State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
Paleomagnetic Laboratory 'Fort Hoofddijk', Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands.
Sci Rep. 2016 Nov 30;6:38023. doi: 10.1038/srep38023.
A large number of terrestrial mammalian fossils were reported in the well-exposed Paleogene and Neogene fluvio-lacustrine strata in Western China. Their accurate ages are crucial to understand the mammalian and environmental evolution associated with the step-wise uplift of the Tibetan Plateau. At present their ages are surprisingly poorly constrained. Here, we present a high-resolution magnetostratigraphic dating of the Late Oligocene-Early Miocene mammal assemblages from a 233-m thick fluvio-lacustrine section in the Lanzhou Basin located at the northeastern margin of the Tibetan Plateau, China. The results suggest that the section spans from the polarity subchron C6Cn.2r to C5En, i.e. ranging from ca 23 to 18 Ma. This magnetochronology provides considerably more robust ages for three associated land mammalian faunal assemblages. Updated ages end the debate on existing ambiguous and distinctly different magnetostratigraphic correlations for those Late Oligocene-Early Miocene assemblages. The new ages now enable precise correlation of these faunas to the European Land Mammal and North American Land Mammal Ages. The faunal assemblages further suggest a mixed setting of woodlands and grasslands associated with a humid environment in the Lanzhou Basin during the Late Oligocene-Early Miocene, in contrast to its modern poor vegetation cover and arid environment.
在中国西部,大量的陆生哺乳动物化石在暴露良好的古近纪和新近纪河湖相地层中被报道。它们的准确年龄对于理解与青藏高原逐步隆升相关的哺乳动物和环境演化至关重要。目前,这些化石的年龄出人意料地没有得到很好的约束。在这里,我们对青藏高原东北部兰州盆地一个 233 米厚的河湖相剖面的晚渐新世-早中新世哺乳动物组合进行了高分辨率的磁性地层年代测定。结果表明,该剖面跨越了极性亚时 C6Cn.2r 到 C5En,即大约 23 到 18 百万年前。这个磁性年代学为三个相关的陆生哺乳动物化石组合提供了更可靠的年龄。更新后的年龄结束了对这些晚渐新世-早中新世组合存在的模糊和明显不同的磁性地层对比的争论。这些新的年龄现在使得这些化石能够与欧洲陆地哺乳动物和北美陆地哺乳动物时代进行精确的对比。这些化石组合进一步表明,在晚渐新世-早中新世期间,兰州盆地的环境是混合的林地和草原,与现代贫瘠的植被覆盖和干旱环境形成鲜明对比。