水保所知识产出(1956---)知识库

【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 loess-paleosol 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 the aid 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 paleo-environment 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－montmorillonite－chlorite－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  illite － chlorite － 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.  ;黄土-古土壤序列是记录第四纪气候环境变化的良好信息载体之一。以黄土高原南缘陕西省淳化黄土-古土壤序列为研究对象，通过 X 射线衍射法对黄土-古土壤剖面上黏土矿物进行定性与半定量分析，调查不同土层黏土矿物相对含量及伊利石/绿泥石比值（I/C 值）的变化规律，并结合伊利石结晶度的变化特征，探讨不同土层黏土矿物特征所对应的气候变化规律，揭示黄土高原南部地区在更新世时期的气候环境演变规律。结果表明：（1）淳化剖面黏土矿物的相对含量、I/C 值以及伊利石结晶度 IC 值在反演古气候方面具有较好的指示性。（2）淳化剖面不同土层的黏土矿物类型基本相同，但其相对含量存在差异。在 WL-3～S5 阶段，即早更新世至中更新世中期，黏土矿物的组合类型为伊利石－蒙脱石－绿泥石－高岭石－蛭石，其中早更新世至中更新世早期（WL-3～L11 阶段），伊利石相对含量相对偏低，气候以温凉为主，而中更新世中期（S10～S5 阶段），伊利石相对含量上升，但蒙脱石、绿泥石含量均降低，气候相对温湿；在中更新世晚期（L5～S1 阶段），黏土矿物的组合类型改变为伊利石－绿泥石－蛭石－高岭石－蒙脱石，以伊利石和绿泥石为主，气候较为干冷。黏土矿物类型及含量表明淳化地区从早更新世早期到中更新世晚期气候环境总体干冷化，并经历了温凉－温湿－干冷的变化过程。（3）I/C 值以及伊利石结晶度 IC值从剖面底部到顶部均经历了由小到大再到小的过程，它们与黏土矿物的含量所反映的气候变化规律一致。本研究有助于探索黄土高原南部地区在更新世时期的气候环境变化，为全面了解更新世黄土高原不同地区第四纪气候环境演变提供依据。