Baoyin Yuan

Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China

The initial desertification in the Asian interior is thought to be one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic era. But the dating of this transition is uncertain, partly because desert sediments are usually scattered, discontinuous and difficult to date. Here we report nearly continuous aeolian deposits covering the interval from 22 to 6.2 million years ago, on the basis of palaeomagnetic measurements and fossil evidence. A total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils. This new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch, at least 14 million years earlier than previously thought. Regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in Asia.

Earliest presence of humans in northeast Asia

The timing of the earliest habitation and oldest stone technologies in different regions of the world remains a contentious topic in the study of human evolution. Here we contribute to this debate with detailed magnetostratigraphic results on two exposed parallel sections of lacustrine sediments at Xiaochangliang in the Nihewan Basin, north China; these results place stringent controls on the age of Palaeolithic stone artifacts that were originally reported over two decades ago. Our palaeomagnetic findings indicate that the artifact layer resides in a reverse polarity magnetozone bounded by the Olduvai and Jaramillo subchrons. Coupled with an estimated rate of sedimentation, these findings constrain the layers age to roughly 1.36 million years ago. This result represents the age of the oldest known stone assemblage comprising recognizable types of Palaeolithic tool in east Asia, and the earliest definite occupation in this region as far north as 40° N.

Optically stimulated luminescence dating of cave deposits at the Xiaogushan prehistoric site, northeastern China

The Xiaogushan cave site is one of the most important prehistoric sites in North China. The stone and bone artifacts found in the cave are similar to European contemporaneous artifacts. Cave deposits consist of five layers that have been dated from 46,353 ± 1179 to 4229 ± 135 cal. yr BP, using radiocarbon dating techniques on charcoal and bone samples collected from Layers 2-5. In this paper, optically stimulated luminescence (OSL) techniques were applied to date six samples taken from Layers 1-3. The luminescence properties of the fine-grained and coarse-grained quartz extracts indicate that the materials are suitable for OSL dating using a single-aliquot regeneration-dose (SAR) protocol. The OSL ages obtained are broadly consistent with the stratigraphy and the associated calibrated radiocarbon ages. The dating results show that the cave was first occupied by humans about 70 ka. The human occupation of the cave may be related to climate change. An occupation hiatus is inferred to between ∼ 17 to ∼ 10 ka. The stone and bone artifacts found in Layers 2 and 3 may indicate the Middle to Upper Paleolithic transitions in the region.