海拔与岩性变异对石灰岩发育土壤黏土矿物组成的影响

摘要

用X射线衍射法研究了中亚热带区海拔、岩性变异对石灰岩发育土壤黏土矿物组成的影响.结果表明:在海拔约2 000 m的重庆金佛山山顶区,灰黑色钙质页岩石灰岩发育的黑色石灰土,矿物组成复杂,除伊利石为主外,还有少量蛭石、绿泥石、高岭石和蒙脱石,有一定量的母质残留矿物(滑石和滑间皂石);由砂页岩和灰岩互层母质发育的山地黄棕壤,以蛭石为主,伊利石和高岭石其次,有三水铝石和弱结晶针铁矿.在金佛山中下部(600～1 200 m),石灰岩发育的黄色石灰土以蛭石或伊利石为主,有一定量的高岭石,普遍出现针铁矿.湖南怀化盆地海拔200多米,纯灰岩发育的红色石灰土为伊利石、蛭石和高岭石(含埃洛石)组合型,有结晶好的针铁矿和少量赤铁矿.海拔显著影响高岭石含量、针铁矿结晶度,海拔降低时高岭石含量增加,针铁矿结晶度提高.在金佛山山顶区,石灰岩母质岩性和微地形变异对土壤成土过程和黏土矿物组成影响显著.%The purpose of this paper is to determine the effects of elevation and lithology on clay mineral composition of soils derived from limestone in south China.The research areas were located in the Jinfo Mountain,Chongqing municipality,and the Huaihua Basin,Hunan Province,two karst regions.The samples of Black limestone soil (Jf07) and the Mountain yellow-brown earth (Jf12) were collected on the top of the Jinfo Mountain,about 2 000 m in elevation;the samples of Yellow limestone soils (Jf02,Jf20 and Jf23) on the mid-and lower-slopes of the Jinfo Mountain,about 600 ～ 1 200 m in elevation;the sample of Red limestone soil (Hh01) in the Huaihua Basin,Hunan Province,over 200 m in elevation.Soil mineralogy of the samples was determined by X-ray diffraction (XRD) on the ＜ 1 μtm (clay) fraction in B horizons.Results show,in the mid-subtropical zone of China,clay minerals in the limestone soils are dominated mainly with 2:1-typed illite or vermiculite,in addition to some 1 ∶ 1-typed kaolinite and halloysite.With elevation going downwards,the fractions of kaolinite and goethite in soils exhibit a trend of increase,and their crystallinity increase too;this shows that,with the locations descending on slope,the soils are intensifying in weathering.On top of the Jinfo Mountain,lithology,topographic feature and vegetation are important factors,affecting soil forming process and mineral composition of the clay.On top of the Jinfo Mountain,the Permian Maokou Formation is a set of stratum of limestone larded with grey-dark carbonaceous shale;the Permian Longtan Formation is a set of interbedded rocks of limestone and sandstone-shale.Due to being significantly affected by the Permian Maokou Formation,Jf07 soil is weak in weathering,its clay mineral composition is complicated;there are certain amounts of talc and aliettite,which are residues from its grey dark parent rocks.But,Jf12 soil is well-developed,its clay mineral composition is simple,and its main clay mineral is vermiculite;this is attributed to the impact of the parent rock (Permian Longtan Formation).