High Arctic late Paleocene and early Eocene dinoflagellate cysts

Abstract. Palynomorphs, notably sporomorphs and organic-walled dinoflagellate cysts, or “dinocysts”, are the only abundant microfossils consistently present in the sole available central Arctic upper Paleocene to lower Eocene sedimentary succession recovered at the central Lomonosov Ridge by the Integrated Ocean Drilling Program (IODP) Expedition 302 (or the Arctic Coring Expedition, ACEX) in 2004, close to the North Pole. While the analysis and interpretation of a part of these assemblages have so far guided many major stratigraphic, climatological, and paleoenvironmental findings from ACEX, intrinsic details, notably of the dinocyst taxa and assemblages, have not yet been addressed. Here, we present new ACEX dinocyst data for the interval spanning the latest Paleocene to the earliest Eocene (∼56.5–53.8 Ma; cores 32X–27X) and integrate these with previous results. We develop a pragmatic taxonomic framework, document critical biostratigraphic events, and propose two new genera (Guersteinia and Sangiorgia) and seven new species (Batiacasphaera obohikuenobeae, Chaenosphaerula sliwinskae, Heterolaucacysta pramparoae, Pyxidinopsis iakovlevae, Sangiorgia pospelovae, Sangiorgia marretiae, and Spiniferella crouchiae). In addition, we interpret trends and aberrations in dinocyst assemblages in terms of variability in regional temperature, hydrology, and tectonism across the long-term and the Paleocene–Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2) global warming phases.