GEOGRAPHIC DIFFERENTIATION OF THE LAST INTERGLACIAL PALEOSOL S1 IN THE CHINESE LOESS PLATEAU

The net eolian deposition attenuated while the pedogenesis intensified southeastward during the last interglacial in the Chinese Loess Plateau. Consequently, the last interglacial paleosol S1 gradually differentiated from the southeast to the northwest as follows. In the southeastern part, multiple soil-forming events occurred in a single completely welded soil profile. Towards the northwest, climate becomes drier and the loess becomes thicker, and the multiple soils become partially welded (i.e., subsequent soils "annexed" the upper portions of previous soils). Moving further towards the northwest, each one of the multiple soils becomes completely separated. In the northwestern part, not only are the multiple soils completely separated, but also the loess units between the soils are well preserved. In all cases investigated, the coarse fraction content well defines the upper and lower boundaries of the S1 parent material and can be used to estimate the time-transgressive nature of the S1 paleosol relative to its parent material. Soil welding, bioturbation and material translocation (e.g., clay and carbonate) within the S1 profiles make it impossible to preserve the high-resolution information of the last interglacial (128-73 ka) climate changes in most parts of the Chinese Loess Plateau. First, clay translocation within the S1 profiles has moved some of the magnetic minerals downward so that the susceptibility only reflects the post-translocation distribution of the susceptibility-producing minerals. Second, the best-developed paleosol S1S3 (i.e., MIS 5e) at most of the sections is not expressed by the susceptibility because the S1S3 developed into underlying coarser and lower-susceptibility loess (i.e. L2). Third, the carbonate concentration dilutes the susceptibility signature. At most of sections investigated, the post-depositional in situ weathering and the post-weathering clay translocation within the S1 profile occurred and post-depositional carbonate leaching and accumulation are observable throughout the S1 profiles. Equally important is the downward development of the S1 into the underlying coarser loess (L2). These mean that both the susceptibility (summer monsoon proxy) and the particle size (winter monsoon proxy) are problematic as quantitative climatic proxies.