11:30 AM - 11:45 AM
[SGC46-04] Platinum group elements and Re-Os isotopes in the K-Pg transition of the Chicxulub peak-ring rocks
Keywords:Platinum group elements, Re-Os isotopes, Cretaceous-Paleogene boundary, Chicxulub crater
Platinum group element (PGE) concentrations and 187Os/188Os compositions show systematic variations across the transitional layer. The upper part (616.59–616.63 mbsf) is characterized by about one order of magnitude higher Os, Ir, and Ru contents compared to the average continental crust abundances, but much lower than for the typical Ir-enriched Cretaceous–Paleogene boundary distal sites (e.g., Gubbio and Caravaca: Alvarez et al., 1980; Smit and Hertogen, 1980). Relatively flat CI chondrite–normalized PGE patterns are observed in the upper part of the layer. Meanwhile, the PGE concentrations in the lower part of the transitional layer (617.315–617.34 mbsf) are almost equivalent to those of upper continental crust showing pronounced step CI chondrite-normalized PGE patterns (0.8–1.2 × 10-4 for Ir, and 1.2–2.7 × 10-3 for Pt and Pd). 187Os/188Os and Re/Os ratios in the transitional layer gradually decrease from 0.33 to 0.25 and 35.45 to 1.14, respectively, from bottom to top. These results suggest that the projectile component, with chondritic composition, is enriched in the uppermost part of the transitional layer just below carbonate rocks that are early Paleogene in age, but could be distributed over a thicker interval than for the Ir-enriched sites. Further detailed studies of PGE and 187Os/188Os compositions through the stratigraphic sequence will reveal the distribution and dilution effect of the projectile component.