Styl strukturalny kompleksu cechsztyńsko-mezozoicznego na niektórych obszarach Niżu Polskiego

Abstract

STRUCTURAL STYLE OF THE ZECHSTEIN-MESOZOIC COMPLEX IN SOME AREAS OF THE POLISH LOWLANDSummary The present paper deals with the tectonical problems at the Zechstein-Mesozoic structural complex. Fundamental data are from seismical survey and numerous deep drillings made in the last years. Both geological cross sections (Figs. 1–6) and a sketch map of distribution of various genetical types of local structures (Fig. 7) illustrate the problem considered.The present form of the complex is mainly due to the vertical movements of the pre-Zechstein substratum blocks. These movements were of relatively small amplitude, their course being slow, but – generally speaking – uninterrupted.The effect of their activity was of double nature. First – these movements differentiated, together with the sedimentation, its rate and character. The differentiation may have been regional or local, and the thicknesses may have changed along wide or short distances. Second – the vertical movements were responsible for a structural reworking of the complex, particularly at the Cretaceous –Tertiary boundary. The close relation between the tectonical and sedimentary processes, whose genesis was the same, led in turn to the development of particular features of the complex under consideration. Some examples are given in the geological cross sections. Placanticlinal folds (superficial and reflected structures in American terminology) are of various folds in various horizontal planes (Figs. 1, 2a, 3). Consedimentary falut zones may be characterized by various amplitudes, and even by an opposite direction of throw at various depths (Figs. 1, 2a. 3, 5 a-c). Faults that are numerous in the lower portions of the complex may, frequently, die out upwards (Figs. 1–6). The structural outlines of the higher horizons may partly or completely differ from those of the lower horizons. In the simplest cases, the structural reworking may have intensified, compensated or led to inversion of deep structures. If, however, the zones of the strongest subsidence moved gradually, the relation between various structural plans would be more complicated.The effects of the processes mentioned above may easily be identified in the marginal part of the Zechstein saliferous basin. The farther we approach the central part of the basin, the stronger are the influence and intensity of salt movements that have modified both local sedimentary conditions and local tectonic activity (Figs. 4, 5 d-e, 6). These phenomena obliterated the influence of the vertical movements of the substratum blocks. However, the directions of the local structures and their chains seem to depend upon the deep fault zones here.There is a distinct genetical zonal arrangement at the local structural elements in the basin in study. In the central part of the area pierced and half-pierced salt plugs and salt ramparts are found. This area is surrounded by a zone of salt pillows and salt lenses, this in turn – by a zone of block and placanticlinalm structures (Fig. 7).Deep zones of tectonical discontinuities are the most important elements in the discussion of the tectonical problems of the complex. There zones should be a basis for horizontal subdivision of the complex. The so far accepted boundary of the main structural unit, i.e. of the Kujawy – Pomeranian swell (the sub-Cainozoic outcrop of the Lower and Upper Cretaceous boundary), seems to be accidental at places, mainly due to a fact that it is affected by various regional and local factors (Fig. 7).The intrinsic structure of the Zechstein – Mesozoic complex is undoubtedly of platform, organogenic type, and does not reveal any features of compression folding. There is no basis for a vertical subdivision of the complex, for there are lacking phenomena of both Old-Cimmerian and Young Cimmerian “orogenic” phases.