66±1 Ma single zircon U-Pb date confirms the location of the non-marine K-Pg boundary in the Amur/Heilongjiang River area, (Russia, China)

The location of the K-Pg boundary in the non-marine Upper Cretaceous to Lower Paleogene successions in the Amur/Heilonjiang River area along the Russian-Chinese border is of considerable interest for studies of floral extinctions across this boundary. So far, there has been little agreement between the locations of that boundary based on paleontological evidence as compared to evidence based on radiometric dating. Single zircon LA-ICP-MS dating of a thin tuff bed of the Wuyun Formation (Heilongjiang area, China) located above the assumed boundary layer gave a published age of 64.1±0.7 Ma. In the present study, we report a 66±1 Ma U-Pb age average obtained by LA-ICPMS dating of single igneous zircons from a tuff bed located below the assumed boundary layer, in the uppermost part of the Middle Tsagayan Subformation (Ploskaya Mt. section, Russia). In combination, these data confirm the paleontological evidence. The new data likewise shows that previous attempts to date the tuffs by zircon dating suffered from the presence of old, inherited zircons/zircon cores.