Application of the fission-track dating method on sandstones. Depositional age and thermal history of the Paleogene Kishima Group, Nagasaki Prefecture

Fission-track (FT) dating using both zircon and apatite was performed on sandstone of the Paleogene Kishima Group, Nagasaki Prefecture. The depositional age estimated by zircon FT using two statistical procedures was in good agreement with that estimated by other methods, which shows this method using sandstone is useful for evaluating the depositional age. Zircons ∼60 Ma in FT age were found in the sandstone and were assumed to have originated from Cretaceous granites around near- by Mt. Seburi because of their similarity in zircon FT ages. Because an apatite FT age of 23.8±5.2 Ma was obtained from the sandstone, the studied Paleogene sedimentary basin was assumed to have never experienced temperatures in excess of ∼100degC since 23.8±5.2 Ma. (author)