Yibo Yang

Paleomagnetic Constraints on the Middle Miocene-Early Pliocene Stratigraphy in the Xining Basin, NE Tibetan Plateau, and the Geologic Implications

The Xining Basin lies in the transitional zone between the arid Asian interior and the East Asian monsoon region. The continuous Cenozoic sediments in the basin provide a unique archive recording the uplift of the Tibetan Plateau and its environmental effects on central Asian aridification and Asian monsoon evolution. However, sediments deposited since the middle Middle Miocene have not been precisely dated, hindering our ability to address these issues. Here, we dated a 336-m-thick section containing many Late Miocene fossil mammals from the eastern basin. High-resolution paleomagnetism revealed 16 normal and 16 reversed zones that correlate well with chrons 3n to 5Ar.1r of the Geomagnetic Polarity Time Scale, constraining the section to ∼12.7-4.8 Ma. The changes in lithofacies from floodplain to braided river at ∼8.6 Ma and to thick alluvial fan at ∼6.3 Ma with predominantly southerly paleocurrent directions occur simultaneously with an increase in the sedimentation rates, representing two periods of rapid uplift in the eastern Qilian Shan to the north. Our results provide a robust oldest age constraint (<4.8 Ma) on the ancient Huang Shui and Yellow River terraces on the basin sediments and eolian deposits on the terraces. The presence of well-developed floodplain paleosols, shallow lake marls and many large mammals in the lower section suggests that the monsoon climate in the late Middle Miocene to Late Miocene was more humid and stronger than that at present.

Mineralogical and Geochemical Discrimination of the Occurrence and Genesis of Palygorskite in Eocene Sediments on the Northeastern Tibetan Plateau

Palygorskite is a widely used indicator of semiarid to arid environments in paleoclimate studies. In this study, we present detailed mineralogical and geochemical investigations exploring the genesis of palygorskite found in Eocene fluvial sediment in the northern Qaidam Basin on the northeastern Tibetan Plateau. The presence of two types of palygorskite is revealed, based on their crystallinity characteristics and distinctive rare earth element (REE) patterns in the coexisting clay fraction. Well-crystallized palygorskite samples are characterized by remarkably negative Ce anomalies and obvious middle rare earth element enrichment. Poorly crystallized palygorskite samples generally exhibit positive Ce anomalies and less pronounced middle rare earth element enrichment, which resemble those of nonpalygorskite-bearing clay samples. Given the presence of an overall oxidized fluvial sedimentary environment, we attribute the well-crystallized palygorskite (which has textures comprising long, interwoven fibers) to direct precipitation (i.e., neoformation) occurring within a reducing environment during early/postdepositional processes while the poorly crystallized palygorskite (which is characterized by short, club-shaped single crystals) originates as catchment-delivered detritus. These poorly crystallized palygorskites occur mostly in 49.5-47.0 Ma and are accompanied by decreasing kaolinite content, increasing chlorite content, and abundant xerophytic spore-pollen from the Qaidam Basin, and its neighboring Xining Basin. Collectively, these evidences suggest that a less humid climate followed after the Early Eocene Climate Optimum.

Deep Drilling Campaign in the Western Qaidam Basin, NE Tibetan Plateau and their Revealed Global Temperature Forcing of Salt Formation in the Late Miocene-Quaternary

The Qaidam Basin in the NE Tibetan Plateau has contributed the largest amount of potash in China.However,how the potash was formed has long been a subject of debate.Here we carried out a deep drilling

MEASUREMENT AND PALEOCLIMATIC SIGNIFICANCE OF SOIL BULK DENSITY FOR LOESS IN EXTREME ARID REGION: MEASUREMENT AND PALEOCLIMATIC SIGNIFICANCE OF SOIL BULK DENSITY FOR LOESS IN EXTREME ARID REGION

Soil bulk density of the loess-paleosol can not only reflect variations in strength of East Asian winter and summer monsoon,but also has important significance to study paleoclimate and reconstruct drying trend of Asian heartland.Now,most of researches on the soil bulk density concentrate their attention on Chinese Loess Plateau(CLP),while in the arid regions of Northwest China there are relatively fewer researches on the methods and paleoclimatic significance of the soil bulk density.Based on previous studies,an ideal method for measurement of the soil bulk density in arid region of Asian heartland is put forward in this paper,and we also find the soil bulk density value in negative correlation with variations in the grain sizes and magnetic susceptibility(MS),which is very different from that in Chinese Loess Plateau.Further analysis suggested that variations in the soil bulk density of extreme arid region loess was mainly controlled by the drought extent of source region,rather than monsoon intensity.