Paleosol evolution and environmental change in the Huang-Huai-Hai Plain, China

Paleosols in the Huang-Huai-Hai Plain occur mainly in the Huaibei, Xuhuai, Yischuhe and Jiaolai areas. They result from 3 sedimentation-soil formation cycles since the Late Pleistocene. Each cycle left calcareous concretions, a dark soil horizon, and a topsoil horizon and/or a stratified soil horizon all derived from loess. This paper examines the composition of the concretions, compares this with that of the enclosing soil horizons, and draws some environmental conclusions. Three types occur: embryonic calcareous concretions, mature calcareous concretions, and calcareous hardpans (petrocalcic horizons). The embryonic concretions formed during the mid-Holocene (6780±130 yr. B.P.), mature calcareous concretions during the late-Pleistocene (weighted average of 31 samples = 15670±370 yr. B.P.), and calcareous hardpans (petrocalcic horizons) from 16 to 40 ka B.P. The calcium carbonate content increases from 412 g/kg in the embryonic concretions, to 551 g/kg in the mature concretions, and to 691 g/kg in the hardpan, whereas contents of SiO_2, Al_2O_3 and TiO_2 decrease accordingly. Spore pollen analysis shows that the late-Pleistocene there was dry and cool, whereas the mid-Holocene was warm and humid and lakes were more extensive than today.