THE NUMERICAL AGE OF THE DEVONIAN CARBONIFEROUS BOUNDARY

The SHRIMP ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the Hasselbachtal auxiliary global stratotype section through the Devonian-Carboniferous boundary in Germany, and a tuff located at a similar biostratigraphic level in Australia. Multiple replicate analyses have yielded indistinguishable ages, and indicate 353.2+/-4.0 Ma (2-sigma) as the age of the boundary. Obtaining an age for the boundary in the German reference section depended on the ability of SHRIMP to date a small sample and to target small areas of structurally complex zircons. Future refinements of the age of this boundary may depend on re-analysis of this uniquely placed bentonite. and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons.