Tektonika i ewolucja paleotektoniczna paleozoiku podpermskiego między Koszalinem i Toruniem (Pomorze)
Abstract
TECTONICS AND PALEOTECTONIC EVOLUTION OF THE PRE-PERMIAN PALEOZOIC BETWEEN KOSZALIN AND TORUŃ (POMERANIA)
Summary
The tectonic structure of pre-Permian Paleozoic in the platform contact zone between Koszalin and Toruń was reanalysed mainly on the basis of data from deep drillings and refraction seismics surveys. In this area, Paleozoic complexes occurring in the foreland of the East-European Precambrian Platform differ from those of sedimentary cover of the latter in thickness, facies development, tectonic history as well as style and directions, and appearance of Upper Silurian - Devonian - Carboniferous cover. A special attention should be paid to band-like pattern of blocks, roughly parallel to margin of the East-European Platform. Besides eventual Grampian stage, here may be differentiated two structural stages of pre-Permian Paleozoic. Lower stage is built of strongly deformed Ordovician and Lower Silurian rocks, and the upper - of Upper Silurian, Devonian and Carboniferous ones. The lower stage appears the thickest (5000-6000 m thick) in blocks situated in direct foreland of the East-European Platform and refraction seismics data show (Fig. 2) that it suddenly thins out to about 3000 m or less at a line running about a dozen to 25 km SW of the platform margin. Together with negligible thickness of the Ordovician in marginal part of the East-European Platform (15) this gives the appearance of synsedimentary trough for the zone of increased thickness of the Ordovician and Lower Silurian (17).
The age of disturbances or foldings of rocks belonging to the lower structural stage remains the subject of discussions. However, in the light of the available data it may be stated that the peak of deformations dated at the tum of, the Wenlockian and Ludlovian (2) seems more probable than any phase from the tum of the Silurian and Devonian or early Devonian (5). The Mid-Silurian and not younger age of these disturbances is primarily suggested by the continuity of sedimentation at the tum of the Silurian and Devonian, recorded in the Radom - Lublin sector of the contact zone of the East- European -Precambrian and Mid-European Paleozoic Platforms (12), and cover character of Upper Silurian-Lower Devonian sequences in relation to disturbed Lower Silurian and older ones in the Radom region. Disturbances of the Lower Paleozoic in the foreland of the East-European Platform seem connected with deep crustal fractures of the strike-slip fault type and not the existence of Central-European branch of the Caledonian geosyncline (see also (8)). Such interpretation does not exclude overthrust of these disturbed series on the platform margin. However, such overthrust still remains to be proven.
In the Koszalin - Toruń zone, the Upper Silurian - Devonian - Carboniferous cover displays very clearly effects of Variscan błock movements. Displacements traceable in basal surface of the Zechstein approach merely 100-200 m whilst those connected with pre-Zechstein block movements may range from about 500 m to some kilometers. Therefore, it should be stated that błock movements acting here after the Early Permian did not exort any significant influence on structural -character of pre-Permian Paleozoic.
Summary
The tectonic structure of pre-Permian Paleozoic in the platform contact zone between Koszalin and Toruń was reanalysed mainly on the basis of data from deep drillings and refraction seismics surveys. In this area, Paleozoic complexes occurring in the foreland of the East-European Precambrian Platform differ from those of sedimentary cover of the latter in thickness, facies development, tectonic history as well as style and directions, and appearance of Upper Silurian - Devonian - Carboniferous cover. A special attention should be paid to band-like pattern of blocks, roughly parallel to margin of the East-European Platform. Besides eventual Grampian stage, here may be differentiated two structural stages of pre-Permian Paleozoic. Lower stage is built of strongly deformed Ordovician and Lower Silurian rocks, and the upper - of Upper Silurian, Devonian and Carboniferous ones. The lower stage appears the thickest (5000-6000 m thick) in blocks situated in direct foreland of the East-European Platform and refraction seismics data show (Fig. 2) that it suddenly thins out to about 3000 m or less at a line running about a dozen to 25 km SW of the platform margin. Together with negligible thickness of the Ordovician in marginal part of the East-European Platform (15) this gives the appearance of synsedimentary trough for the zone of increased thickness of the Ordovician and Lower Silurian (17).
The age of disturbances or foldings of rocks belonging to the lower structural stage remains the subject of discussions. However, in the light of the available data it may be stated that the peak of deformations dated at the tum of, the Wenlockian and Ludlovian (2) seems more probable than any phase from the tum of the Silurian and Devonian or early Devonian (5). The Mid-Silurian and not younger age of these disturbances is primarily suggested by the continuity of sedimentation at the tum of the Silurian and Devonian, recorded in the Radom - Lublin sector of the contact zone of the East- European -Precambrian and Mid-European Paleozoic Platforms (12), and cover character of Upper Silurian-Lower Devonian sequences in relation to disturbed Lower Silurian and older ones in the Radom region. Disturbances of the Lower Paleozoic in the foreland of the East-European Platform seem connected with deep crustal fractures of the strike-slip fault type and not the existence of Central-European branch of the Caledonian geosyncline (see also (8)). Such interpretation does not exclude overthrust of these disturbed series on the platform margin. However, such overthrust still remains to be proven.
In the Koszalin - Toruń zone, the Upper Silurian - Devonian - Carboniferous cover displays very clearly effects of Variscan błock movements. Displacements traceable in basal surface of the Zechstein approach merely 100-200 m whilst those connected with pre-Zechstein block movements may range from about 500 m to some kilometers. Therefore, it should be stated that błock movements acting here after the Early Permian did not exort any significant influence on structural -character of pre-Permian Paleozoic.