Early Oligocene palaeoenvironment and palaeoclimate of the eastern periphery of the North Sea based on high-resolution palynological studies of the Grabówka PIG-1 borehole, northern Poland

High-resolution palynological studies of the lower Oligocene strata from the Grabówka PIG-1 borehole from the eastern peripheries of the North Sea (Polish Gulf) revealed the presence of 165 fossil-species of sporomorphs (pollen grains and spores), numerous marine palynomorphs (e.g. dinoflagellate cysts), freshwater and brackish algae, plus fungal remains (including microsclerotia of dark septate endophytes inhabiting roots of plants). The composition of the palynological assemblage, including the fossil-species Boehlensipollis hohli Krutzsch and Aglaoreidia cyclops Erdtman, confirms the early Oligocene age of the strata. The presence of numerous dinoflagellate cysts throughout the Grabówka PIG-1 succession clearly indicates its deposition in a shallow marine, near-shore environment. The results of the spore-pollen analysis indicate the presence of lush vegetation with numerous thermophilous elements (including members of the pantropical families Meliaceae Jussieu and Sapotaceae Jussieu as well as the subtropical-tropical families Arecaceae Berchtold & J.Presl, Schizaeaceae Kaulfman, ­Cyatheaceae Kaulfman and/or Gleicheniaceae C.Presl) in the neighbouring land area. Mixed mesophytic forests, wetland (swamp or riparian) forests, shrub bogs, and freshwater/marsh vegetation dominated there. The climate was subtropical and humid. The entire palynological succession corresponds to the 5th Czempiń group of lignite seams, correlated with the 5th Lusatian seam in south-eastern Germany, which is an important correlation horizon for the lower Oligocene in Central Europe. The results provide new insights into the vegetation and palaeoclimate changes in mid-latitudes during the early Oligocene greenhouse/icehouse transition.