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Volume 15, issue 1 | Copyright
J. Micropalaeontol., 15, 21-35, 1996
https://doi.org/10.1144/jm.15.1.21
© Author(s) 1996. This work is distributed under
the Creative Commons Attribution 4.0 License.

  01 Apr 1996

01 Apr 1996

Precise chitinozoan dating of Ordovician impact events in Baltoscandia

Yngve Grahn1, Jaak Nõlvak2, and Florentin Paris3 Yngve Grahn et al.
  • 1Swedish Museum of Natural History, Department of Palaeozoology, Box 50007, S-10405 Stockholm, Sweden
  • 2Estonian Academy of Sciences, Institute of Geology, 7 Estonia Avenue, EE-0105 Tallinn, Estonia
  • 3Université de Rennes, Laboratoire de Paléontologie et Stratigraphie, URA 1364 du CNRS, Avenue du Général Leclerc, F-35042 Rennes Cedex, France

Abstract. The chitinozoan biostratigraphy of four Ordovician impact craters has been investigated. Three of these (Tvären, Kärdla and Lockne) contain complete sequences of early Caradoc age, while the Granby crater contains rocks of late Arenig age yielding two bentonitic horizons at their top. Chitinozoans, together with graptolites and other planktic organisms, were the first to invade the craters after the impact event. It has therefore been possible to date the impact events with a precision of less than one million years. An immigration of graptolites from Australia during the late Arenig corresponds to an immigration of chitinozoans from Gondwana at this time. Two stratigraphically important taxa, not previously described or discussed, Lagenochitina sp. A aff. capax and Laufeldochitina sp. A aff. striata are commented upon. Three species. Cyathochitina hunderumensis, Spinachitina tvaerenensis and Tartuchitina granbyensis, are described as new.

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