Uwagi o podłożu permu w Wielkopolsce

Abstract

 Przedstawiono szkic litologii i stratygrafii utworów podpermskich na obszarze Wielkopolski. Na podstawie przeanalizowanych profilów można sądzić, że poza główną fazą fałdowań waryscyjskich (namur B–D) w najwyższym karbonie zachodziły intensywne ruchy tektoniczne. Były one prawdopodobnie związane z głębokimi rozłamami. Obecny obraz powierzchni podpermskiej, poza morfologią, jest efektem działalności tektonicznej w górnym karbonie i dolnym permie, połączonej z silną erozją. SOME REMARKS ON BASEMENT OF THE PERMIAN IN THE WIELKOPOLSKA REGION The oldest rocks encountered beneath the Permian in the Wielkopolska region are sericite-chlorite schists, quartzites and phyllites with dips ranging from 20° to 90°. Sporomorphs extracted from these rocks suggest their Lower Paleozoic age. Both in the south and north, there is found contact of the Lower Paleozoic rocks and deposits developed as dark-gray with violet shade, alternating sandstones and shales with dips varying in the range from 20° to 90°. The record of goniatitids and miospores shows that the latter mainly belong to the Lower Carboniferous (including Namurian A).In basal part of borehole column Donatowo 1 (Fig. 1), Lower Permian volcanic rocks and folded Lower Carboniferous basement are separated by weakly diagenesed gray sandstones. The sandstones are intercalated by dark-gray mudstones rich in carbonized plant remains and miospores. The youngest of the identified spores indicate Stephanian age of these rocks (Table 1; Table I). Above the gray rocks, there begin to appear intercalations of red claystones and finally the whole rock changes colour to red-brownish. The rocks dip at the angle close to 20° and the whole series is overlain by brown-violet claystones with dip ranging from 0° to 5°.The above examples indicate a marked angular unconformity between folded Lower Carboniferous and Upper Carboniferous. Another angular unconformity may be traced at the boundary of the Carboniferous and Permian (Figs. 1, 2). However, it cannot be excluded that tectonic disturbances involving the Upper Carboniferous are of local character only, being related to deep crustal fractures. It should be noted that the Lower Carboniferous basement is covered by flat-laying dark-gray clay shales in borehole columns merely 20–30 km distant from a center of volcanic eruptions, founded on the Dolsk deep crustal dislocation.The occurrence of Lower Paleozoic rocks (which presumably represent an axial part of anticlinal uplift) at sub-Permian surface is delineated in the east by the Poznań–Oleśnica dislocation zone which also represents western limit of distribution of Upper Carboniferous cover (Fig. 3).