Microfossils in resin from the middle Eocene Buchanan Lake Formation, Napartulik, Axel Heiberg Island, Nunavut, Canada

AbstractDuring the warm middle Eocene (ca 45 Ma), the Napartulik area (also called ‘the Geodetic Hills’), Axel Heiberg Island, northern Canada (Nunavut), was vegetated with mixed broad-leaved deciduous angiosperm and evergreen conifer forests over extensive floodplain and forested wetland habitats. Massive organic rich sedimentary successions and encapsulated in-situ tree trunks suggest these forests were drowned by frequent flooding events. The sedimentary layers contain sub-fossil amber that was produced by representatives of the Pinaceae such as Pseudolarix. The amber offered an opportunity to investigate aerial plankton and thus the chance to discover microfossils, which could provide evidence of biotic interactions associated with, or the cause of, the forest die-offs. Fifty-four amber samples were subjected to a solvent treatment for microfossil extraction followed by light microscopy, resulting in the discovery of several hundred microfossils. Unexpectedly, one-quarter of the microfossils were diatoms, which may predominantly have lived on the tree bark. Fungal spores were rare, and the pollen grains found corroborated earlier findings in litter or coal. The records of fungal spores and arthropod remains were insignificant and could, therefore, not substantially have been contributing to the forest die-offs. More resin analyses from the complete sedimentary profile would be needed to get a clearer picture of putative forest pests and prevailing environmental conditionsKeywords: Arcticdiatomsforest die-offfungal sporespollenPaleogene swamp forest AcknowledgementsWe are indebted to Andreas Gminder (Goslar), Peter Karasch (Kirchl), Friedemann Klenke (Dresden), Lothar Krieglsteiner (Spraitbach), Julia Kruse (Bad Dürkheim), and Klaus Siepe (Velen) for assisting in the identification of fungal microfossils. Moreover, we are grateful to Reinhard Zetter (Vienna) for his advice in identifying pollen, and to Torsten Wappler (Darmstadt) for the taxonomic advice on arthropod remains. Thanks to the reviewers Przemysław Gedl (Polish Academy of Sciences) and Jennifer Galloway (Geological Survey of Canada) whose comments greatly improved the manuscript.Disclosure statementThe authors have no potential conflict of interest to declare.Additional informationFundingThere were many agencies that provided funding to Ben LePage over 13 field seasons (see previous publications), but the Polar Continental Shelf Project (PCSP) of Natural Resources Canada (formerly Energy, Mine, and Resources Canada) and staff need to be recognized for the field and logistical support they provided. The palynological investigations were privately funded.Notes on contributorsHans HalbwachsHans Halbwachs is a mycologist with a focus on fungal ecology. He has been an associate researcher at the Bavarian Forest National Park since 2008 and at Goethe University Frankfurt, Department of Conservation Biology since 2020. Since 2017, he has engaged in fungal paleontology and trait-based fungal ecology.Friðgeir GrímssonFriðgeir Grímsson is a paleobotanist and palynologist with a geological background. His focus is on pollen from Mesozoic to modern-day samples. He is a Senior Scientist at the Department of Botany and Biodiversity Research, University of Vienna, where he runs the electron microscopy laboratories, teaches various courses related to palynology and electron microscopy, and conducts palynological researchMarina PotapovaMarina Potapova is a curator of Diatom Herbarium at the Academy of Natural Sciences of Drexel University, Philadelphia, USA. Her research interests are in the taxonomy, ecology, and biogeography of inland and coastal diatoms.Martina DolezychMartina Dolezych is a paleontologist affiliated to the Senckenberg Natural History Collections Dresden in Germany. Her research focuses on the wood anatomy analyses of Cenozoic deposits. She is also interested in the stratigraphy and reconstruction of the palaeoenvironment.Ben LePageBen Lepage is trained as a biologist and geologist and has focused mainly on the taxonomy and paleoecology of Cenozoic high Arctic fossil forests with interest in the biogeographic and evolutionary histories of the Pinaceae and Cupressaceae (Taxodiaceae). He is currently a Distinguished Visiting Chair Professor in the Graduate Institute of Environmental Education at National Taiwan Normal University, Taipei, Taiwan. Prior to this, he spent around 20 years in the utility industry, leading project teams to develop innovative compliance and remediation strategies, and about eight years at the University of Pennsylvania, Philadelphia, PA.

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