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MIDDLE TRIASSIC EVOLUTION OF THE NORTHERN PERI-TETHYS AREA AS INFLUENCED BY EARLY OPENING OF THE TETHYS OCEAN Joachim SZULC Key words: Late Scythian-Carnian, Tethys, Peri-Tethys, basin analysis, sequence stratigraphy, paleogeography, paleoenvironments. |
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| Abstract: During Middle
Triassic times, the Germanic or northern Peri-Tethys Basin pertained to
the western Tethys Ocean. The basin was closed from the north and open toward
the Tethys by tectonically controlled depressions (gates). The gates were
opened in different times. The marine incursions broke first (as early as
in late Scythian time) through the eastern gates and from the Polish Basin
advanced gradually to the west. Semiclosed disposition of the basin resulted in its distinctive environmental diversification. Open marine environments developed along the southeastern margins which should be regarded as an integrate part of the Tethys Ocean rather than the epicontinental sea. Northward and westward from the Silesian and Carpathian domains the environments became more restricted. This resulted in significant facies diachronity between the western and eastern parts of the basin. As indicated by the faunal diversity, facies variability and geochemical properties of the sediments, during almost entire Anisian time the open marine sedimentation dominated in the eastern part while the western part displayed restricted circulation, typical for the semi-closed, evaporitic basin. The circulation reversed in Ladinian time when the westward shift of the tethyan spreading center gave rise to opening of the western gate. Meanwhile, the eastern and northern parts of the basin were uplifted and underwent emersion by the end of the Ladinian. Evolution of the southern parts of the Germanic Basin (Silesia, Holy Cross Mts., SW Germany) has been directly influenced by the Tethys rifts. The crustal motion was transmitted from the Tethys rift onto its northern periphery by reactivated Hercynian master faults. The Northern Germany and the North Sea basins were controlled by the North Atlantic-Arctic rift system. The central part of the basin was dominated by thermal subsidence. Despite of the intense synsedimentary tectonism affecting the basin, the distinguished 3rd order depositional sequences resulted from eustatic controls. The concordance between the tethyan and peritethyan sequence stratigraphy argues for the overregional, eustatic nature of the sequences. Faunal migration from the Tethys into its northern periphery followed generally the rift-controlled opening of the seaways within the Tethys. The first tethyan faunas which appeared in the south-eastern part of the Polish Basin as early as in Induan time came from the eastern branch of the Tethys Ocean (Paleo-Tethys). The next migration waves proceeded by western branches of the spreading ocean (Neo-Tethys) and entered the Germanic Basin through the Silesian-Moravian Gate (in Anisian time) and through the Western Gate from Ladinian time onward. |
Abstrakt: W czasie środkowego triasu basen germański należał
do północnego obrzeżenia Oceanu Tetydy nazywanego północną Perytetydą.
Taka pozycja paleogeograficzna wskazuje że basen germański należy traktować
raczej jako integralną część zachodniej Tetydy niż jako typowy basen
epikontynentalny. Bezpośrednie połączenie między obszarem germańskim
a Tetydą utrzymywane było przez system tektonicznie generowanych obniżeń
(bram) rozwiniętych w obrębie speneplenizowanego lądu windelicko-bohemskiego
stanowiącego strukturalną barierę między otwartym oceanem i jego strefą
peryferyjną.
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