The Paleocene of Antarctica: dinoflagellate cyst biostratigraphy, chronostratigraphy and implications for the palaeo-Pacific margin of Gondwana

The Paleocene (66–56 Ma) was a critical time interval for understanding recovery from mass extinction in high palaeolatitudes when global climate was warmer than today. A unique sedimentary succession from Seymour Island (Antarctic Peninsula) provides key reference material from this important phase of the early Cenozoic. Dinoflagellate cyst data from a 376 m thick stratigraphical section, including the Cretaceous–Paleogene boundary, is correlated with biozones from New Zealand, the East Tasman Plateau and southeastern Australia. A detailed age model is suggested for the López de Bertodano (LDBF) and Sobral (SF) formations based on dinoflagellate cyst biostratigraphy and U-Pb dating of zircons, supported by correlated magnetostratigraphy and strontium isotope values from macrofossils. The top of the LDBF is confirmed as latest Maastrichtian to earliest Danian (~ 66.2–65.65 Ma) in age. The overlying SF is mostly Danian in age, with an inferred hiatus near the top overlain by sediments dated as? late Thanetian. Rare Apectodinium homomorphum first appear in the uppermost SF; the first in situ record from Antarctica. The distribution of marine and terrestrial fossils from uppermost Cretaceous to Eocene sediments in Patagonia, Antarctica, New Zealand and Australia required both sea and land connections between these fragments of Gondwana. Fossil evidence and reconstructions of Antarctic palaeogeography and palaeotopography reveals evidence for persistent embayments in the proto-Weddell and Ross Sea regions at this time. We conclude that a coastal dispersal route along the palaeo-Pacific margin of Gondwana could explain the fossil distribution without requiring a transAntarctic strait or closely spaced archipelago. A region in the West to East Antarctic boundary zone, elevated until the early Paleogene, perhaps acted as a site for high elevation ice caps. This supports fossil, geochemical and sedimentological evidence for cold climate intervals and significant sea level falls during the Maastrichtian and Paleocene.

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