The nannofossil biostratigraphy of the youngest deposits of the Magura Nappe (East of the Skawa river, Polish Flysch Carpathians)

Marta Oszczypko-Clowes


Biostratygrafia i warunki paleośrodowiskowe najmłodszych osadów płaszczowiny magurskiej na wschód od Skawy w oparciu o nannoplankton wapienny (polskie Karpaty fliszowe)

The Magura Nappe is the largest and southernmost tectonic unit of the Western Outer Caipathians and differ in lithofacies development from the Middle and Marginal groups of units. The age studies of the youngest deposits of the Magura Nappe play an important role in understanding the tectogenesis of the Outer Carpathians. The aim of this work was to find the litho- and biostratigraphic correlation with the more external units. For this purpose the youngest deposits from selected sections of the Magura Nappe located east of the Skawa River, were chosen. For the lower limit of the youngest sediments, Middle/Upper Eocene variegated shales with Reticulophragmium amplectens Grzybowski were taken. The analysis of nannoplankton assemblages enable to establish the age of these deposits which varies from Middle Eocene (NP15) up to Upper Oligocene (NP25) and Lower Miocene (NN2). The Eocene/Oligocene boundary lies within the NP21 nanno-zone and was found in the Krynica Zone within the Globigerina Marls (Leluchów section), in the Raca Zone within Poprad Sandstone Mbr of the Magura Fm. and in the Siary Zone within supra-Magura (Budzów) Beds (Budzów section), Wątkowa Sandstone (Ropica and Małastów sections) and within Zembrzyce (sub-Magura) Beds (Folusz section). In the Raca and Krynica zones the youngest - Upper Oligocene deposits from the studied sections belong to the Malcov Fm., whereas in the Siary Zone they belong to the supra-Magura (Budzów) Beds. The age of the Malcov Fm. was determined as NP24 in Leluchów and as NP25 in the Nowy Sącz I borehole, whereas the Budzów Beds belong to zone NP24. The youngest deposits so far described from the Magura Nappe belong to the Zawada Fm. whose age was determined as NN2. In the Polish part of the Bystrica Zone deposits younger than NP18, have so far not been found. The analysis of autochtonous nannoplankton assemblages from the Magura Basin enable to follow the palaeoecological changes in the Magura Basin, both in regional and global sense, from Late Eocene through Oligocene. The global changes are the drop of the water temperature accompanied by the progressing eutrophication of the Magura Basin. Further events were also recorded in zone NP23. The assemblage of this zone was characterised by the presence of species which are believed to be indicative of brackish water and restricted to the Paratethys region.

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