Dating and palaeoenvironmental reconstruction of the sediments around the Miocene/Pliocene boundary in Yermak Plateau ODP Hole 911A using marine palynology

The late Neogene evolution of the Arctic to Subarctic region is poorly understood due to few available records and poor age control. At the margin of the Arctic Ocean, Yermak Plateau Ocean Drilling Program (ODP) Hole 911A is strategically located for establishing a stratigraphic framework for the Arctic. Here we present dinoflagellate cyst and acritarch data from 24 stratigraphic levels in the lower part (474.26–505.64metresbelow the seafloor of ODP Hole 911A. The marine palynomorphs indicate a latest Miocene to earliest Pliocene age (between 5.8 and 5.0Ma) for the base of the hole based on the co-occurrence of the dinoflagellate cyst Barssidinium evangelineae and acritarch Lavradosphaera crista. Our age estimate can possibly be further refined to 5.0–5.33Ma based on the presence of Achomosphaera andalousiensis suttonensis, which apparently has a range restricted to the Pliocene. An age close to the Miocene/Pliocene boundary agrees with the planktonic foraminifer data. Together with recently available magnetostratigraphic data, the base of the hole is likely to be placed at ~5.2Ma. This new chronostratigraphy is a first step towards a better understanding of the late Neogene palaeoenvironment for the Yermak Plateau and also for the wider Arctic to the Subarctic region.The terrestrial and fresh water palynomorphs were most likely redistributed and/or displaced from the shelf towards deeper parts of the basin during contourite deposition under the influence of the West Spitsbergen Current. The in situ marine dinoflagellate cyst assemblage contains a mixture of cool water and thermophilic taxa, indicating sea-ice free, cool-temperate, and warmer than present conditions at the Yermak Plateau. Rivers were likely the source for the freshwater influence.Warmer than present conditions may have occurred due to northward warm water transport via the West Spitsbergen Current, but also the absence of sea-ice and consequent lower albedo could have played a role.