Li Bao-sheng

Processes of the deposition and vicissitude of Mu Us Desert, China since 150 ka B.P.

Abstract“Milanggouwan stratigraphical section” named lately takes down 27 cycles of alternately evolutionary histories of desert depositions in the Mu Us area with the fluviolacustrine facies and palaeosols since 150 ka B. P. Studies show that the sedimentary form was induced by the growth and decline and confrontation each other between the winter monsoon and the summer monsoon of East Asia in the past 150 ka.

Grain-size cycles in Salawusu River valley since 150 ka BP

The palaeo-mobile dune sands and fluvio-lacustrine facies with palaeosols in Milanggouwan stratigraphic section of the Salawusu River valley situated at the southeast of the Mu Us Desert experienced abundant remarkable alternative changes of coarse and fine rhythms in grainsize since 150 ka BP, and the grain-size parameters — Mz, σ, Sk, Kg and SC/D also respond to the situation of multi-fluctuational alternations between peak and valley values. Simultaneity the grainsize eigenvalues — ϕ5, ϕ16, ϕ25, ϕ50, ϕ75, ϕ84 and ϕ95 are respondingly manifested as greatly cadent jumpiness. Hereby, the Milanggouwan section can be divided into 27 grain-size coarse and fine sedimentary cycles, which can be regarded as a real and integrated record of climate-geological process of desert vicissitude resulted from the alternative evolvement of the ancient winter and summer monsoons of East Asia since 150 ka BP.

Sedimentary cycles of trace elements in Salawusu River Valley since 150 ka BP

The paper makes some analyses on 11 trace elements in the Milanggouwan stratigraphical section in the Salawusu River valley, which is regarded as a prototype geology-palaeoclimate record since 150 ka BP. The results show that the content and variation of trace elements has experienced remarkably regular changes in the pace with coarse and fine sedimentary cycles of palaeo-aeolian sands to its overlying fluvio-lacustrine facies or/and palaeosols. The trace elements with chemical properties of relatively active (V, Sr, Cu, Ni, As) and relatively stable (P, Pb, Rb, Mn, Nb, Zr) are a manifestation of the corresponding 27 changeable cycles between peak and valley values, appearing a multi-fiuctuational process line of relative gathering and migration since then. The low numerical value distribution of these two types of trace elements in the aeolian sand facies represents erosion and accumulation under wind force during the cold-dry climate. Whereas their enrichments in both fluvio-lacustrine facies and palaeosols are related to the valley’s special low-lying physiognomic position between the Ordos Plateau and the Loess Plateau under the warm and humid climate conditions. The above relatively migrated and gathered change of the trace elements is the result of 27 climatic cycles of cold-dry and warm-humid, which is probably caused by repeated alternations of winter monsoon and summer monsoon in the Mu Us Sandy Land influenced by the climate vicissitudes in northern hemisphere during glacial and interglacial periods since 150 ka BP.

Deposition of sandstorms in a vegetation-covered sand dune in Ejin Oasis and its characteristics

Abstract“Ejin Section” found in a typical vegetation-covered sand dune in Ejin Oasis was investigated. In this study, 263 samples were taken from the section for grain-size analysis, 25 for chemical analysis, 11 for 14C dating and 6 for scanning electron microscope (SEM). The results of the study indicate that 3 types of the sediments in the section can be identified, YS, LS and ST. YS, homogeneous yellow-brown dune sands, is equal to those of inland deserts, LS, loess-like sandy soils, is the same as the sandy loess in the middle Yellow River and modern falling dusts, and ST, sandy sediments interbeded with the deadwood and defoliation of Tamarix spp, represents the depositional process of the section interrupted by abrupt changes in climate. The Ejin Section has recorded the repeated dust-storms or sandstorms since 2500 yr BP and the peak periods of the dust-storms or sandstorms revealed by the section are consistent with the records of “dust rains” in historical literatures, indicating that the change of climate is a key factor to increase sandstorms or dust-storms, whereas, “artificial” factor may only be an accelerating one for desertification.

Distribution pattern and expansion mechanism of financial institution network in the Yangtze River Delta

Luoji Mountain located at the southeast margin of the Qinghai-Tibet Plateau is one of the typical mountains in China where Quaternary glacier relics exist. The evolution of glacier landforms in the area plays an important role in the study of regional environmental change. In the Qingshui Valley on the east slope of the Luoji Mountain, two sets of ancient glacial trough valleys, namely the inner trough valley and lateral trough valley,are preserved. The inner trough valley is relatively intact. However, the lateral trough valley between 3450 m and3600 m in the shady slope is incomplete. Based on field investigation and model analysis, this study examines the evolution of the glacial trough valley. The model analysis shows that the A and B parameter values vary between 1.3101-15.2064 and 0.9695-3.2965 respectively and these values first increase and then decrease with decreasing altitudes. Both values indicate that the form of the glacial trough valley is atypical. The field investigation and model analysis indicate that lithology and headwater erosion have contributed to the shape of the trough valley. This study applied the ESR dating method to define the high and low moraine in the through valley. The result shows that the high lateral moraine was formed in ~58-84 ka BP, which was in the early stage of the last glacial cycle, corresponding to the Marine Isotope Stage 4(MIS4). The low lateral moraine was formed in 13-17 ka BP, which was during the last glacial maximum(LGM), corresponding to MIS 2. During the last glacial cycle two glaciations developed two sets of trough valleys respectively, that is, the early stage of the last glacial cycle contributed to the formation of the lateral trough valley, and the late stage of the last glacial cycle contributed to the formation of the inner trough valley. The glacial sequences in the Qingshui Valley also show that the glacial activities took place here accorded with other mountains in the surrounding areas of the Qinghai-Tibetan Plateau.