Palaeoenvironment of the Eocene-Oligocene of the northern Ukraine in the light of palynological analysis and comparison with coeval Carpathian strata

Eocene-Oligocene sequence of the northern Ukraine consists of diversified, mainly non-calcareous clastic deposits representing following lithostratigraphic units: Kanev Formation (?Ypresian), Buchak Formation (Lutetian), Kiev Formation (Upper Lutetian Bartonian), Obuhov Formation (Priabonian), Mezhigor Formation (Rupelian) and Bereka Formation (?Chattian).
   We compared results of palynofacial analysis (i.e., composition of organic remains of marine and terrestrial origin) and taxonomical diversity of aquatic palynomorphs representing both marine and freshwater taxa. Our palynological analysis revealed variable sedimentological settings of these deposits reflecting various palaeoenvironments.
   The oldest investigated strata (the Kanev Formation) contain high ratio of marine dinoflagellate cysts (occasionally up to 90%) pointing to marine environment optimal for development of rich and diversified dinoflagellate flora during the Early Eocene (Ypresian).
Younger strata (the Buchak Formation) contain already palunofacies that could be interpreted as indicative to deposition in more proximal setting than Kanev Formation. It contains higher ratio of terrestrial plant remains, whereas dinoflagellate cysts are dominated by near-shore species Homotryblium tenuispinosum.
   Bartonian strata (the Kiev Formation) yieldrich and diversified dinoflagellate cysts assemblages, which are indicative for marine environments. Taxonomical richness and occurrence of an oceanic genus Impagidinium suggests offshore sedimentary setting during Bartonian. A gradual sea withdraw can be interpreted as Priabonian: diversified assemblages in basal part of the Obuhov Formation, become relatively impoverished in the upper part of this unit where representatives of the genus Deflandrea and Prasinophyta algae (Pterospermella, Tasmanites) occur. Land-influences are markedly evident in Lower Oligocene Miezhigor Formation: palynofacies is dominated by sporomorphs and land plant tissue remains. Moreover, freshwater algae also frequently occurs.
   Preliminary comparison of our data with palynology of coeval strata from Polish part of epicontinental sea and Carpathian basins suggests that these basins were presumably connected during the Middle and Late Eocene. This is based on general taxonomical composition similarity of our assemblages to those known from Middle and Upper Eocene strata of the Flysch Carpathians (e.g., the Variegated Shale, the Hieroglyphic Beds). Throughout Early Oligocene, however, epicontinental basins were rather separated from Carpathian ones. Dinoflagellate cysts from the Miezhigor Formation are relatively diversified, whereas the ones from coeval Menilite facies of the Carpathian basins are almost absent.
   Acknowledgements: This research was supported by the Polish Ministry of Science and Higher Education research grant N N307 107035.