Early and middle Eocene dinoflagellate cysts from the Aktulagay section, Kazakhstan
A mid neritic-upper bathyal Ypresian section at Aktulagay, western Kazakhstan, has been analyzed palynologically. A number of key dinoflagellate cyst events are directly calibrated with published calcareous nannofossil data from the same section. The events are used to identify eight dinoflagellate cyst zones from a recently established zonation, used elsewhere in the eastern Peri-Tethys, and to calibrate these zones with the standard nannofossil zonation (NP zones). The events include the lowermost occurrences of Deflandrea oebisfeldensis (∼1%), Dracodinium simile, Eatonicysta ursulae, Dracodinium varielongitudum, Charlesdowniea coleothrypta, Ochetodinium romanum, Charlesdowniea columna, Samlandia chlamydophora, Areosphaeridium diktyoplokum, and Wetzeliella eocaenica. An important regional unconformity separates the Ypresian section from overlying non-calcareous strata with the age-diagnostic species Enneadocysta arcuata, Wetzeliella ovalis, Wilsonidium echinosuturatum, and Rhombodinium draco, indicating the Rhombodinium draco Zone of latest Lutetian–Bartonian age. Based on fluctuations of ecological groups of dinoflagellate cysts, a series of different depositional environments are interpreted and related to the existing sequence stratigraphic model of the section. In most cases dinoflagellate cyst agree with, or supplement, calcareous micro- and nannofossil indications, and support the sequence stratigraphic model. Impagidinium wardii sp. nov. is atypical for the otherwise oceanic genus as it bloomed in a mid-neritic environment. The first cooling at the end of the Early Eocene Climatic Optimum (EECO) is suggested to have caused a strong acme of Eatonicysta ursulae and distinct lowering of the sea level in the NP13 zone. Four new species are formally described: Cribroperidinium cavagnettiae sp. nov., Dracodinium robertknoxii sp. nov., Impagidinium wardii sp. nov., and Samlandia chriskingii sp. nov. The Aktulagay Formation of King et al. (2013) is renamed the Kulsary Formation.
