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THE KÄRDLA, TVÄREN, AND LOCKNE CRATERS – POSSIBLE EVIDENCES OF AN ORDOVICIAN ASTEROID SWARM

1992; Estonian Academy Publishers; Volume: 41; Issue: 2 Linguagem: Inglês

10.3176/geol.1992.2.01

1736-7913

Tom Flodén, Maurits Lindström, V. Puura, Kalle Suuroja,

Comparisons of crater infill of the Middle Ordovician (Idavere) impact craters of Kirdla (NW Estonia), Tvidren (SE central Sweden), and Lockne (NW central Swe- den) have shed new light on asteroid impact events in epicontinental seas, calling also for new diversified terminology.The three craters are interpreted as having resulted from an asteroid swarm that hit Baltica in the early Idavere time.The infilling of the 4 km wide Kéirdla crater is used as type section.The Kairdla asteroid hit an area of relatively shallow water with a 140 m thick Cambro-Ordovician sequence covering the Precambrian crystalline basement.During an initial dry phase of the cratering event, crystalline-dominated autochthonous and subautochthonous breccias were