Unveiling the nature of glassy impact spherules by analyzing pristine Chicxulub spherules from Gorgonilla Island

The Chicxulub impact triggered a massive extinction event marked by the Cretaceous-Paleogene boundary (K-Pg ∼66Ma), ejecting vast amounts of dust, molten, and vaporized materials. While impact spherules are interpreted as products of impactor and target lithologies, their precise composition and distribution remain insufficiently constrained. Although previous studies restrict impactor contamination to the condensed spherules from the fireball layer and the K-Pg boundary clay, here we show asteroid contribution to the composition of large spherules from the base of the K-Pg bed. Despite those spherules displaying an apparent immiscible bimodal composition of yellow (Ca-rich) and black (Si-rich) glasses, novel nano-resolution analyses demonstrate enrichment of elements derived from the impactor. By analyzing pristine spherules from the normally-graded sequence of Gorgonilla Island K-Pg site, our results show the presence of metals and platinum group elements (PGEs) in glasses and vesicles within large molten spherules. Furthermore, needle-like and cubic-shaped nanostructures co-localizing Pt, Co, Ni, and Pb, and Cu, Os, and Zn, may represent the first evidence of quasicrystals (quasi-periodic solids, not found in terrestrial rocks, with symmetries forbidden for crystals) in Chicxulub-derived deposits. Those nanostructures challenge the definitions of microtektites and microkrystites, suggesting these classifications are misleading. We recommend abandoning such terminology, preserving the generic term "impact spherules," irrespective of composition, morphology, or size. Our findings contribute to refining the classification and interpretation of impact spherules, advancing our understanding of the processes underlying hypervelocity impacts. Moreover, these insights may hold relevance not only for terrestrial impacts but also for analogous extraterrestrial contexts.