Yuan Baoyin

Changes in hydrological conditions in the central Qing-Zang (Tibetan) Plateau inferred from lake bottom sediments

Abstract Grain particle and chemical analyses of core samples obtained from Siling-co, a lake on the central Tibetan Plateau, and a sedimentation model for the lake with 14 C dating show fluctuations in the hydrological environment of the area during the past 15,000 yr. The area of the lake was small and the water level low in the late part of the last glacial period. Thereafter, the lake became larger and the water level high because of meltwater and rainfall. This hydrological environment continued until 4000 yr B.P., at about which time the level of the lake fell sharply and the lake area shrank. After a short period of low level and aridity, the water level increased markedly but did not reach the previous high level. After the large water inflow for a short period, the climate became again arid at about 3500 yr B.P. The change in this interval is closely related to global change. Statistical analyses of the datasets of the grain particle components of bottom sediments preserved in an aquatic condition over the past 13,000 yr show that most datasets for grain size and chemical parameters had a common period of 2000–2200 yr during this interval.

Early Pleistocene hominid teeth recovered in Mohui cave in Bubing Basin, Guangxi, South China

Two hominid teeth recovered in Mohui cave are morphologically distinguished fromAustralopithecus in Africa, but close toHomo erectus in China. These teeth are therefore provisionally assigned toHomo erectus. The associated mammalian fauna includeGigantopithecus blacki, Nestoritherium sp.,Sus xiaozhu, Sus peii andAiluropoda microta, which are typical early Pleistocene taxa in South China. The general characteristics of the Mohui faunal assemblage are similar to the Longgupo site, which is dated to 2 Ma, implying a contemporaneity for the two sites. To date, compared with the discoveries in Africa, far fewer early Pleistocene hominid fossils have been recovered in Asia, and there are intensive controversies concerning their stratigraphic provenience and typological and temporal positions. The hominid fossils from Mohui cave, with their reliable biostratigraphic positions and distinct typological features, provide important evidence regarding the issue of early human origins and evolution.

Geomorphological inheritance for loess landform evolution in a severe soil erosion region of Loess Plateau of China based on digital elevation models

The influence of pre-quaternary underlying terrain on the formation of loess landforms, i.e., the geomorphological inheritance issue, is a focus in studies of loess landforms. On the basis of multi-source information, we used GIS spatial analysis methods to construct a simulated digital elevation model of a pre-quaternary paleotopographic surface in a severe soil erosion area of the Loess Plateau. To reveal the spatial relationship between underlying paleotopography and modern terrain, an XY scatter diagram, hypsometric curve, gradient and concavity of terrain profiles are used in the experiments. The experiments show that the altitude, gradient and concavity results have significant linear positive correlation between both terrains, which shows a relatively strong landform inheritance relationship, particularly in the intact and complete loess deposit areas. Despite the current surface appearing somewhat changed from the original shape of the underlying terrain under different erosion forces, we reveal that the modern terrain generally smoothes the topographic relief of underlying terrain in the loess deposition process. Our results deepen understanding of the characteristics of geomorphological inheritance in the formation and evolution of loess landforms.

The 5000-year environmental change and associated human activities at Sokho-nor Lake, Inner Mongolia, P.R. China

Abstract Sokho-nor Lake is situated in the western part of Inner Mongolia, Northwest China. Human beings have been living in this area since the New Lithic Age. Throughout history, this area has undergone repeated desert-oasis periods, associated with changing river inputs through time. The varying population in the area has been strongly influenced by the water resources available. Inhabitants included members of the Han race and people from northern nomadic tribes. Their activities in the past were affected by changing lake levels. Today, the lake is completely dry, and the environmental impact on the region is a serious problem.

Paleotopographic controls on modern gully evolution in the loess landforms of China

The inhomogeneous and non-flat paleotopography in a depositional landform area profoundly controls the process of modern gully evolution and shapes the structure of a gully network. However, this controlling effect of paleotopography on modern gully evolution is mostly ignored because of the difficulties in paleotopography reconstruction. In this study, loess area in China is selected as case area for its typical depositional landform area and inhomogeneous and non-flat paleotopography during the Quaternary. The paleotopography underlying loess is considered while evaluating its controlling effects on the gully evolutionary process. On the basis of the geophysical prospecting, detailed geological information, and high-resolution digital elevation model, we reconstruct the pre-Quaternary paleotopographic surface in the case area. Comparative analysis is conducted to reveal the modern gully evolution in relation to the paleotopography. Results show that the concave area of the paleotopography acts as the basement of the high-order modern gully evolution in the hilly-gully area, although this concave area can be covered and buried by the loess depositional process during the Quaternary. A significant controlling effect of paleotopography on high-order modern gully evolution can be observed in a depositional landform with a hilly-gully underlying topography, whereas a relatively weak controlling effect exists in a flat underlying topographical area because of the strong horizontal shift effect of gully formation process. Several low-order modern gullies also exist and limit the controlling effect of paleotopography. These results reveal a controlled high-order modern gully evolutionary process and a rather dynamic low-order modern gully evolutionary process in the hilly-gully area. These results also help us understand the variations in different modern gully evolution in relation to paleotopography and the different management schemes for soil conservation and ecological restoration during the gully evolutionary process.