Complexity in sand and loess deposition in north China evidenced by closely spaced optically stimulated luminescence dating

Category Geomorphology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Lu, Huayu۱; Mason, Joseph۲; Stevens , Thomas۳; Zhou, Yali۱; Yali Zhou, Zhou۱; Yi, Shuangwen۱; Yi, Shuangwen۱
Holding Date 08 September 2008

This study investigates the long held view that Chinese loess deposition is tightly associated with surface variations in desert/sand fields in the north of China. The traditional viewpoint states that when the deserts/sand fields were drier and sand cover was expanded a greater amount of coarse dust particles were emitted and transported onto Chinese Loess Plateau causing higher loess sedimentation rates. In this way the two aeolian systems are tightly coupled at seasonal to orbital timescales and desert/sand field dynamics will have left their imprint in the loess record. However, this model has never been directly tested, especially at centennial-millennial timescales. Here, we compare dust and sand deposition in the desert and loess regions of late Quaternary in North China using independent dating. Closely spaced optically stimulated luminescence (OSL) dates from four typical loess-paleosol sequences along a north-south transect of the Loess Plateau, and twenty sand dune sections in the Mu Us, Otindag and Horqin desert/sand fields, located north of the Loess Plateau, are used to investigate and compare environmental and depositional changes in the two regions. Our results show that surface changes in the desert/sand fields are not always associated with loess deposition at millennial time scales within the error of the OSL dates. Expansion of the desert/sand areas and remobilization of sand dunes appears decoupled from higher sedimentation rates on the Loess Plateau. That is, when the desert/sand areas were dry and presumably emitting more dust, loess sedimentation rates were not always increased. Conversely, a wet period with dense vegetation in the sand fields coincides with a high dust sedimentation rate in the loess region to some extent. These trends are further complicated by the lack of correspondence between sedimentation rates at different loess sections. A potential reason for this decoupling may lie in the likely complex and diverse influences on loess deposition and erosion. Climatic changes are not the unique control these processes and surface conditions such as local landforms, vegetation cover, hydrology and wind intensity changes may also play an important role in the accumulation and preservation of loess. Therefore, in order to reconstruct detailed climatic and environment changes from the loess record, absolute and independent age constraints are needed for these aeolian deposits of late Quaternary.