Summary
Holoence polycyclic soils were discovered on the Zhouyan tabeland. A typical
loess profile is observed by field and soil micromorphology, as well as magnetic susceptibility, grain size analysis and trace elements. Argillic horizons were identified in the soil and calcification was observed in the loess
layer in the profile. It suggests that the Holoence
palaeosols S 2 0 and S 1 0 were formed in
warm wet forest environment. Because of the deposition of a layer (L x) during the aridity interval between 6 000 and 5 000 aB.P., the palaeosols S 0, normally associated with the Holoence Megathermal period, is thus separated into two distinct soils, namely palaeosols S 2 0 and S 1 0. The conclusion is confirmed by the magnetic susceptibility, grain size and trace elements in the profile. It indicates that the lower soil (S 2 0) was formed in the warm wetest phase in the Holoence in the Guanzhong basin, with the strongest pedogensis, between 8 500 and 6 000 aB.P. The upper soil (S 1 0) was developed in another warm wet phase when the rainfall was probably lowered slightly between 5 000 and 3 100 aB.P. It has been a relative aridity period during the last 3 100 years, with accelerated aeolia dust deposit. A layer of 40～60 cm thick loess has been accumulated on the Zhouyuan tableland and thus the siol complex has been buried and becomes palaeosol of the Holoence.