Paleoclimatology and Paleoecology across the Eocene/Oligocene boundary, Thrace Basin, Northeast Aegean Sea, Greece

The detailed biostratigraphic and ichnological analysis of the Upper Eocene/Lower Oligocene forearc sedimentary sequence in the southern Greek part of the Thrace Basin on Lemnos Island reveals a relationship between eco-sedimentary factors and the base-level dynamics influencing calcareous nannofossils and trace fossil assemblages. The lower part of the ~ 350 m thick succession was deposited in a sand-rich submarine fan system and upper part in a shelf environment. It contains nannofossil assemblages and distributions typical of the NP19–NP21 biozones. The Eocene/Oligocene (E/O) boundary (top of NP20 biozone) is clearly distinguished within the upper parts of the turbidite system where a decrease in water temperature, salinity, nutrient supply and oxygenation level is also revealed. Additionally, 19 ichnospecies, mostly graphoglyptids typical of deep-sea fan deposits, have been distinguished. The trace fossil diversity and abundance decrease upward reflecting the impact of the changing depositional environments from basin floor fans, to slope systems and then shelfal environments. The regional basin-fill history, rather than global climatic changes, was probably the fundamental controlling factor on the distribution of graphoglyptids and other trace fossils across the E/O boundary.