湘赣浙紫色土的类型与分布特点

湘赣浙紫色土主要分布在沅江、湘江、赣江、信江、衢江流域几个NE或NNE向平行排列的紫色丘陵盆地内,出露上白垩统一下第三系红色碎屑岩,可见中丘中谷、低丘宽谷和缓丘带坝三类地形,分布不同风化程度的成土风化壳和紫色土类型。三省酸性紫色土和中性紫色土比例较大,达73％,比四川盆地多38—39％。

CHARACTERISTICS OF TYPE AND DISTRIBUTION OF PURPLE SOILS IN HUNAN,JIANGXI AND ZHEJIANG PROVINCES

Purple soils in these provinces is mainly distributed on purple hills and basins, which are fromed by land of low hollow being parallelly arranged by NE or NNE in the basins of the Yuanjiang, Xiangjiang, Gangjiang, Xingjiang and Qujiang Rivers on the south of Changjiang River. Red clastic rocks of upper Cretaceons series-lower Tertiary system(K2-E) are mainly appeared in these regions. The altitude of the basins in west is higher,for example,there are many middle hills and middle valleys in Luxi County, Hunan Province, and the altitude of the red stratum hills is 150-300m;the altitude of the basins in east is lower,for example,there are many low hills and wide valleys and low hills with plain in Ji'an Municipality,Jiangxi Province, and the altitude of red stratum hills is 60-80m. On different landform,the weathering degree of original soil crust is different.On middle hills an middle valleys,the relative height is 15-45m,there mainly distributes weathering crust of original color thin layer clastic rock, the thickness is < 50cm, they generally form neutral and clacareous purple soils. On low hills and wide valleys, relative height is 5-15m,there mainly distributes weathering crust of original color clastic rock form thin to middle layer,the thickness is <80cm,there generally is not free carbonate,which mainly develop acid and neutral purple soils. On low hills with plain,the relative height is 3-5m,"covering cap "or "covering layer "appear on the tops of most hills. They may be red clay and sand-gravel layer of middle or upper Pleistocene series (Q2 or Q3),or plinthitic horizon or red weathering crust. According to the degree of weathering,they can develop red soils,sub-red soils and acid purple soils.Under the same standard,purple soils in Hunan,Jiangxi and Zhejiang Provinces are divided into calcareous, neutral and acid purple soils, but the classific standards of soil genus are different, their rule and soil nomenclature are different too.