Problemy formalnej litostratygrafii cyklotemów ewaporatowych na przykładzie cechsztynu

Ryszard Wagner

Abstrakt


SOME PROBLEMS OF FORMAL LITHOSTRATIGRAPHY OF EVAPORITIC CYCLOTHEMS AT THE EXAMPLE OF THE ZECHSTEIN

Summary
The works aimed at establishing a formal lithostratigraphic subdivision of the Zechstein with reference to the principles of cyclicity of evaporities were initiated in Lithuania in 1962. Subsequently there were formalized subdivisions of the strata in England (in 1974) and northern North Sea (in British sector in 1977, and the Danish and Dutch in 1980), whereas the traditional subdivision into cyclothems is still applied in FRG, GDR, Poland and central parts of the Zechstein Basin in the North Sea (British and Norwegian sectors). A new, formal subdivision was recently proposed for a unique zuber facies of the uppermost Zechstein in central parts of the Polish sedimentary basin (Table).
The analysis shows that the above formal lithostratigraphic subdivisions were established using the previously accepted informal subdivisions into cyclothems and often differ from the former in ascribing formed status to the traditional names only (as in the case of the Dutch subdivision). It should be also noted that the formal subdivisions established in individual countries differ in ranks ascribed to lithostratigraphic horizons. In the British and Danish subdivisions the group rank is given to the carbonate- evaporitic cyclothems, and that of the formations - to major lithostratigraphic zones, and in the Dutch subdivision, the rank of group is given to the Zechstein, that of formation - to cyclothems, and that of members - to lithological horizons.
The Zechstein cyclothems are characterized by facies markedly uniform throughout the whole central part of the European Basin. Therefore, establishing of formal subdivision seems pointless when aimed to match formal requirements only. The best example is that of the North Sea where instead of one subdivision (into cyclothems) there are used 5 different formal ones. The need for establishment of formal local subdivisions, coexisting with the traditional subdivision into cyclothems, may arise in the case of marginal parts of the Zechstein Basin. In these areas the variability in lithology is very high and the cyclicity of sedimentation often difficult to trace. Therefore, the use of formal local subdivisions may be justified in the case of marginal zone of the basin in England, NW part of the North Sea, the Fringe Basin (Netherlands), and the unique zuber lithofacies in Poland.

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