Rich and heterogenous fossil ostracod fauna in the Ordovician sediment intrusions at Osmussaar Island, Estonia, reveals an ancient impact event

Carbonate quartz-sandstone intrusions, penetrating the brecciated limestone of the Volkhov and Kunda Stages (Dapingian–early Darriwilian) in the northwestern part of Estonia have been posing questions about their genesis for more than a century. The intrusions contain a rich, diverse and well preserved ostracod fauna, which is extremely heterogeneous and shows associations of species from different habitats or facies zones. The ostracod fauna in the intrusions refers to rapid horizontal mixing and displacement of a thick layer of bottom sediments, possibly resulting from a yet unknown impact event.