Apatite U–Pb dating of dinosaur teeth from the Upper Cretaceous Nemegt Formation in the Gobi Desert, Mongolia: Contribution to depositional age constraints

The Nemegt Formation in the Gobi Desert, Mongolia, hosts abundant dinosaur and other vertebrate remains, the ages of which are uncertain due to a lack of radioactive dating. In order to more strictly constrain the depositional age of Nemegt Formation, we conducted U–Pb isotope, trace elements, and Y-screening analyses using laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) on apatites of five Tarbosaurus bataar teeth collected from the middle Nemegt Formation. As a result, the age of 66.7 ± 2.5 Ma was obtained from one of the samples which is suggested to be least affected by secondary alteration of the U distribution, and this can be interpreted as a lower limit for fossilization of the tooth samples. Combined with the previously suggested relative age of the Nemegt Formation based on faunal occurrences, our data supports the deposition of the middle–upper Nemegt Formation during the Maastrichtian stage. Given that the depositional age of the Nemegt Formation has not been examined by isotope dating directly using fossils and minerals from the formation, this study is the first to report that the depositional ages of the vertebrate-bearing strata in the Gobi can be discussed by fossil apatite U–Pb dating in combination with the Y-screening method.