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Published March 2023 | public
Journal Article

New age constraints support a K/Pg boundary interval on Vega Island, Antarctica: Implications for latest Cretaceous vertebrates and paleoenvironments


A second K/Pg boundary interval in the northern sector of the Antarctic Peninsula on Vega Island has been proposed, yet current temporal resolution of these strata prohibits direct testing of this hypothesis. To not only test for the existence of a K/Pg boundary on Vega Island but also provide increased age resolution for the associated vertebrate fauna (e.g., marine reptiles, non-avian dinosaurs, and avian dinosaurs), the Vega Island succession was intensively re-sampled. Stratigraphic investigation of the Cape Lamb Member of the Snow Hill Island Formation, and in particular, the overlying Sandwich Bluff Member of the López de Bertodano Formation, was conducted using biostratigraphy, strontium isotope stratigraphy, magnetostratigraphy, and detrital zircon geochronology. These data indicate a Late Campanian–early Maastrichtian age for the Cape Lamb Member and present three possible correlations to the global polarity time scale (GPTS) for the overlying Sandwich Bluff Member. The most plausible correlation, which is consistent with biostratigraphy, detrital zircon geochronology, sequence stratigraphy, and all but one of the Sr-isotope ages, correlates the base of the section to C31N and the top of the section with C29N, which indicates that the K/Pg boundary passes through the top of the unit. A second, less plausible option conflicts with the biostratigraphy and depends on a series of poorly defined magnetic reversals in the upper part of the stratigraphy that also correlates the section between C31N and C29R and again indicates an inclusive K/Pg boundary interval. The least likely correlation, which depends on favoring only a single Srisotope age at the top of the section over biostratigraphy, correlates the section between C31N and C30N and is inconsistent with an included K/Pg boundary interval. Although our preferred correlation is well supported, we failed to identify an Ir-anomaly, spherules/impact ejecta, or other direct evidence typically used to define the precise position of a K/Pg boundary on Vega Island. This study does, however, confirm that Vegavis, from the base of the Sandwich Bluff Member, is the oldest (69.2–68.4 Ma) phylogenetically placed representative of the avian crown clade, and that marine vertebrates and non-avian dinosaurs persisted in Antarctica up to the terminal Cretaceous.

Additional Information

© 2023 Geological Society of America. We are grateful to editor Brad Singer, associate editor Xixi Zhao, and two anonymous reviewers, who provided exceptionally insightful feedback. We thank the crews of the U.S. Antarctic Program research vessels R/V Lawrence M. Gould and R/V Nathaniel B. Palmer for field and other logistical assistance during the 2011 and 2016 field seasons. Harry Gardner and Jodie Kilpatrick provided substantial assistance with initial testing of Sr-isotope techniques and diagenesis filtering on samples from Vega Island. C. Thissen, K. Hillbun, S. Schoepfer, S. Alesandrini, P. Ward, D. Smith, J. Meng, E. Gorscak, J. Sertich, C. Torres, A. West, R.D.E. MacPhee, and the Air Center Helicopter staff and pilots are thanked for field assistance during the 2011 and 2016 field seasons. Field work and stratigraphic analysis benefited from discussions with D. Barbeau (University of South Carolina, Columbia, South Carolina). This research was supported by National Science Foundation grants ANT-0636639 and ANT-1142052 to Ross D.E. MacPhee, ANT-1142129 to M.C. Lamanna, ANT-1142104 to P.M. O'Connor, ANT-1141820 to J.A. Clarke, and ANT-1341729 to J.L. Kirschvink. Sr-isotope, palynological, and U-Pb detrital zircon data are available in the Supplemental Material. Rock magnetic data are available on Zenodo (https://doi.org/10.5281/zenodo.6301037), and paleomagnetic data are available in the MagIC database (https://www.earthref.org/MagIC/doi/10.1130/B36422.1).

Additional details

August 22, 2023
October 23, 2023