none 10.1144/jgs2020-034 Geological Society of London Geological Society of London 1881 117520043 44798 2024111903342300533 10.1144 2024-11-19T14:11:30Z 2020-07-01T15:52:27Z 12 Journal of the Geological Society JGS 0016-7649 2041-479X 11 02 2020 11 2020 177 6 Gavin G. Kenny Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden https://orcid.org/0000-0001-8683-3860 Irmeli Mänttäri Radiation and Nuclear Safety Authority, Laippatie 4, Box 14, FI-00811 Helsinki, Finland Martin Schmieder Lunar and Planetary Institute – Universities Space Research Association, Houston, TX 77058, USA Hochschule Neu-Ulm, Neu-Ulm University of Applied Sciences, D-89231 Neu-Ulm, Germany https://orcid.org/0000-0002-1458-5148 Martin J. Whitehouse Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden https://orcid.org/0000-0003-2227-577X Alexander A. Nemchin Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden School of Earth and Planetary Sciences, Curtin University, Perth, WA 6845, Australia Jeremy J. Bellucci Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden Renaud E. Merle Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden https://orcid.org/0000-0001-9018-6862 We report a new age for the Sääksjärvi impact structure, Finland, a 6 km diameter feature that formed in crystalline rocks of the Precambrian Baltic Shield. Two previous studies reported 40 Ar/ 39 Ar data for Sääksjärvi and suggested conflicting formation ages of ≤330 Ma or c. 560 Ma. The former age represents a possible complication for models which indicate that the region was covered by sediments of the Caledonian foreland basin throughout much of the Phanerozoic. We conducted a study combining imaging, microstructural analysis and U–Pb dating of shocked zircon from Sääksjärvi. The U–Pb dataset indicates a c. 600 Ma impact into predominantly c. 1850 Ma target rocks. A concordia age of 608 ± 8 Ma (2 σ ) confirms Sääksjärvi as the first known Ediacaran impact structure in the Baltic Shield and only the second worldwide. Our data indicate that the Sääksjärvi impact structure formed in exposed crystalline basement rocks of the Baltic Shield prior to the development of the Caledonian foreland basin. Given that most impact structures on Earth are relatively small features, radiometric dating of small impact structures in crystalline basement may place boundaries on the timing and spatial extent of palaeobasins that might otherwise be difficult to constrain. Supplementary material: Additional imaging and microstructural analysis of zircon, additional concordia plots, and U–Pb data tables are available at https://doi.org/10.6084/m9.figshare.c.5043462 07 30 2020 11 2020 1231 1243 10.1144/jgs2020-034 1 10.1144/crossmark-policy www.lyellcollection.org true 2020-02-20 2020-06-15 2020-06-29 2020-07-30 H2020 Marie Skłodowska-Curie Actions http://dx.doi.org/10.13039/100010665 792030 https://doi.org/10.15223/policy-002 10.1144/jgs2020-034 https://www.lyellcollection.org/doi/10.1144/jgs2020-034 https://www.lyellcollection.org/doi/pdf/10.1144/jgs2020-034 https://geoscienceworld.org/jgs/article-lookup?doi=10.1144/jgs2020-034 10.1016/j.chemgeo.2004.01.003 Bottomley R.J. York D. and Grieve R.A.F. 1990. 40 Ar– 39 Ar dating of impact craters. Proceedings of the Lunar and Planetary Science Conference 20 421–431. Buchner E. Moilanen J. Öhman T. and Schmieder M. 2009. 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