Late Eocene (Priabonian) dinoflagellate cysts from Primorsky Quarry, southeast Baltic coast, Kaliningrad Oblast, Russia

Abstract

Forty-seven rock samples from the stratotypes of upper Paleogene formations - Prussian, Palvé and Kurshskaya formations – are collected from the biggest amber deposit worldwide (Primorsky quarry, Kaliningrad oblast, SE Baltic coast), and have been palynologically analyzed. The presence of age-diagnostic dinoflagellate species has allowed us to refine and update the previously questionable age of regional lithostratigraphic units. Based on the presence of Rhombodinium perforatum, the “Upper Wild Earth” and “Upper Blue Earth” members of the Prussian Formation correspond to the early Priabonian (Late Eocene) Rhombodinium perforatum Zone. The overlying “Upper Quicksand” and “White Wall” members of the Prussian Formation contain the key-species Thalassiphora reticulata, and are correlated with the late Priabonian T. reticulata Zone. The overlying Palvé Fm (“Green Wall”), comprises a dinoflagellate cyst assemblage very close to that recorded from the Prussian Formation, and also corresponds to the T. reticulata Zone, late Priabonian. The lower part of the Kurshskaya Formation – “Chocolate clays” and lower “Brown sands” members, contain an impoverished dinoflagellate cyst assemblages as a result of significant environmental changes. However, the common presence of Areosphaeridium diktyoplokum and Glaphyrocysta semitecta, along with an absence of early Oligocene key-species Wetzeliella gochtii or Chiropteridium galea, and pollen key-species Boehlensipollis hohli or Aglaoreidia cyclops, suggest the lower Kurshskaya Formation can be correlated with the latest Eocene, and very close to the Eocene/Oligocene boundary. Based on the revised stratigraphic ages presented here, we suggest an important regional marine transgression occurred during the Priabonian, which allowed the direct marine connection between the NW European Basin and Peri-Tethys via the Polish-Luthuanian Seaway. This was then followed by a regression at the end of Priabonian that culminated in a transition to continental sedimentation in the early Rupelian. A new dinoflagellate cyst species Oligokolpoma balticus sp. nov. is formally described.