Pleistocene magnetochronology of the fauna and Paleolithic sites in the Nihewan Basin: Significance for environmental and hominin evolution in North China

摘要

The fluvio-lacustrine sequences in the Nihewan Basin of North China (known as the Nihewan Formation) are rich sources of Early Pleistocene Paleolithic sites and mammalian fossils (known as the Nihewan Fauna sensu lato), which offer an excellent opportunity to investigate the evolution of early humans and land mammals in East Asia. Also abundant mammalian fossils provide clues about the general environmental and climatic setting of early humans. Among the Nihewan Fauna (sensu lato), the Daodi Fauna is one of the most complete and oldest in the eastern Nihewan Basin: seven mammalian fossil-bearing layers in the Nihewan Formation have been described. Except for a biostratigraphy, however, precise age control on the Daodi Fauna has remained unavailable. Here we report a new magnetostratigraphic record that stringently constrains its age. The seven fossil-rich layers span an age range of ca 2.5-1.8Ma between the Gauss-Matuyama boundary and the termination of the Olduvai polarity subchron. Combining our new and recently published paleomagnetic data, we further establish a Pleistocene magnetochronology of the fauna and Paleolithic sites in the Nihewan Basin. Age ranges of about 2.5-0.5Ma for the faunas and 1.7-0.3Ma for the Paleolithic sites are deduced, which span most of the Pleistocene. The chronological framework and calculated proportions of mammals that were adapted to different environments indicate that mixed settings of dominant grasslands and subordinate forests continued at least from 2.5 to 0.5Ma for early human occupation in the basin, similar to the mixed open savannah and woodland habitats of early humans in Africa. The Nihewan hominins consistently adopted a simple Oldowan-like technology (i.e., Mode 1 core and flake technologies) from at least ca 1.7 to 0.3Ma. A more advanced Acheulean technology (Mode 2) has not been found in the Nihewan Basin, although it started to emerge in the Bose Basin of South China at ca 0.8Ma. This implies that multiple groups of hominins distinguished by differential stone-tool-making capabilities may have coexisted in China after 0.8Ma.