Obecny podział litostratygraficzny epikontynentalnej kredy dolnej w Polsce i propozycje jego uporządkowania

Abstract

Przedstawiono propozycje podziału litostratygraficznego epikontynentalnej kredy dolnej w Polsce w rozbiciu na dwa regiony: A i B (tab. 1 i 2). Opracowanie dotyczy głównie starszej kredy dolnej oraz stanowi uzupełnienie istniejącego podziału młodszej kredy dolnej w Polsce północno-zachodniej i środkowej, dokonanego w 1979 r. przez A. Raczyńską. W regionie A zaproponowano wyróżnienie formacji : kcyńskiej, rogoźniańskiej, włocławskiej i mogileńskiej (tab. 1), zaś w regionie B – formacji cieszanowskiej, białobrzeskiej i mogileńskiej (tab. 2).

LITHOSTRATIGRAPIDC SUBDIVISION OF EPICONTINENTAL LOWER CRETACEOUS·IN POLAND AND PROPOSALS FOR ITS REARRANGEMENT

The facies development d epicontinental Lower Cretaceous makes it necessary to differentiate two regions partly differing in lithostratigraphic subdivisions (Tables 1, 2). The region A comprises north-western and central Poland, and the region B - the Lublin area.

It is proposed to divide older Lower Cretaceous of the region A into three formations, with reference to lithostratigraphic subdivision of the younger Lower Cretaceous d the north-western and·central Poland (A. Raczyńska, 19790):

I - Kcynia Formation, mainly comprising deposits of Jurassic Purbeck facies which win be treated together with other parts of the Upper Jurassic. The uppermost part of this Formation comprises the lowermost Lower Cretaceous.

II - Rogoźno Formation, comprising marine Berriassian and clay, lower part of Lower Valanginian.

III - Bodzanów Formation, comprising upper, sandy part of Lower Valanginian.

The Włocławek (Upper Valanginian and Hauterivian) and Mogilno (Barremian - Middle Albian) Formations were previously differentiated.·

Boundaries of these formations are essentially clearly marked throughout the north-western and central Poland except for some parts of the Warsaw Basin, where the boundary between the Formations II and III becomes obliterated and the Formation II may be wedging out. Moreover, several members with horizontal extent narrower than that of formations were differentiated in some of them (Table 2). In the region B, it is proposed to use the same Dame of Mogilno Formation for the youngest deposits presumably belonging to the Barremian - Middle Albian. The Neocomian may be divided into two formations: upper - Białobrzegi Formation (clay-siltstone-marly; Upper Valanginian-Hauterivian) and lower - Cieszanów Formation (limestone-marly; Berriasian - Lower Valanginian).