The Age and Depositional Settings of the Upper Paleogene–Lower Neogene Kurshskaya Formation in its Stratotype Section (Kaliningrad Oblast) based on Palynological Data

Abstract—

The results of the palynological study of the Kurshskaya Formation stratotype (Primorsky quarry, Kaliningrad Oblast) are presented. The lower part of the Kurshskaya Formation (Member of “chocolate” clays) contains an assemblage of latest Eocene dinoflagellate cysts Areosphaeridium diktyoplokum, Glaphyrocysta semitecta, and Cordosphaeridium funiculatum. The formation is characterized by four spore-pollen assemblages: (1) latest Eocene Pinuspollenites–Inaperturopollenites–Sciadopityspollenites assemblage in the “chocolate” clays and in the lower part of brown sands; (2) early Oligocene Sequoiapollenites–Betulaepollenites betuloides assemblage in the lower part of the brown sands member; (3) early Oligocene Boehlensipollis hohli–Carpinipites carpinoides in the middle part of brown sands member; (4) late Oligocene–early Miocene Alnipollenites–Corylopollis assemblage in the upper part of the brown sands of the Kurshskaya Formation. In total, the Kurshskaya Formation is terminal Eocene–early Miocene in age. The lower part of the Zamland Formation, which overlies the Kurshskaya Formation, contains the presumably middle Miocene Pinuspollenites–Tricolporopollenites pseudocingulum–T. euphorii assemblage. Based on the obtained palynological data, the depositional settings at the end of the Eocene–Oligocene–early Miocene in the South Baltic region are reconstructed. The regression of the marine basin began as early as the end of the Priabonian, the climate was still quite warm and humid, close to subtropical. Mesophytic mixed coniferous-broad-leaved forests grew along the shores of the strait, lowlands were occupied by marsh vegetation. Cooling at the Eocene/Oligocene boundary resulted in the appearance of hemlock in plant communities and increase in the proportion of catkins (alder, birch, hornbeam). Presumably, in the late Oligocene–early Miocene, the proportion of small-leaved trees, especially alder and hazel, sharply increased in mesophytic forests, while the number of pine trees decreased. Wetter and warmer climatic conditions are assumed for the early Miocene: this time is characterized by an increase in the number of walnut, cypress, and Cyrillaceae. In the middle Miocene, the climate was still quite warm, but drier, and such moisture-loving species as Podocarpus, spruce, Glyptostrobus, and swamp cypress disappeared from plant communities.