A Greenland ice-core study by Michail Petaev, Shichun Huang, Stein Jacobsen, and Alan Zindler found almost no iridium but detected a pronounced platinum spike beginning exactly 12,900 years ago.
Notes on verification
Confirmed by the original 2013 PNAS paper (Petaev et al.) and corroborated by independent secondary sources. Minor nuance: a later review notes a very weak extended iridium signal was detected, consistent with 'almost no iridium' rather than absolute zero.
Sources
- Did a Comet Really Kill the Mammoths 12,900 Years Ago? (nationalgeographic.com)
- https://www.pnas.org/doi/10.1073/pnas.1303924110 (pnas.org)
- https://pubmed.ncbi.nlm.nih.gov/23878232/ (pubmed.ncbi.nlm.nih.gov)
- https://www.nature.com/articles/srep44031 (nature.com)