Calcite U-Pb age of the Cretaceous vertebrate-bearing Bayn Shire Formation in the Eastern Gobi Desert of Mongolia: Usefulness of caliche for age determination

摘要

To verify the usefulness of calcite U-Pb measurement for vertebrate-bearing strata in the Eastern Gobi, Mongolia, we performed laser ablation-inductively coupled plasma-mass spectrometry calcite U-Pb and trace element analyses of three caliche (calcrete) of the Bayn Shire Formation. The trace element analysis demonstrates high concentration of U in the calcites. Two meaningful calcite U-Pb ages were obtained; 95.9 +/- 6.0 and 89.6 +/- 4.0 Ma, which are consistent with published ages from the Bayn Shire Formation. Our results demonstrate that the calcite U-Pb method can be powerful tool for age determination of vertebrate-bearing strata in the Gobi that do not contain index fossils or beds, but do contain caliches. This would make it possible for a comparison of biostratigraphy between the Gobi and other areas yielding abundant vertebrate fossils in Asia, North America and Europe, based on chronological data.