Middle Cretaceous Planktonic Foraminifera Assemblages from the Aptian/Albian Boundary of Nizna Unit (Western Carpathians)
tefan Józsa
Commenius University, Faculty of Natural Sciences
Department of Geology and Paleontology
Bratislava, Slovakia
vyvrat@pobox.sk
Pieniny Klippen Belt represents a long narrow, arch-like structure situated between the Inner and Outer Western Carpathians. Studied sequences are parts of isolated klippen, tectonically folded into later flysch sediments. From seven outcrops, the most complete profiles have been selected as suitable for further observations: Ostrý vrch near Dlhá nad Oravou village and S of Vysoký grúň near Krivá village.
The Nizna Limestone represents a relict of fully eroded Urgonian platform with sequences containing deposits of upper slope and basinal margin.
This formation, dated on the basis of planktic foraminifera as uppermost Aptian, is composed of carbonate grainstones, rudstones, representing massive bodies of calciturbidites, and packstones, representing the intercalations of pelagic sequences.
Overlapping sediments are black cherts probably of the latest Aptian age, free of foraminiferal fauna and red foraminiferal packstones of the lowermost Aptian.
Biostratigraphic data enable to assign them to the following zones: Biglobigerninella barri (subzones: Biglobigeriella barri s.s. and Globigerinelloides algerianus), and Ticinella roberti. Allodapic parts of the Aptian sequence are poor on planktic forams (5 taxa), unlike the pelagic parts that were rich in more diverse planktic foraminiferal assemblage (10 taxa). Other microfossil groups were detected, too: benthic foraminifera (10 taxa), radiolaria (6 taxa), sponge spicules and ostracoda (undetermined). Planktic foraminifera of the lowermost Albian are again poorly diversified (4 taxa). The recovered fauna was also documented using SEM photography.