Dinoltagellate cyst record of the Eocene-Oligocene boundary succession m flysch deposits at Leluch6w, Carpathian Mountains, Poland

Abstract: Organic-walled dinoflagellate cysts from Eocene-Oligocene transitional deposits have been studied in a section at Leluchdw, Flysch Carpathians, Poland. The Eocene-Oligocene boundary, as based on dinoflagellate cyst distribution, is placed in the upper part of the Leluch6w Marl Member. The main biostratigraphic events associated with this boundary interval are the highest occurrence of Areosphaeridium michoudii and Areosphaeridium diktyopIokum, and the lowest occurrence of WetzelieIla gochtii. D stinct changes in dinoflagellate cyst assemblages and palynofacies across the Eocene-Oligocene b undary at Leluch6w imply a drop in relative sea-level within the Carpathian flysch basin that might correlate with a major eustatic fall during the earliest Oligocene. A drop in sea surface temperature is recognized prior to the Eocene-Oligocene boundary, and evidence is presented for an increase in nutrient level and decrease insalinity within the photic zone during the earliest Oligocene. The Eocene-Oligocene transition in the Flysch Earpathians is marked by a distinct facies change. The Upper Eocene is developed as turbiditic and/or hemipelagic, mainly light-coloured sediments, which were deposited in relatively well-oxidized settings at depths below the carbonate compensation depth (CCD). In contrast, dark-coloured bituminous deposits (the Menilite Beds sensu lato) represent he vower Oligocene. Pale-coloured marly deposits- the Sub-Menilitic Globigerina Marl- usually separate these two lithofacies (Leszczyflski 1997, fig. 2). Such a significant transformation of facies must have been related to prominent palaeoenvironmental changes in the Carpathian flysch sea. An attempt to reconstruct hese changes as recorded in the Leluchdw section was the objective of this study. For this purpose, the analysis of palynofacies and organic-walled dinoflagellate cyst (hereafter 'dinocyst') distribu-tion was applied, and the results have been compared to those from other Eocene-Oligo-cene transitional successions in more external tectonic units of the Flysch Carpathians. ~eological settin