内蒙古中部第四纪沉积物中黏土矿物组合特征与古天气演化关系.doc

内蒙古中部第四纪沉积物中黏土矿物组合特征与古天气演化关系 【中文摘要】黏土矿物普遍存在于各种类型的沉积物中。作为次生矿物,黏土对环境的变化极为敏感,因而粘土矿物的沉积分异、成分及组合特征、矿物的结晶度及稳定同位素等,都从不同的角度记录了黏土矿物的形成过程中各种环境因素的变化。又由于黏土矿物分布的广泛性和取样的简易性存在于地表和近地表,使黏土矿物成为古天气研究的有效手段之一。本文选择内蒙古中部四子王旗地区作为研究区域,在区域填图及重点剖面分析基础上,建立起了该区第四纪以来相对完整的地层层序。采用X射线衍射分析方法,对代表性剖面沉积物样品中的黏土矿物成分以及质量分数进行了测定。结果表明,工作区南部大庙地区第四纪早中更新世沉积物中,大量出现高质量分数的伊蒙混层和蒙脱石,高岭石与绿泥石含量很少,说明该区当时处于中纬度季节性冷热、干湿交替的古环境天气中。而工作区北部的呼和诺尔南岸地区晚更新世地层中,伊蒙混层含量较高,不再出现蒙脱石,天气变化已趋于稳定,但伊利石含量增加较为明显,表明降雨量减少,化学淋滤作用减弱,水解作用降低,机械风化作用增强。同时,湖相地层中出现晶形完整的石膏晶体,说明该区在这一时期内天气变冷且转为干旱。在呼和诺尔北岸地区全新世地层中,伊蒙混层矿物质量分数明显降低,高岭石、伊利石和绿泥石含量均有所增加,表明该时间段内化学淋滤作用仍然较弱,降雨量继续减少。总体而言,本区的古天气在第四纪经历了由干湿交替到温凉偏干的过程。岩石地层、地貌特点、古生物化石组合等所反映的古天气特征及其变化,均与当前黏土矿物的分析基本吻合。通过资料对比,本区第四纪以来天气特征与整个中国东部第四纪天气变化大趋势基本一致。这说明黏土矿物分析方法在本区的古天气研究当中确实是可行的。; 【Abstract】 Clay minerals can be found in various sediments. As the secondary minerals originated from the sedimentary process, they are highly sensitive to the sedimentary environmental changes. The characteristics of clay minerals, such as the sedimentary differentiation, the compositions and their assemblages, the crystallinity index, as well as the stable isotopes and so on, could be the implicative records of the environmental changes during the clay minerals ation.On the basis of the systematic mapping work and the further observation at the typical outcrop sections, combining with the previous data, a relative complete regional Quaternary stratigraphic framework of the Siziwangqi, central Inner Mongolia, has been established preliminarily. To recognize the compositions and quantity of the clay minerals, all the samples from the typical sections have been analyzed with the powder X-ray diffraction XRD techniques. All the samples of the early-mid Pleistocene sediments from the Damiao Town of Siziwangqi, which is located in the south part of the study area, consist of abundant mixed-layered illite/smectite I/S and smectite, but few kaolinite and chlorite. It suggests that this region should be a kind of temperate monsoon climate in the mediate latitude with evident alternative of dry and humid characters during this period.Those of the late Pleistocene sediments at the south bank of the Huhnor Lake of Siziwangqi, which is located in the north part of the study area, contain abundant mixed-layered illite/smectite I/S and lack of smectite. It suggests that the climate should not be changed severely during this period. In addition, because of the increasing illite in the sediments, it indicates the decreasing of rainfall that resulted in the weakening of the chemical eluviations and the hydrolization, and the enhancing of the mechanical-weathering. Moreover, the lacustrine gypsum and other saline deposits indicate that the climate had been changed into colder and drier.In the Holocene sediments at the north bank of the Huhnor Lake, the contents of the mixed-layered illite/smectite I/S decreased while those of the kaolinite, chlorite and illite had been increased. It probably suggests that it should be lack of the rainfall weakening the chemical eluviations during this period.According to the analyses of the clay minerals of the related sediments, during the Quaternary, the climate of the central Inner Mongolia should be developed from the dry to the humid alternately in the early-mid Pleistocene, then to temperate cool with slightly dry in the late Pleistocene and Holocene. Further, the characteristics of the litho-facies, lands, as well as the fossils faunas are in good agreement with the present paleoclimate study based on the clay minerals analyses. In general, the evolutionary process of the Quaternary climate in the central Inner Mongolia is consistent with the tendency of the whole east China during the same period. Consequently, it may suggest that the present paleoclimate study based on the clay minerals analyses is reasonable and operable.