Zarys stratygrafii kredy dolnej Kujaw

Sylwester Marek




The most complete development of the Lower Cretaceous deposits within the Polish Lowland area is observed in the Kujawy region, where their thickness amounts to 600 metres. The richest fauna assemblage, particulary that of ammonites, is also related to the region considered (Figs: 1, 2, 3 and 4). At the Riasanian time, a transition took place from the first marine ingression within the Purbeckian fresh-water basin, into a typical marine sedimentary environment with ammonite fauna of Riasanites rjasanensis (Wenetzky) Lahusen, Berriasella cf. euxina (Ret.), B. cf. lorioli (Zitt.), B. ct. pontica (Ret.), Himalayites cf. cortazari (Ret.), Neocomites sp., Neocosmoceras cf. sayni (Sim.), Euthymiceras cf. euthymi (Piet.) and with scarce forms that reveal a great similarity to the boreal species such as Surites spasskensis (Nik.), S. subtzikwinianus (Bogosl.) and S. kozakowianus (Bogosl.). The Riasanian transgression entered the Kujawy region from south-east. The Lower Valanginian is a continuation of the Riasanian marine sedimentary regime. The ammonite fauna of Platylenticeras and Polyptychites, found in this area, connects the Kujawy sedimentary basin of Lower Valanginian age first of all with the Anglo-Germanic basin, whereas the southern influences are expressed by the presence of the genus Neocomites (Table I, Fig. 5). The Middle Valanginian deposits of the Kujawy region show distinct influences of marine sedimentation of siltstone-clayey type only in the transition parts, from the Lower Valanginian on the one hand, to the Upper Valanginian, on the other. The central arenaceous portion of the complex reveals the features of a near-shore sediment. This allows us to state that the Middle Valanginian basin was partly isolated, where marine conditions governed periodically, directed from north-west and south-east. At the Upper Valanginian time the marine regime reappeared. The whole sedimentary complex reveals highly abundant ammonite fauna, among others Dichotomites bidichotomus (Leym.), Table III, Fig. 16, D. cf. bidichotomus (Leym.), Table I, Fig. 9, Table II, Fig. 14, D. sp. ex gr. bidichotomus, Table II, Fig. 13, D. cf. petschorensis (Bogosl.), Saynoceras verrucosum d'Orb., Table III, Fig. 18, (?) Saynoceras sp., Table III, Fig. 15, Leopoldia provincialis Sayn., Neocraspedites complanatus (Koen), Table III, Fig. 17, Astieria sp, and Polyptychites cf. nucleus (Roem.), P. cf. ramulicostanus Pavl., Table II, Fig. 12, P. cf. michalskii (Bogosl.), Table I, Fig. 6, Table II, Fig. 11, Neocomites cf. neocomiensis d'Orb., Table I, Fig. 8. This no doubt is an assemblage of Upper Valanginian ammonites known to occur also in the Neocomian deposits of England, Germany and Russia. The Lower Hauterivian deposits evidence a continuation of the marine regime that began already at the Upper Valanginian time. The ammonite fauna (Endemoceras cf. noricum (Roem.) - Table III, Fig. 22, Endemoceras sp. ex gr. Noricum (Roem.) - Table III, Fig. 21 and Neocraspedites cf. carteroni d'Orb.) links the Kujawy sedimentary basin with the seas of both the Boreal and Mediterranean provinces. At the Upper Hauterivian time, an interruption in connection with the Mediterranean basin took probably place. Sligth marine influence at the Upper Hauterivian time left behind a poor pelecypod and foraminifer fauna, typical rather of the West-European basin. The arenaceous deposits of Barremian - Middle Albian age represent a new cycle of transgression during the Lower Cretaceous sedimentation. Petrographical sedimentation suggests that these deposits have been laid down in a marine basin, under near-shore conditions and within estuarine flats.

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