Dataset. Santa Barbara Basin marine sediments (ODP Site 893A) provide an ultra-high-resolution stratigraphic record across the enigmatic Younger Dryas (YD) climatic episode (12.8–11.7 ka BP). Numerous studies have proposed a cosmic impact as the trigger of abrupt cooling and near-simultaneous climatic, biotic, and human changes at the YD onset (~12,800 cal BP). However, the Younger Dryas Boundary (YDB) impact hypothesis remains debated. High-resolution electron-microscopic and single-particle mass-spectrometric analyses (SEM, EDS, and SP-ICP-TOF-MS) reveal distinct abundance peaks in metallic flakes, SiO₂ spherules, pyrite framboids, and framboids coated with vesicular silicate meltglass confined to the YDB layer. Nanoparticle analyses (45 elements) reveal multi-elemental species enriched in platinum-group elements (PGEs), Fe-Ni alloys, and refractory phases, with particle concentrations ≈3× above background and mass concentrations at ≈4×. In contrast, the mean mass per nanoparticle declines ≈70 %. PGE/Fe ratios are 5–10× crustal values, and Fe/Ni–Fe/Cr relationships match cometary and meteoritic dust. Principal-component analyses define four sequential nanoparticle populations: (i) a pre-YDB terrestrial assemblage; (ii) a YDB population enriched in PGEs, Ni-Fe alloys, and fine-grained particles consistent with an impact-caused atmospheric dust storm (~4–6 yr); (iii) a post-YDB fallout layer (~16–22 yr); and (iv) a return to background conditions. The coincidence of sharp microparticle peaks with PGE-rich nanoparticles indicates rapid condensation and deposition of impact-derived material followed by decadal atmospheric fallout. Alternative volcanic, solar-plasma, or diagenetic processes cannot account for these coupled morphological and geochemical signatures, and the weight of evidence favors an extraterrestrial impact origin.