U-Pb constraints Late Miocene Hipparionine fauna stratigraphic age at 7.26 Ma

Abstract

This paper presents the first application of U-Pb dating to resolve the geological age of the Late Miocene mammalian fauna. Five fossil beds containing late Miocene mammalian fauna can be found in northern China, which include fossil specimens of Hipparion chiai, is most fixed time indicator fossil. However, the geological age of the fossil belt is still unresolved. Absolute dating of sedimentary rocks and fossils from the late Miocene is still rare, mainly due to the difficulties arising from suitable absolute dating technique and sample diagenetic changes. Biological Apatite (carbonated Hydroxyapatite) in the teeth fossils of Hipparion chiai contain Uranium, high μ value (the initial value of 238U/204Pbi), limited Th content and remain relatively unchanged due to their resistance to diagenetic alterations. Here, we first derived six fossil teeth of Hipparion chiai were sampled from the Wangdafuliang section in Fugu, in the Shaanxi Province, and were dated using the U/Pb method to obtain an absolute age. The U-Pb dates obtained from the six fossil teeth of Hipparion chiai varied, ranging from 6.87±0.13 Ma to 7.71±0.39 Ma (2 s), with an average of 7.26 Ma. This result provides a new basis for determining the age of the Hipparion chiai-Dinocrocuta gigantean-Hezhengia-Shaanxispira standard fossil belt (index fossil assemblage) from the Late Miocene in northern China. The belt is probably 7.26 Ma, rather than previous estimates of 10–9 Ma. The absolute dating of fossils, in turn, bring about a new revolution in Biostratigraphy and establish the geochronology of sedimentary sequences at sub-millennial timescales, especially those early Cenozoic stratigraphy that is absent of an suitable absolute dating technique.