Jin-Liang Feng

The evolution of the modern Luanhe River delta, north China

The Luanhe River Delta is located at the northern coast of the Bohai Bay, which was an enclosed sea. In 1915, the Luanhe River changed course to its present position, and has since developed a typical fan-shaped delta under fluvial-wave interaction. Owing to the water conservancy projects constructed in the catchment, the sand load that the Luanhe River takes into the sea has decreased sharply since 1980. Hence, the evolution of the Luanhe River Delta can be divided into two phases: the delta constructing phase between 1915 and 1979, and the para-abandoned phase after 1979. In the different phases, the delta characteristics are not alike. The main features of the delta evolution are changes in the distribution and development of lagoons. It seems that with the increase in delta construction features there is an increase in lagoon areas. A decrease of lagoon areas indicates the delta dying. Along with further development, the delta flank lagoons expand and the delta tip lagoons tend to shrink. These trends are also present in the processes of the para-abandoned delta phase. In each different stage of development, the delta has a different geometric pattern. At the first stage, the prolate axis of the ellipse fitted to the delta plain outline was perpendicular to the coast, the delta tip had high curvature. Along with the deltas further development, the delta tip curvature gradually decreased and the prolate axis of the ellipse turned to parallel the coast.

Origin of terra rossa on Amdo North Mountain on the Tibetan plateau, China: Evidence from quartz

Abstract Terra rossa was found overlying limestone on a planar erosion surface at approximately 5100 m on the summit of Amdo North Mountain on the Tibetan Plateau. The present study examined the quartz content, size distribution of the quartz grains, mineral composition, oxygen isotope ratios in the quartz, surface microtexture and crystal morphology of the quartz in the terra rossa and its potential source rocks to determine the derivation of the terra rossa. The results indicated that the component of the terra rossa on Amdo North Mountain is a mixture of weathering products from the underlying limestone, the overlying red sandy limestone and the adjacent limestone breccia. These different parent materials can result from being introduced under gravity and other mass transport during geological epoch. Therefore, the terra rossa on Amdo North Mountain is primarily a transported sedimentary deposit, not an in situ weathering solum. The source of much of the terra rossa is likely to be weathering products on adjacent uplands under paleo-landform frame. Multiple sources appear responsible for the terra rossa on Amdo North Mountain. Eolian dust, however, does not appear to have provided a significant addition to the terra rossa formation on Amdo North Mountain.

Potential forcing mechanisms of Holocene lake-level changes at Nam Co, Tibetan Plateau: Inferred from the stable isotopic composition of shells of the gastropod Radix:

The timing of lake-level fluctuations on the Tibetan Plateau and their relationship with climatic changes is still under debate, and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes. Here, we present the results of analyses of the shell geochemistry of Radix sp. from an exposed terrace of Nam Co lake on the south-central Tibetan Plateau. Optically stimulated luminescence (OSL) dating reveals that deep-water lacustrine sediments formed between ca. 4.4 and 2.2 ka, suggesting a high and stable lake level significantly above the present. The results of Sr/Ca, δ13C and δ18O analyses of the fossil shells of Radix sp. indicate that during the mid- to late-Holocene, lake-level variations in Nam Co were mainly controlled by variations in the Indian Summer Monsoon. A trend of decreasing evaporation also played an important role. Comparison with other results suggests a consistent pattern of mid- to late-Holocene lake-level changes across a large area of the Tibetan Plateau and adjacent regions to the south, which had a similar causal mechanism. Finally, our results indicate that fossil shells of the gastropod Radix sp. of the lakes on the Tibetan Plateau are a valuable archive for reconstructing the regional paleohydrology and paleoclimatology.