Guangrong Dong

The distribution of velocity and energy of saltating sand grains in a wind tunnel

Abstract Sand transport by wind is a special case of two-phase flow of gas and solids, with saltating grains accounting for about 75% of the transport rate. This form of flow is not only the main external agent moulding aeolian landforms but also the motive force responsible for transport, sorting and deposition of aeolian sediments. High-speed multiflash photography is an effective method of studying the distribution of velocity and energy of saltating grains within the boundary layer of wind tunnel. The experimental wind shear velocities were set at 0.63, 0.64, 0.74 and 0.81 ms −1 . The statistical study of the results showed that there is a power function relation between mean velocity and height of saltating grains. As the height is divided into 0.5-cm intervals, the sand grain velocities at various levels are consistent with the Pearson VII distribution pattern. The variations in kinetic energy and total energy of sand grains with height accord with the pulse peak modified with power term (Pulsepow) law; the maximum values occur at heights of 6 cm or so and tend to shift upward with increasing wind velocity.

Reconstruction of the spatial patterns of desert/loess boundary belt in North China during the Holocene

The desert/loess boundary belt is the transitional region between desert and loess, where aeolian sand and loess interlock in space and alternate in time. It, being seriously unstable in space-time, sensitive to climatic changes and with fragile ecological environment, is an ideal region for studying the global climate change. There are depositional sequences of paleosol with sub-horizontal interbedded aeolian sand and loess, and the stratigraphical evidences show that there widely exist 3–4 layers paleosol in sand lands of northeastern China, 4–5 layers in Mu Us Sandy Land and Hunshandake Sandy Land, more than 4 layers in the Qinghai Lake region and the Gonghe Basin of Qinghai Province during the Holocene. These indicate that the desert has experienced several times of extending and compacting, along with which the desert/loess boundary belt vibrated. It possesses good coherence with global climate change and eustasy. The coherence shows that the monsoon change in East Asia is the primary driving factor for the swing of desert/loess boundary belt. Besides, human influence constantly intensified the swing of the belt, especially in the south of Mu Us Sandy Land during the 2000–3000 aBP.

Climate instability in the Yili region, Xinjiang during the last glaciation

The climate is influenced by westerlies year in year out and the aeolian loess is widespread in the Yili region, the Xinjiang Uygur Autonomous Region. Through the study of the loess section with a thickness of 21.5 m, much useful information about climatic change in this region during the last glaciation was gotten. Grain size analysis of loess samples in the section showed that the climatic change in the Yili region was of instability during the last glaciation and similar to those of the North Atlantic Ocean and Greenland. In correspondence with the Heinrich events, the percentage of the size fraction of loess with grain size less than 10 μm decreased in cold stadials in the Yili region. This result suggests that the westerly wind be strengthened during the cold periods. Compared with the stadials, the content of the loess with grain size less than 10 μm was increased in interstadials, which indicated that the strength of the westerly wind was weakened. It is obvious that the climate was instable not only in the North Atlantic Ocean and polar regions, but also in other areas of Northern Hemisphere during the last glaciation.

Preliminary results of the study on wind erosion in the Qinghai-Tibetan Plateau using137Cs technique

The worldwide fallout of caesium-137 (137Cs) associated with the nuclear weapon tests during the 1950s and 1960s has provided a valuable man-made tracer for studies of soil erosion and sediment delivery. But relatively few researchers have used it to estimate wind erosion. In this note, the137Cs technique is introduced into the studies of wind erosion and its modern processes in the Qinghai-Tibetan Plateau. Two137Cs reference inventories of 982.11 and 2 376.04 Bq · m−2 were established preminarily, distributed in the south and middle-north parts of the studied area respectively. By analyzing the patterns of137Cs depth profiles from sampling sites, the aeolian processes of erosion and deposition in nearly 40 years have been revealed, i.e. the shrub coppice dunes (S1) and semi-fixed dunefields (S3) experienced the alternation of erosion and deposition, while the grasslands (S4, S6 and S7) and dry farmlands (S5) suffered erosion only. By using137Cs model, the average wind erosion rates for shrub coppice dune (S1), semi-fixed dune fields (S3), dry farmlands (S5) and grasslands (S4, S6 and S7) were estimated to be 84.14, 69.43, 30.68 and 21.84 t · ha1 · a−1 respectively, averaging 47.59 t · ha−1 · a−1 for the whole plateau, which can be regarded as of the medium erosion standard. These results derived from Cs for the first time have significant implications for the further research of wind erosion and desertification control in the Qinghai-Tibetan Plateau.

The trajectory parameters analysis of saltating sand grains driven by wind

The study of trajectory parameters of saltating sand grains is of great importance to forming the kinematic theory of wind-sand current. By establishing the simplified theoretical pattern and probing into the relationship between lift-off angle (α) and landing angle (β), relationship between the ratio of saltation length (L) to maximum height (H) and lift-off angle as well as the angular variation laws of any point on the trajectory, it has been demonstrated that the relations among these parameters are nonlinear. Meanwhile, it has also been proved that the theoretical analysis is basically reliable in accordance with the wind tunnel experiments using high-speed multiflash photography. Generally, the trajectory shapes of saltating sand grains are controlled precisely and the theoretical analysis is closely combined with the experimental results.

New views on age of the Salawusu Formation of Late Pleistocene in northern China

The Salawusu Formation in the Salawusu River basin of Inner Mongolia is a typical sequence of the Upper Pleistocene in northern China. However, there have been some different views about the division and age of stratigraphic facies since the establishment of the Salawusu Formation. According to the stratigraphic subdivision and dating of the Dishaogouwan section, it is thought that the fluviolacustrine-aeolian sand sequence from the Dishaogouwan section can be compared with loess, deep-sea deposit records and climatic fluctuations of glacial period. The Salawusu Formation of fluiolacustrine facies was formed in the last interglacial period from 140 to 70 ka BP, roughly corresponding to the fifth stage of deep-sea oxygen isotope, and developed in the same period as the palaeosol S1 on the Loess Plateau; the aeolian sand of the Chengchuan Formation was formed in the last glacial period from 70 to 10 ka BP, constituting the heteropic geological body along with the Malan Loess on the Loess Plateau; the fluviolacustrine deposit and black soil of the Dagouwan Formation and the Dishaogouwan Formation was formed in the Holocene warm period from 9 700 to 3 000 a BP, or developed in the same period as the plaeosol S1 on the Loess Plateau.

Discovery of Ordos Cretaceous dune rock and its significance

It has been found that there existed quite a large quantity of dune rocks in the red sandstone of the Zhidan Group of Ordos Cretaceous strata. Their sedimentary structure, grain size and micro-shape of sand grains show an obvious aeolian features. Both the temporal and spatial distribution and sedimentary characteristics of these dune rocks suggest that probably a large sand sea once existed in the Ordos region. It belonged to a subtropical inland trade-wind desert with persistent hot climate and was also an important part of the Cretaceous red desert in China.

137Cs tracing of lacustrine sediments in the Dalian Lake, Qinghai Province, China

Based upon the analysis of137Cs and grain-size parameters, the total amounts of137Cs deposition by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province are defined. The vertical profile of Cs in the lacustrine sediments exhibits three137Cs activity maxima and one minimum. The major maximum corresponds to the global137Cs fallout in 1963; the two secondary maxima correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994, respectively. The minimum corresponds to aeolian deposition caused by extensive reclamation in the late 1980s and early 1990s. The137Cs data set was used to evaluate average sedimentation rate of the Dalian Lake since 1963. The deposition was stable in 1963–1986 and 1994–1998, and it was rapid during 1986–1994. This preliminary study reveals that137Cs has the same potential to trace environmental changes introduce by human interference in arid/semiarid regions as in humid regions.

Uplift processes for the Qinghai-Tibet Plateau: A comparative study of Yecheng section and Siwalik group

Comparative studies of the Yecheng section at the northern piedmont of the Kunlun Mountain, and the Surai Khola section at the southern piedmont of the Himalayan Mountain, indicates that the Qinghai-Tibet Plateau is dominated by continuous uplift over the past 10 Ma. And the effective time scale for dividing the uplift stages would be 1 Ma. The uplift processes of the entire plateau can be divided mainly into three stages, i.e., a slow uplift stage (10.0—6.0 MaBP), a transitional uplift stage (6.0—2.5 MaBP) and a rapid uplift stage (since 2.5 MaBP). The plateau might have risen to 2000 m above sea level by 4.6 MaBP in response to uplift and to more than 3000 m by 2.5 MaBP.