新疆盐渍化土壤中黏土矿物演化特征及其对成土环境指示

Clay minerals are key-components in soil systems. Ionic environments have effect on the clay minerals transformation. Study on clay minerals at salt environment mainly focused on salt lake and wetland and was only simple identification of soil clay minerals。However,weathering and transformation of clay mineral of saline soil in arid region has not been reported at home and abroad. The research team has chose saline soil of Shihezi in Xinjiang to study clay minerals .The result showed the salt content of soil influenced on clay mineral components of clay fraction，but the mechanism was not clear. According to basic theories on the soil clay mineralogy, crystallography and structural chemistry, this project will select typical salinized soil in Xinjiang,(1)by using X-ray diffraction(XRD), electron microscopy analysis to study clay mineral assemblage and morphology characteristics under different salinity condition;(2)by using the Rietveld whole pattern fitting to discuss the relationship between type and content of the soil base ions and the microstructure change characteristics, such as cell parameters, aluminum isomorphous replacement and to understand clay mineral formation and transformation mechanism of the saline soil in arid region.(3)by analysing stability isotope 18O/16O and D/H ratio of the clay mineral and δ13C of soil secondary carbonate to interpret information about climate and environment change during soil forming-process and reveal the evolution characteristics of saline soil in xinjiang. Results of this research will be helpful to reasonable improvement and utilization of saline soil and to promote mineralogy theoretical study of salinized soil.

黏土矿物是土壤重要组成部分。国内外对含盐环境黏土矿物研究集中于盐湖和湿地，且多是对矿物类型简单鉴定，而对干旱区盐化土壤中黏土矿物的研究未见报道。课题组前期选择新疆北疆盐化土壤进行研究，表明盐分含量影响土壤黏土矿物，但影响机理尚不清楚。本项目以新疆典型盐化土壤为研究对象，根据黏土矿物学、晶体学和结构化学等基本理论，(1)采用X射线衍射、电镜分析，研究不同盐分条件土壤黏土矿物组合和形貌特征；(2)结合差示X-射线衍射图谱Rietveld全谱拟合法，探讨土壤盐基离子类型及含量与晶胞参数、铝同晶替代量等微结构变化特征关系，明确盐渍化土壤中黏土矿物转化机制；(3)并根据黏土矿物稳定性同位素18O/16O 和 D/H比例、土壤次生碳酸盐δ13C测定结果，解读盐化土壤形成过程中气候和环境演变信息，揭示新疆盐化土壤演化特点。研究结果将推进盐化土粘土矿物学理论研究，并为合理改良和利用盐化土壤提供科学依据。

在新疆准噶尔盆地和塔里木盆地采集不同盐化程度土壤，研究不同盐分条件下土壤黏土矿物组合特点、形貌特征；根据不同土层内黏土矿物中稳定性同位素18O/16O和D/H的比例和土壤次生碳酸盐中δ13C和δ18O同位素，解读新疆盐化土壤形成过程中气候和环境演变信息；并分析气候和土壤盐化程度对矿物形成和转换的影响，揭示新疆干旱区含盐环境中黏土矿物转化机制。结果表明准噶尔盆地盐渍化土壤中粘土矿物主要是伊利石，其次是蒙脱石、绿泥石，只有少量的高岭石；塔里木盆地盐渍化土壤中以伊利石为主、其次是绿泥石，少量高岭石，几乎没有蒙脱石。准噶尔盆地采样点盐渍化土壤中蒙脱石含量较高，且蒙脱石含量随着伊利石含量减少而增加，两者之间达到极显著负相关关系（r=0.80，n=49，p＜0.01），表明土壤中存在伊利石向蒙脱石的转化过程。一般认为伊蒙转化过程受水分条件的影响，需要伊利石脱钾、脱铝，Si进入，Ca2+和Na+取代伊利石层间K+。土壤次生碳酸盐δ13C、δ18O同位素和粘土矿物的D/H、δ18O同位素测定结果反映出准噶尔盆地气候相对塔里木盆地湿润。相对湿润气候条件下，准噶尔盆地土壤中伊利石发生脱K+，土壤溶液中大量Ca2+、Na+和Mg2+进入伊利石层间占据K+空位，盐渍化土壤pH＞8.5，使长石中的Si4+溶解，参与矿物转化过程形成蒙脱石。但准噶尔盆地盐渍化土壤剖面表层土壤次生碳酸盐中δ18O值明显高于下层土体，反映出该土层相对干旱，其水分条件表不利于伊利石脱K+，因而所有土壤剖面表土中蒙脱石含量都是最低的。10cm以下土层的相对湿润气候条件更利于伊利石向蒙脱石转化。10cm以下土体中，盐分的存在利于准噶尔盆地盐渍化土壤中伊利石向蒙脱石转换，土壤盐分含量与蒙脱石含量存在极显著负相关关系（r=0.61，n=40，p＜0.01）。塔里木盆地盐渍化土壤中矿物间没有明显的转换关系，主要是因为塔里木盆地气候相对准噶尔盆地更干旱。这种干旱气候使当地化学风化作用弱，以物理风化为主，土壤中没有明显的矿物转化过程。因此，气候和盐分含量是新疆两大盆地盐渍化土壤中粘土矿物形成和转化的主要影响因素。