Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Nannofloral changes in the Oligocene deposits of the Ždánice Unit, Křepice-5 borehole (Flysch Belt of Western Carpathians, Czech Republic)
Abstract
The gradual changes of calcareous nannoflora in Oligocene deposits were studied in the Outer Flysch Carpathians, Zdanice Unit, Krepice-5 borehole. Calcareous clay intercalations of the Menilitic Formation, Sitborice Member provided rich nannofossils of very low species diversity. Assemblages are characterized by changeable predominance of species Pontosphaera latoculata, P. latelliptica, Reticulofenestra lockeri, R. minuta, Cyclicargolithus floridanus and Dictyococcites bisectus. This phenomenon reflects the unsettled paleoenvironmental conditions, especially salinity and sea-level fluctuations, and nutrient input. Moreover, bloom Reticulofenestra ornata that was observed in the highest part of the formation bears testimony to extreme ecologic conditions, probably low salinity and/orhigh nutrient levels. The presence of Helicosphaera obliqua and Cyclicargolithus abisectus indicate zone NP24, uppermost Middle to lower Upper Oligocene. The onset of Krosno lithofacies, lower part of the Zdanice-Hustopece Formation is well marked by different character of nannofossil content, such as higher species diversity and high number of reworked nannofossils from the older Upper Cretaceous and Paleogene strata. The presence of Helicosphaera recta indicates zone NP24 here, probably lower Upper Oligocene.
