Prace nad systematyzowaniem stratygrafii górnej kredy Polski (poza Karpatami i Sudetami)

Abstract

Przedstawiono w ogólnych zarysach aktualny stan stratygrafii kredy górnej w Polsce oraz ramowe propozycje formalnych wydzieleń litostratygraficznych na szczeblu formacji.

WORKS ON SYSTEMATIZATION OF STRATIGRAPHY OF THE UPPER CRETACEOUS IN POLAND (EXCEPT FOR THE CARPATHIANS AND SUDETY MTS)

The whole epiplatform Upper Cretaceous of Poland belonged to the Boreal Zone. The analysis of faunal groups such as ammonites, belemnites, inoceramids and foraminifers made it possible to establish biostratigraphic subdivisions subsequently used for establishing chronostratigraphic scheme usable for the whole extra-Carpathian Poland (Table 1). The analysis also gave the basis for correlations with Boreal sections of the western Europe (Table 1).

The question of formal establishment seems limited to some of the zones presented here only. Lithostratigraphic units hitherto proposed for the Upper Cretaceous of extra-Carpathian Poland (Table 2) usually lack a precise definition. The lithostratigraphic and biostratigraphic units were given geographic names or letter and number denotations. All thCSll units are informal in the light of currently accepted principles of stratigraphic classification, terminology and nomenclature (S. Alexandrowicz and others, 1975) and the majority of hitherto proposed names seem unuseful (those marked with crosses in Table 2).

It is proposed to differentiate only a few formal formations for the Upper Cretaceous (including Albian) of Poland (except for the Carpathians and Sudety Mts). The formations are represented by four types of litho logical complexes defined by rocks predominating in them; I - sandy formation with predominance of sands and sandstones, II - siltstone-clay formation, III - formation of limestones, marls, opokas and gaizes, and IV - chalk formation. The use of these complexes will make possible lithological correlation on relatively large distances (Table 3, Fig. 1).

The classification proposed here seems also valid from the point of view of illustration of the degree of lithological differentiation on well logs.

It seems inappropriate to introduce a more detailed subdivision into .formations. In the case of the Upper Cretaceous, the same effect may be obtained by using units of the member or bed rank, differentiated within the above mentioned basic units of the lithostratigraphic subdivision. At the same time this approach limits the upbuilding of the nomenclature and, therefore, makes the classification more universal.

The above problems were discussed on the meeting of Cretaceous stratigraphers in October, 1978. The discussions proceeding there resulted in changes and supplementation of the first draft of the report as well as in taking some organizational measures concerning further works on systematization of iithostratigraphy of the epicontinental Upper Cretaceous in Poland.