The Kara/Ust-Kara twin impact structure; A large-scale impact event in the Late Cretaceous

The Kara impact structure, on the Kara Sea coast of Russia, consists of two adjacent impact craters, the Kara and the Ust-Kara craters. The Kara crater is located on land and has a pre-erosion diameter of about 65 km, whereas the Ust-Kara crater is mostly submarine and has only limited onshore exposure. The diameter of the Ust-Kara crater was earlier suggested to be about 25 km, but recent morphological studies indicate a diameter >70 km. This is not incompatible with Seasat and Geosat data. It has been suggested that the Kara impact event may be associated with the K/T boundary event. Previously reported K-Ar ages showed wide margins of uncertainty and clustered around 60 Ma, while more recent K-Ar determinations seemed to support an association with the K/T boundary. Our own analyses of several 40Ar-39Ar age spectra, however, indicate an age of >70 Ma for the Kara impact event, perhaps close to the age of the Campanian-Maastrichtian boundary. Even if there is no association with the K/T boundary event, a double impact leading to craters of approximately 65 and 80 km diameter must have been an important geologic event with possible global significance. The record of this large-scale impact event may have been preserved in deep-sea sediment cores.