Ewolucja basenów fanerozoicznych wzdłuż strefy Teisseyre'a-Tornquista

Abstract

Opracowanie jest analizą 66 map litofacjalno-paleogeograficznych, wykonanych w ramach Projektu IGCP nr 86. Paleogeografia obszaru była kontrolowana przez tarczę: fennoskandzką i ukraińską oraz dwa mniejsze masywy. Między tymi jednostkami rozwijały się drogi połączeń z wnętrzem platformy wschodnioeuropejskiej. Strefa T-T oddziaływała stale na rozkład lądów i mórz, a przede wszystkim na zróżnicowanie subsydencji i środowisk sedymentacji w basenach, przy czym jej segment polsko-bałtycki był z reguły najsilniej obniżony. Wyróżniono trzy etapy ewolucyjne obszaru: kambr-środkowy namur, późny namur-trias, najmłodszy trias-czwartorzęd. Główne transgresje pierwszego i trzeciego etapu byty warunkowane eustatycznymi zmianami poziomu mórz. Rozpatrzono podobieństwa w przebiegu niektórych transgresji i zależności między poszerzaniem i kurczeniem zbiorników a zmianami tempa sedymentacji.

PHANEROZOIC BASINAL EVOLUTION ALONG THE TEISSEYRE-TORNQUIST ZONE

Phanerozoic basins situated along the Teisseyre-Tornquist tectonic zone (T-T Zone) have been analysed in respect to their extent, subsidence and sedimentary environments. Palaeogeographic evolution NE of this zone (Fig. 1) was controlled by two Precambrian shields (Fennoscandian and Ukrainian) and by two smaller massives (Mazury-Byelorussian and Łuków). This pattern implies the subdivision of the T-T Zone into three segments: Scandinavian, Polish-Baltic and Ukrainian.

The Polish-Baltic segment was, as a rule, most downwarped and most easily surmounted by the expanding basins which in the periods of maximum extent were linked to the internal parts of the East European Platform by three ways: Baltic Syneclise, Podlasie Graben and Wolhynian Strait. A selection of palaeogeographic sketches is shown in Figs. 2-29, whereas Fig. 30 summarizes the results. Three stages have been distinguished in the evolution of the area: 1 - (Cambrian - Early Namurian) - domination of the marine environment, frequently of deep shelf and slope; 2 - (Middle Namurian - Triassic) - variable conditions, from paralic-limnic sedimentation in restricted basins through emersion and erosion to the accumulation of red-beds and evaporites; 3 - (latest Triassic - Tertiary) - domination of the paralic and shallow shelf environments. During the first stage the area was strongly influenced by oceanic domains which reflects the dispersal of continents in pre-Pangean times. The late Caledonian epoch was characterized by a strong downbending of the platform edge coupled with turbidite sedimentation while the post-Caledonian one - by a marked differential subsidence of this edge, accompanied first by fluvio-deltaic and then by marine sedimentation. The second stage resulted from the late Hercynian events in the adjacent orogenic belt and its subsequent intense erosion. It corresponds well with the Pangean epoch of the Earth's history. The third stage reflected the oscillatory transgressions of the epicontinental seas entering the peri-T-T Zone sedimentary trough both from the Tethyan and the North Atlantic provinces.

Major marine transgressions in the first and third stages, culminating in the mid-Cambrian, Late Ordovician, Early Silurian, Frasnian, Oxfordian and Turonian times, as well as their intervening regressions in the Late Cambrian, Ashgillian, Early Devonian, Late Toarcian-Aalenian, earliest Cretaceous and earliest Tertiary times were probably the effect of global, eustatic sea-level changes. There was striking similarity between the courses of some of these transgressions: their initial phases (Tremadocian, Callovian and Albian) resulted in a very condensed. predominantly clastic sedimentation. They were followed by a phase of accelerated subsidence and of a growth of vast carbonate platforms. Expansion of the basin was not necessarily connected with the marine transgression. Contrarily. the basinal shrinking was sometimes accompanied by the marine incursion and frequently - by the acceleration of subsidence. The T-T Zone was continuously acting as a geomorphic feature, either dividing the land areas from the sedimentary basins or - more often - governing the differential subsidence and sedimentary patterns within the basins.