| The Holocene loess-soil sequence in the Loess Plateau constitutes an excellent record of evolution of soil formation, monsoonal climate, aeolian dust accumulation and influences of arable farming of over 8000 years. In this study, three typical high-resolution Holocene soil profiles in the Weihe valley were studied using particle-size analysis, measurement of magnetic susceptibility, total Fe, TOC, CaCO3, rare earth elements and others. The results provide new insights into pedogenic environmental evolution and human impact of cultivation on soil development in this climatically sensitive semiarid zone.The main results are following:(1) The variation of clay/silt ratio can indicate the secondary clay action of dust depositions; the variations of magnetic susceptibility and total Fe content are inferred to be records of the changeable intensity of bio-pedogenesis; the variations of Sr content and Rb/Sr ratio can indicate bio-pedogenesis, dissolving and leaching action; the content of total organic carbon (TOC) can reflect variation of climate and vegetation during soil formation, it indicates the intensity of weathering and bio-pedogenesis; the content variation of CaCO3 can show the intensity of dissolving-leaching action and secondary deposit, which was noted as pseudomycilia in pores and fissures in the sediment, so it can indicate the intensity bio-pedogenesis quite well.These proxy indexes also reflect obvious regional difference of pedogenic environment and the intensity bio-pedogenesis; namely, secondary clay action, dissolving-leaching action and bio-pedogenesis are all much stronger in south than that in north.(2) There is stage of soil formation from the evolution of pedogenic environment in the Weihe valley during Holocene. Soil formation shows the law of evolving from warm and wet strong soil formation period to cold and dry dust deposition period (weak soil formation period) and to warm and wet strong soil formation period again. The loess-soil sequence is a compound soil sectional system of different kinds of soil evolution under different bio-environment andpedogenic processes. In the Weihe valley, the environmental effect of the summer monsoon on the south is much stronger than that on the north in the Holocene Megathermal, which is result forming deferent structure of paleosoil (So) at the MJY-A site and the WSC site: at the MJY-A she, the paleosoil (So) belongs to typical semiarid grasslands soil-Heilu soil with Apb-Ah-Bk-C soil sectional structure; at the MJY-A site, the paleosoil (So) belongs to typical semi7humid forest soil-brown soil with Ah-B1-Ck-C soil sectional structure.(3) Combining experimental data of environmental evolution with high resolution with historical data, it is showed that some coupling relationships exist between evolution of human culture and evolution of soil formation in the Weihe valley during Holocene. During 8 500-3 100 a B.P., with advantageous water, soil and organisms resources, the Dadiwan culture, the Yangshao culture, the Longshan culture and the Xiashang culture developed, original settling-down dry farming culture formed gradually, which laid sound foundation for agriculture civilization in the Weihe valley; Among which, land use of arable farming was replaced largely by pastoral farming in the mixed area of agriculture and animal husbandry in north Weihe region between 4 000-3 000 a B.P., because of dry and cold weather resulted in environment deterioration and soil degradation. At the beginning of 3 100 a B.P., as the climate has become dry, and dust storms and dust-fall occurred frequently in whole Weihe valley, the recent loess (L0) has begun to accumulate and gradually covered the mid-Holocene soil (S0). The change from soil formation to loess accumulation indicates environment deterioration and soil degradation. Degeneracy of water, soil and organism has shook the economic foundations of dry agriculture and nomadic industry and affected the social development of Xian Zhou and Western Zhou Dynasty.(4) With the range expanding an...
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