Allostratygrafia a litostratygrafia czerwonego spągowca w Polsce

Abstract

Na podstawie dotychczasowych propozycji formalnego podziału czerwonego spągowca w Polsce przedyskutowano zasady wyróżniania jednostek lito- i allostratygraficznych oraz zaproponowano schematy stratygraficzne, które dają możliwość wszechstronnego podziału czerwonego spągowca.ALLOSTRATIGRAPHY VERSUS LITHOSTRATIGRAPHY OF THE ROTLIEGENDES OF POLAND A few proposals of formal lithostratigraphic subdivision of the Rotliegendes of Poland, put forward up to the present, may be divided into two groups: one, using distrophic, sedimentary cycles as the criterion for differentiation of units, and the other, based on lithological characteristics only. According to the Author, the differences in approach in the above subdivisions are mainly due to the strictness of the Polish stratigraphic principles, allowing for differentiation of only three categories of formal units, i.e. lithostratigraphic, biostratigraphic, and chronostratigraphic units. Thus, classification of the hitherto used units and giving them names turned to be the easiest way to formalize litho-stratigraphic units. This, of course, resulted in some misunderstanding as the lithostratigraphic units were differentiated on the basis of genetic features. This resulted in a necessity to reconcile various proposals of the subdivision of the Rotliegendes as the rejection of these schemes, based on a long tradition, seems inappropriate but, at the same time, their character makes it impossible to classify them as formal stratigraphic ones. This question may be solved by introduction of a new category of formal units, that is allostratigraphic units differentiated on the basis of a genetic interpretation, to the Polish stratigraphic principles. The Author proposes to accept the Dolsk Formation as the oldest of Rotliegendes formations (Table 1). It occurs between the folded Variscan basement or coal-bearing formations and volcanic rocks and comprises gray and black medium-grained sediments in lower part and mainly red-brown mudstones and claystones in the upper. This bipartity may be excellently used in the allostratigraphic subdivision by differentiation of the lower part (gray and black sediments) as the Kaczawa alloformation, and the upper (red-brown sediments) as the Kwisa allformation (Table 2). The Dolsk Formation is as a rule overlain by volcanic rocks, for which the name Wyrzeka Formation is here proposed. Boundaries of that formation would be delineated by the base of the first occurrence of volcanic reeks, and the top of the last one. Rocks genetically related to volcanic phenomena and as· signed along with volcanic rocks to volcanic-sedimentary cycles, fairly often occur within volcanic successions and sometimes also above them. The approach accepted here makes possible differentiation of one unit of the alloformation rank - a unit here names as the Barycz alloformation, and ascribing the allomember rank to individual volcanic episodes (Fig. 1). Rotliegend volcanic reeks are overlain by conglomerates (Książ Wielkopolski Conglomerate Formation) in marginal parts of the basin and around synsedimentary paleoelevations, and sandstones (Siekierki Sandstone Formation) and mudstones (Piła Claystone Formation) in central parts of the basin. The subdivision into these formations may be made more accurate by differentiation of two members: one (Polwica Conglomerate Member) at the base of the formations and the other (Solec Conglomerate Member) above (Fig. 2, Table 1). Within the proposed formations two alloformations may be differentiated on the basis of diastrophism-related cyclic sedimentation: an older, Drawa alloformation, and younger, Noteć alloformation (Fig. 2, Table 2). In the lithostratigraphic approach the upper boundary of the Rotliegendes is delineated at the base of the Copper-bearing Shale or Basal Limestone. In the genetic approach the boundary should be delineated along that of marine and continental sediments, not treating their colour as a decisive criterion (Fig. 3). The units briefly discussed above may be put together to obtain higher-order ones (Tables 1 and 2). All the lithostratigraphic units were named after towns or regions, and the allostratigraphic - after rivers. According to the Author, the specific differentiation of names given to individual stratigraphic categories and unequivocal discrimination of litho- and allostratigraphic units should enable working out of universal Rotliegendes subdivision and wide use of the units.