Chitinozoan dating of Ordovician impact events in Sweden and Estonia. A preliminary note

Four impact craters of Ordovician age are known from Sweden and Estonia. Chitinozoans from impact and post-impact sediments in these craters have been investigated. Three craters (Kärdla, Tvären and Lockne) were created at different occasions in the earliest Caradoc, and one crater (Granby) probably in late Arenig.