Geochemical investigation of impactites from the Boltysh impact structure and possible relationship to early Danian sediments from the Umbria–Marche Basin, Italy

Abstract Within the Danian Scaglia Rossa Formation appears a regionally correlatable horizon cutting across multiple sections and outcrops within the Umbria–Marche Basin of NE Italy, where it is intercalated with uniform pelagic carbonate successions. This horizon is called “ALE layer” and has tentatively been interpreted as a fine‐grained volcanic ash. A key motivation for this study is the striking agreement between the ages of the ALE bed (65.440 ± 0.005 Ma) and the Boltysh impact event (65.39 ± 0.14/0.16 Ma), raising the possibility that the ALE layer preserves a distal Boltysh ejecta component transported over ~1600 km, while its bulk may reflect a longer duration volcanosedimentary depositional interval. To test this hypothesis, we combine impact‐scaling considerations with highly siderophile element (HSE) and Cr‐Os isotope data for Boltysh impactites and geochemical and Os isotopic analyses of the ALE horizon. Chromium isotope compositions of the Boltysh impactites (as low as ε 54 Cr = −0.31) may indicate an extraterrestrial contribution; however, their interpretation remains ambiguous. If interpreted as such, implausibly high IIIAB iron meteoritic admixtures would be required. By contrast, HSE abundances and 187 Os/ 188 Os systematics indicate clearly resolvable meteoritic components of up to 1 wt% CI‐equivalent, forming coherent crust–chondrite mixing arrays. The ALE bed, though dominated by volcanosedimentary material, consistently shows Os–Ir–Pt–Pd enrichments far above the pelagic background, requiring up to ~0.8 wt% CI meteoritic input if interpreted in terms of an impact event horizon. Unradiogenic 187 Os/ 188 Os excursions occur primarily within the ALE layer, but in some cases extend into adjacent pelagic carbonate layers stratigraphically above and below the ALE layer. These unradiogenic 187 Os/ 188 Os excursions define chondritic‐trending trajectories that mirror those in the Boltysh samples and are interpreted as diffusion‐modified expressions of an originally ALE‐centered meteoritic Os input. Taken together, the temporal coincidence between the Boltysh impact event and the ALE layer, impact‐scaling relationships, and HSE‐ and Os‐isotopic signatures favors the interpretation that the ALE layer preserves a distal equivalent of the Boltysh impact ejecta diluted within a volcanosedimentary depositional system that was subsequently modified by diagenetic processes.