10:15 〜 10:30
[MIS13-06] モンゴル国ゴビ砂漠の恐竜歯化石年代測定の試み
★招待講演
Our research group (Okayama University of Science) and the Institute of Paleontology, Mongolian Academy of Sciences have collaboratively conducted studies on the geology of Cretaceous strata and their vertebrate fossils in the Gobi Desert, Mongolia. In this session, we introduce some of them, focusing on apatite U-Pb dating of dinosaur teeth in that area.
The Gobi Desert, Mongolia, hosts abundant dinosaur and other vertebrate remains, the ages of which are uncertain due to the lack of radioactive dating. 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 uppermost formation of Upper Cretaceous in the Gobi Desert. As a result, the age of 66.2 ± 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 formation based on faunal occurrences, our data support that the deposition of the formation occurred during the Maastrichtian. 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. Another important result of this study is the reaffirmation that the Y-screen method is a powerful tool as an indicator of the alteration of tooth fossils. We will present the additional analyses, Y-map measurement and the subsequent apatite U-Pb dating, on the same teeth showing the reasonable absolute age.
The take-home messages of our study are apatite U-Pb dating in combination with the Y-screening method on vertebrate teeth does not solely represents meaningful geological ages, yet when combined with existing age data, it provides important supporting data to further constrain the depositional ages of fossil-bearing strata and the temporal ranges of the fauna.
The Gobi Desert, Mongolia, hosts abundant dinosaur and other vertebrate remains, the ages of which are uncertain due to the lack of radioactive dating. 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 uppermost formation of Upper Cretaceous in the Gobi Desert. As a result, the age of 66.2 ± 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 formation based on faunal occurrences, our data support that the deposition of the formation occurred during the Maastrichtian. 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. Another important result of this study is the reaffirmation that the Y-screen method is a powerful tool as an indicator of the alteration of tooth fossils. We will present the additional analyses, Y-map measurement and the subsequent apatite U-Pb dating, on the same teeth showing the reasonable absolute age.
The take-home messages of our study are apatite U-Pb dating in combination with the Y-screening method on vertebrate teeth does not solely represents meaningful geological ages, yet when combined with existing age data, it provides important supporting data to further constrain the depositional ages of fossil-bearing strata and the temporal ranges of the fauna.