly wedges out (Borucice series), from 145 m to several metres only. In the Lower Liassic two lowermost series, i.e. Zagaje series and Skłoby series (Hettangian), disappear completely. As a result of this, the thickness of the Liassic deposits in the eastern part amounts to about 100 m, i.e. only one tenth of the whole section in the zone of the complete development of the Liassic formations in the Świętokrzyskie Mts. Moreover, there was also possible to investigate the continuation of the large longitudinal dislocations that surrounds the Liassic formations from south-west and south. Along this dislocation the Liassic formations border either upon the Triassic, or upon the Palaeozoic.
The Liassic formations in the eastern portion, investigated in the last years by means of drillings, fill in a strongly elongated, narrow, tectonically disturbed zone, where dips amount approximately to 20- 45°. West of the Vistula river, the azimuth of this zone is as much as 110-l05°, and on the right river bank it deviates to reach 115°. The presence of this zone may be observed in the gravimetric picture as a decrease in the intensity of gravitational force, as compared with the adjacent areas. Most probably, a strongly dislocated zone occurs here, separating the massif of the Świętokrzyskie Mountains from the East-European platform. The Liassic deposits are cut by numerous transversal faults that frequently displace the outcrops of the individual series. In the westerly part, these faults as a rule run in NE-SW direction, to take, in the eastern part, gradually meridional direction. One of these faults (Fig. 1) separates the normally developed zone of Liassic outcrops (known already before) from its narrowed and dislocated continuation to the east.