Characteristics Of Clay Mineral Compositions Of Quaternary Deposits In Central Inner Mongolia: Implications For Quaternary Climate Change

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 formation.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, landforms, 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.