Magnetostratigraphic dating of the Pulu mammalian fauna in the Nihewan Basin, North China

Nihewan Basin is one of a series of well-developed East Asian Cenozoic basins in Hebei Province, North China, which are rich sources of mammalian faunas and Paleolithic sites. During the past decades, detailed magnetostratigraphic dating was conducted on the Nihewan Formation and associated mammalian faunas and Paleolithic sites, and the results have contributed significantly to our understanding of the chronostratigraphy of the Nihewan Basin.

The Pulu fauna, one of the Nihewan faunas (sensu lato), is located on the eastern bank of the Huliu River in the Nihewan Basin and contains mammalian fauna in the late Pliocene to early Pleistocene. Here, we selected the fluvio-lacustrine deposits containing the Pulu mammalian fauna to conduct detailed rock magnetic and high-resolution magnetostratigraphy studies, combined with biostratigraphic and lithostratigraphic results, to precisely constraint on the Pulu mammalian fauna. In this study, 466 oriented samples were collected from the fluvio-lacustrine sequences of Pulu section (thickness 112 m) for detailed rock magnetic and magnetic fabric studies. The results showed that the magnetic minerals in the fluvio-lacustrine deposits of the Pulu section are mainly magnetite, maghemite and hematite, with predominantly pseudo-single domain. The Pulu fluvio-lacustrine deposits recorded the early Brunhes normal chron, the Matuyama reverse chron, the Gauss normal chron and the late Gilbert reverse chron. The Pulu mammalian fauna was found during the pre-Réunion Matuyama chron and the post-Kaena Gauss chron with the age about 3.0-2.2 Ma. This study has extended the lower age of the Nihewan faunas to about 3.0 Ma. Furthermore, the paleoclimatic and paleoenvironmental studies in the Nihewan Basin suggested that the evolutionary direction of the Nihewan faunas were influenced by changes in climate and environment during the Pliocene and Pleistocene transitions, and Nihewan faunas evolved towards adapting to a cold and arid environment.