Podział tektoniczny i paleotektoniczny niecki pomorskiej

Abstract

Analiza nowszych przekrojów sejsmicznych i głębokich wierceń ujawniła, że w niecce pomorskiej można wyróżnić 3 podłużne strefy o różnym stylu tektonicznym i różnej ewolucji w permo-mezozoiku. Dwie strefy, zachowujące się sztywniej (A i C), przedzielone były strefą ruchliwszą i tektonicznie bardziej urozmaiconą (strefa Koszalina - Chojnic s.s.). Niektóre z walnych uskoków ograniczających te strefy mogą mieć założenia starsze. W strefie A w późnym triasie, jurze i dolnej kredzie wykształciło się paleowypiętrzenie (garb Wielimia) o zredukowanych miąższościach i silniej zaakcentowanych łukach erozyjnych w porównaniu u strefą Koszalina - Chojnic z jednej i walem pomorskim z drugiej strony. Wykazuje ono podobieństwo do garbu wielkopolskiego, wyróżnionego wcześniej w Polsce środkowej.

TECTONIC AND PALAEOTECTONIC SUBDIVISION OF THE POMERANIAN TROUGH

Recent reflection seismic and borehole data have been used for reconstruction of the tectonic' and palaeotectonic evolution of the Pomeranian Trough (northwest Poland). Three elongated zones, parallel to the strike of the trough, have been distinguished, each of them being characterized by its own tectonic style and by specific thickness of the Permian-Mesozoic structural complex (Figs 1, 2). A mobile zone B is bordered from both sides by more stable zones: A and C (Fig. 2, IV – IV'). Their boundaries are defined by major fault systems, some of which are probably deeply rooted. It is evidenced by their correlation with fractures in the consolidated basement (Fig. 1), encountered by the seismic refraction method. The northeasternmost fault system: Sianów - Polanów - Stobno - Świecie separates the Pomeranian Trough from the Łeba Uplift -a part of the Precambrian Platform. At the opposite side the trough is bounded by the fault system Szczecinek - Debrzno from the Pomeranian Swell - a young uplifted unit which was formed due to Early Tertiary inversion of the northwest segment of the Mesozoic Mid-Polish Furrow.

Zone A revealed an upwarping trend during the Late Triassic -Early Cretaceous time span. It is expressed by the reduced thickness of individual stages and formations as well as by the increase of stratigraphic-erosional gaps which marked main diastrophic events at the boundaries between Triassic and Jurassic, Early and Middle Jurassic, and Jurassic and Cretaceous (Figs 3, 4). The palaeotectonic significance of this zone (called here the Wielimie Ridge) is thus comparable with that of the Wielkopolska Ridge, identified earlier at the opposite side of the Mid-Polish Furrow along its Kujawy segment.

Subdivision of the Pomeranian Trough into zones: A, B and C is partly incompatible with the previously proposed subdivision into tectonic units of Kołobrzeg, Koszalin and Tuchola (Fig. 1, inset map). The elements of both subdivisions should be used during future work, the relation of the Kołobrzeg unit to the adjacent ones being the most vital problem to be solved.