Wkład badań geofizyki powierzchniowej w rozpoznanie budowy geologicznej niecki warszawskiej

Abstract

THE CONTRIBUTION OF SURFACE GEOPHYSICAL SURVEYS TO THE KNOWLEDGE OF GEOLOGICAL STRUCTURE OF THE WARSAW BASIN Summary The results of surface geophysical surveys are characterized with reference to the available information on geological structure of the Warsaw Basin. Moreover, the methodological possibilities of more complete interpretation of data obtained with the use of individual methods are outlined. The structural character of the Warsaw Basin area is mainly revealed by reflection seismics. Seismic surveys showed general south-westwardip of sub-salinary basement, the accompanying increase in thickness of Zechstein-Jurassic series as well as presence of several structural forms. The area of the Warsaw Basin is characterized by marked predominance of anticlinal structures. The structures are arranged in elongate structural lines, parallel to the basin axis and, therefore, to the margin of the East-European Precambrian Platform. Some of these structures are related to salt tectonics. Anticlines and anticlinal bends are usually situated in the proximity of dislocation zones. The recorded correlations in arrangement of structures evidence genetic relations between the structures and faults in the sub-salinary and deeper-seated horizons. Major dislocations are set parallel to axis of structural lines and, thus, to the Platform margin. Dislocations are usually more common and intense in lower parts of the Zechstein-Mesozoic complex than in the upper. The characteristic structural elements of this area include, besides dislocations, tectonic troughs. Faults of regional nature were also found. The analysis of seismic data showed marked bipartity of the Warsaw Basin. The boundary of its south-western part (marginal zone of salt tectonics) and the north-eastern (zone of block tectonics) is of the fault type. Below the boundary Z1, the seismic profiles do not display any dynamic reflections which could give information on structure of deeper-seated strata. Gravimetric image of the Warsaw Basin is genetically highly complex. The major sources of gravity anomalies include: petrographic differentiation of crystalline basement, elements of its morphology and the shape of various complex boundaries of density contrasts in sedimentary series (effect of compensation for salt structures). The review of available geophysical data showed that the origin of the recorded gravity anomalies cannot be analysed for the whole area of the Warsaw Basin. The area should be divided into the platform (Precambrian) part and that situated south-west of the platform margin. It should be noted that the presented interpretation of the magnetic and gravimetric images of the contact zone of the platforms fully agrees with the model of consolidated basement, established on the basis of refraction data. The paper presents preliminary results of complex qualitative interpretation of geophysical maps. The interpretation made it possible to trace and explain main relationships between geological structure and the recorded geophysical phenomena. On the basis of geophysical data, several methodological conclusions may be also drawn. Further geophysical surveys should be aimed at further development in methods of studies, especially reflection studies. Refraction profilling may be carried out in order to recognize morphology and tectonics of deep-seated consolidate basement. The aims of further use of gravity and magnetic methods should not be connected with providing continuity of measurements but rather interpretation of the available data, combined with correlation with seismic data.