Friday, 14 July 2006

Polygenetic Soils and Environmental Changes in the Northern Subtropical Region of China.

Ke-ning WU, Department of Land Science and Technology, China University of Geoscience, 29,Xueyuan Road , Haidian Dist, Bejing, 100083, China

Polygenetic soil profile is located at about 15 km to the south of Fangcheng county, Henan province, near the northern margin of the Nanyang basin in the subtropical region of China.The soil profile being made up of four different soils, total thickness is 1000cm.The upper part is Holocene lake sediment black clay,consisting of three layers. 0-28cm plow horizon is grayish brown(7.5YR6/2)dry, The second layer 28-89cm is black brown (10YR2/3)dry, showing evidence of shrink-swell activity, including slicken sides, angular blocky or wedge-shaped structural aggregates and cracks and appearing to have vertic activity or pedoturbation. This horizon contains a high content of iron manganese concretions. The clay is mainly montmorillonites. The third layer 89-191cm is a petrocalcic horizon with calcium carbonate concretious (shajiang in chinese).IRSL Dating Date (a.B.P.)11.81.5 ka. Paleovegetation is warm temperate zone marsh and meadow. Soil classification is Shajiang black soil ,Calcic udic Vertisols(CSTS1995), Calcic Vertisols(FAO1998), Hapluderts (ST1999).The second part is Xiashu Loess of late Pleistocene, It consist of four layers, 191-305cm,305-365cm,365-435cm and 435-625cm.The soil color is mainly yellow orange(10YR8/8) and bright yellowish brown(10YR7/6)dry , The horizons have prismatic structure, clay films on ped surfaces and iron-manganese concretions. Oriented clay in the form void and channel argillans can be observed in the thin section. The formation of the argillic horizon involved both residual and illuvial processes. Clay mineralogy is mainly hydromica, kaolinite and vermiculite.IRSL Dating Date (a.B.P.)109.813.7ka.Paleovegetation is Subtropical zone coniferous-broad leaved mixed forest steppe. Soil classification is yellow brown soil ,Ferric udic Luvisols(CSTS1995), Ferric Luvisols (FAO1998),Ferrudlalfs(ST1999).The third part is river alluvium, consisting two layers, 625-795cm yellow (2.5Y8/6)dry, The thickness is about 170cm, has distinct stratification and no clay films. 795-805cm horizon is yellow orange(7.5YR7/8)dry, with a high content of 1-3mm gravels. .IRSL Dating Date (a.B.P.)133.717.9ka. Soil classification is Alluvial soil ,Eutric Fluvisols(CSTS1995), Eutric Fluvisols (FAO1998),Udifluvents(ST1999).The fourth part is paleosoilo Lishi Loess ,from the middle Pleistocene. It consisting three layers,805-855cm and 855-965cm horizons are orange(7.5YR7/6)dry, have prismatic structure,with many ferran-humic clay films on ped surfaces,and oriented argillans in voids and channels, deceasing with depth. Clay mineralogy is mainly hydromica, vermiculite. and montmorillonites. IRSL Dating Date (a.B.P.)149.820.3ka.Last layer more than 965cm, IRSL Dating Date (a.B.P.)154.113.6ka. Paleovegetation is temperate zone evergreen broad-leaved and decidous- broad leaved mixed forest. Soil classification is Brown soil , Ferric udic Luvisols(CSTS1995), Chromic Luvisols (FAO1998),Ferrudlalfs(ST1999).

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