High-precision temporal calibration of Middle Triassic vertebrate biostratigraphy: U-Pb zircon constraints for the Sinokannemeyeria Fauna and Yonghesuchus

分类： 地球科学 >> 地质学 提交时间： 2017-08-24 合作期刊: 《古脊椎动物学报》

LIU Jun Jahandar RAMEZANI LI Lu SHANG Qing-Hua XU Guang-Hui WANG Yan-Yin YANG Jia-Sheng

摘要： Tetrapod assemblages provide a useful means for global correlation of the terrestrial Triassic sedimentary deposits, but currently no reliable temporal framework has been achieved for the Middle Triassic tetrapod assemblages. Here we report U-Pb zircon chemical abrasion–thermal ionization mass spectrometry dates for five volcanic ashes interbedded with vertebrate fossils from the Ermaying and Tongchuan formations of China. Our results support a late Anisian age for the Sinokannemeyeria Fauna and an early Ladinian age for Yonghesuchus Fauna. It is now possible, through biostratigraphic correlation, to provide accurate ages to other Middle Triassic successions such as the Upper Cynognathus Assemblage Zone of the Karoo of South Africa, the Eryosuchus fauna of the Donguz Suite of Russia and the Karamayi Formation of Xinjiang, China. The base of Anisian (Lower/Middle Triassic boundary) should lie below the base of the Ermaying Formation in the Ordos Basin. 四足动物组合带是全球陆相三叠系对比的有力手段，但是迄今为止中三叠世的四足动物组合尚没有可靠的时间框架。本文报道了五个采自二马营组和铜川组，与四足动物化石共同产出的火山凝灰岩样品的锆石化学剥蚀-热电离质谱法年龄。结果表明中国肯氏兽动物群时代为安尼期晚期，而永和鳄的时代为拉丁期早期。通过生物地层对比，这一结果还为其他中三叠世的四足动物组合，如南非的犬颌兽带上部、俄罗斯的引鳄动物群以及新疆的克拉玛依组提供了准确的年龄。鄂尔多斯盆地下中三叠统界线应低于二马营组底界。

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