Isochron 26Al/10Be burial dating of the Xiashagou Fauna in the Nihewan Basin, northern China: Implications for biogeography and early hominin dispersals

The Nihewan Basin in northern China is one of the most dense occurrences of Early Pleistocene vertebrate paleontological and Paleolithic sites outside of Africa and thus plays a key role in the study of biochronostratigraphy and early human evolution in East Asia. The Xiashagou Fauna, as the first systematically studied fauna in the basin, is usually referred to as the Nihewan Fauna (sensu stricto) and is considered the Early Pleistocene type fauna in northern China, serving as a key reference for biostratigraphical correlations. The Xiashagou Fauna was initially correlated with the Olivola Fauna of early Late Villafranchian age in Europe, dated to ∼1.8 Ma. It has been more recently constrained to the Matuyama chron between the Réunion and Olduvai subchrons, with an estimated age range of 2.2–1.7 Ma. However, there is still an absence of absolute dates associated with this important Fauna. Here, the isochron 26Al/10Be burial dating method was used to radio-isotopically verify the biostratigraphic and magnetostratigraphic age of the Xiashagou Fauna. Two sets of quartzose clasts were collected from the cross-sections near Xiashagou. The isochron burial age of six samples from one of the fossil-bearing layers is 2.05 ± 0.38 (0.39) Ma (bracketed uncertainty includes external systematic errors, ±1σ), in agreement with previous paleomagnetic estimates of 2.2–1.7 Ma. The isochron age of another five samples from a gravel layer about 80 m below the sampled fossil layer and 55 m beneath the deepest buried fossil layer is 2.43 ± 0.16 (0.18) Ma (±1σ), in agreement with previous paleomagnetic estimates of 2.58 Ma. Our results show that the age of the Xiashagou Fauna is consistent with the updated ages (2.21–1.95 Ma) of the Senèze and Olivola Faunas in Europe. The potential existence of an ecological corridor for faunal dispersals across northern Eurasia during this time period should be important to help contextualize the nature of the earliest hominin dispersals into and across Eurasia. As the first radio-isotopic ages for the Nihewan Basin sites, our results provide independent age control to anchor the magnetostratigraphy of the Early-Middle Pleistocene strata in the Nihewan Basin and to calibrate the Early Pleistocene stage of the Chinese Quaternary.