Południowo-zachodnia krawędź Fennosarmacji

Abstract

THE SOUTHWESTERN MARGIN OF FENNO-SARMATIAThe enormous progress of geological research in Poland makes possible a new precise determination of the geology of the border zone between the southwestern part of Europe with its folded structure, and the. northeastern part with its platform character (Fenno-Sarmatia). There have been prepared the following detailed maps of Poland: a gravimetric one, scale 1 : 1 0000 000 (A. Dąbrowski 1954) and a magnetic one, scale 1 : 1 000 000 (A. Dąbrowski and K. Karaczun 1956a). The magnetic research has disclosed a. shallow substratum of magnetically active rocks in northeastern Poland which belongs to the Russian platform; the depth of this substratum is from 0.3 to 5 km. In southwestern Poland; located in the forefield of this platform, this depth exceeds 10 km. It has also been. established that along the margin of the platform there extends a step, 30 to 90 km. wide, for which the depth of magnetically active rocks amounts to 5 to 10 km. Upon this step. there has developed a syncline, called the marginal syncline of the Russian platform (W. Pożaryski 1956). In order to ascertain the structure· of this syncline, two cross-sections were plotted by the method of reflection and refraction seismic methods; results of test drillings were also used (Fig. 2, Fig. 3). In this manner it has been verified that the marginal syncline has developed in the Upper Cretaceous simult8neously with the formation of the great middle Polis h anticlinorium. This anticlinorium was formed on the area of a deep and narrow sedimentation basin, called the Polish-Danish furrow, situated immediately ahead of the margin of the Baltic shield and the Russian platform. The anticlinorium was created by horizontal movements compressing the furrow; there followed a slight overthrust upon the platform along its margin. This overthrust appears distinctly in Pomerania and in southern Poland only, where the crystalline substratum lies at a shallower depth (Fig. 1).