Rola ruchów kaledońskich i hercyńskich w rozwoju tektonicznym obszaru nadbałtyckiego

Abstract

ROLE OF CALEDONIAN AND HERCYNIAN MOVEMENTS IN THE TECTONICAL DEVELOPMENT OF THE PERI-BALTIC AREA

Summary

In the Peri-Baltic area, the Caledonian type of tectogenesis can be characterized by three highly distinct turning-points in the tectonical development before the Middle-Upper Cambrian, Lower Silurian and Lower Devonian sedimentation. The Lower Cambrian structural plan is characterized by the presence of Lower Niemen and Łoknowskie elevations, which are lacking the lower Cambrian formations. Here, on the Pre-Cambrian substratum immediately rest Jurassic formations. Both elevations were surrounded with some lowerings filled in with terrigenous Lower Cambrian formations. Such a structural plan was buried under the deposits of Middle-Upper Carboniferous and Ordovician age. At the close of Ordovician the Lower Niemen massif was slightly denuded, whereas the Łoknowskie elevation was not. The Late Ordovician structural plan was then discordantly covered with the deposits of the lowermost Silurian. At the Venlockian time the Peri-Baltic syneclise was formed. The syneclise probably included greater part of the Baltic area, as well as the area of the present Byelorussian-Mazury anteclise and Brest depression. At the decline of the Caledonian phase the Peri-Baltic syneclise was uplifted and underwent denudation, mainly in the elongated, east-west trending elevation zones. Then, the area was disocordantly covered with the Lower Devonian deposits. Beginning with this time, a new phase in the lowering process began in the Peri-Baltic syneclise and in its surrounding regions, lasting up to the latter half of the Carboniferous period. In the Baltic area, the Hercynian uplifting movements at the Carboniferous time distinctly changed the structural plan of the region considered. The Byelorussian-Mazury anteclise was intensely elevated, separating the Peri-Baltic syneclise into two depressions: Polish-Lithuanian depression in the north, and Brest depression in the south. Within the Byelorussian-Mazury anteclise the Palaeozoic deposits were completely denuded, and the rocks of the crystalline basement were exposed. In both Polish-Lithuanian and Brest depressions the denudation process was slighter than at the decline of the Caledonian phase. The final, Late Hercynian phase of tectonic movements was, in the Peri-Baltic area, of fundamental importance mainly for development of local structures which area interesting as concerns search for oil and gas deposits.