| 其他摘要 | 【Objective】The loess-paleosol sequence on the Loess Plateau of China has been
considered as an important information carrier recording changes in the global environment and climate
of the Quaternary peroid. As weathering products of land surface, clay minerals are widely found in
Quaternary sediments, and their paleoenviromental significance has also attracted more and more attention.
It has been documented that the formation and transformation of clay minerals is closely related to climatic
conditions. However, so far, few studies have been reported on characteristics of the clay mineral in loesspaleosol
profiles in the southern part of the Loess Plateau. Besides, previous researches about paleoclimate
evolution in the south Loess Plateau focused mainly on Holocene, with little attention to climate changes
in the Pleistocene. 【Method】 In this paper, a typical loess-paleosol profile of the Loess Plateau was
selected in Chunhua County, Shaanxi Province, south of the Loess Plateau as research object. With theaid of the X-ray diffraction method, qualitative and semi-quantitative analyses of the soil samples from
different layers of the Chunhua loess-paleosol profile were carried out for analyzing relative contents of
clay minerals, illite/chlorite ratio (I/C value) and illite crystallinity (IC value), as well as regularities of
their evolutions, and further for relationships of the characteristics of the clay minerals in the profile with
changes in paleoclimate and eventually, for regularities of the evolution of the paleoclimate and paleoenvironment
in the Pleistocene in the south Loess Plateau. 【Result】Results show: (1) The three indices,
i.e. relative content of clay minerals, ratio of illite to chlorite (I/C values) and illite crystallinity (IC value)
of the Chunhua loess-paleosol profile are good indicators to be used in reversion of paleoclimate changes in
the Pleistocene. (2) All the soil layers of the profile had the same clay minerals, but relative contents of the
clay minerals varied significantly from layer to layer. During the period from the early Pleistocene to the
mid-middle Pleistocene (WL-3～S5), the clay minerals were composed mainly of illite－montmorillonitechlorite－
kaolinite－vermiculite, and this period could be divided into two stages according to the changes
in relative contents of the clay minerals. From the early Pleistocene to the early middle Pleistocene (WL-
3～L11), the relative content of illite was comparatively low while the relative content of chlorite was quite
high, which indicates that a cool temperate climate prevailed in this period. However, in the mid-middle
Pleistocene ( S10～S5), the relative content of illite increased, while the relative content of montmorillonite
and chlorite decreased, which indicates that the climate was relatively warmer and more humid in this
period. In the late middle Pleistocene (L5～S1), the composition of clay minerals turned to be of illitechlorite－
vermiculite－kaolinite－montmorillonite, and the relative contents of illite and chlorite increased,
implying a dry-cold climate dominated this period. Therefore, the changes in relative contents of the clay
minerals in the Chunhua loess-paleosol profile indicate that from the early Pleistocene to the late middle
Pleistocene, the climate generally became dry and cold, and experienced changes from cool temperate to
warm wet and to cold dry. (3) The ratio of illite to chlorite (I/C value) and illite crystallinity (IC value)
also exhibited phased variations from the bottom to the top of the Chunhua profile, that is increasing
first and then decreasing. The distribution of I/C ratio and illite crystallinity indicates that the climate in
the Pleistocene underwent an evolution process similar to that of the clay minerals in relative content.
【Conclusion】All the findings in this research are found to be conductive to the exploration of changes in
the climate and environment of the south loess-paleosol during the Pleistocene, and may serve a scientific
basis for comprehensive exploration of changes in climate and environment of various regions of the Loess
Plateau during the Quaternary period of the Pleistocene. |
; 黄菁华1,2; 姚军4; 胡斐南1,2; 霍娜4
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