POSSIBLE EJECTA FROM THE BOLTYSH IMPACT EVENT (UKRAINE) IN ITALY

Boltysh is an about 24-km-diameter complex impact structure, which is situated in the central part of the Ukrainian Shield. The crater is surrounded by an ejecta blanket represented by a polymict breccia layer extending over an area of -6500 km². The ejecta blanket outside the crater is extensively eroded and varies in thickness from tens of meters at a distance of about 2-3 crater radii to 1-4 meters at 4-5 crater radii from the center of the structure. The - so far - farthest recorded distance of the ejecta is ca. 66 km or 5.5 crater radii to the W-N-W of the Boltysh structure. Boltysh was, for quite some time, thought to be coeval with the Chicxulub impact event and the K-Pg boundary mass extinction, but more recently was found to be ca. 0.6 Ma younger than the K-Pg age; however, this age agrees with the astrochronological age of the so-called ALE ash layer in the Danian pelagic succession of the Scaglia Rossa formation in the Umbria-Marche sequence, Italy. This coincidence raises the question if there is a possible connection between the Boltysh impact event and the ALE ash layer.

We used trace element and isotope analyses to study the composition of samples of this layer from three Italian sections, as well as impactites from the Boltysh structure, to search for a meteoritic component. Meteoritic signatures were found in at least two of the Boltysh impactites, with near-chondritic Os-isotopic ratios of 0.13 and minor Ir abundance anomalies (0.16-0.36 ppb Ir). In agreement some earlier studies, Boltysh impactites seem to have a rather minor meteoritic component. Potential meteoritic signatures, based on siderophile element abundances and Os isotopic signatures, have also been identified within the ALE ash layers or immediately adjacent layers, indicating the possible deposition of impact ejecta within/as the ALE ash in the Danian pelagic succession in Italy. Even though the age dating indicates that the ALE ash deposition coincides with the Boltysh impact event, and a potential meteoritic component has been identified in the ALE ash layer, it is not yet possible to unambiguously confirm that Boltysh is the source of the meteoritic component detected here – but it is a likely conclusion.