Ample evidence exists for at least one major meteorite impact event at the time of the Cretaceous/Tertiary (K/T) boundary, and it is therefore important to establish if any recognized terrestrial impact craters are K/T in age. The Kara, USSR, impact structure consists of two adjacent large impact craters (a rare and interesting geologic phenomenon), and it has been suggested that this twin impact structure might be related to the K/T boundary event. However, newly determined 40Ar/39Ar and K-Ar ages presented here suggest that these structures are slightly older than 70 Ma, and may thus be too old for a 66 Ma K/T boundary event. Still, these two craters represent a substantial impact event that could have initiated regional, if not global, degradation of the biosphere. Their age suggests a possible relation with the Campanian/Maastrichtian boundary.

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