三门峡地区黄土-古土壤序列物源分析与环境意义

Provenance Analysis and Environmental Significance of Loess-Paleosol Sequences in the Sanmenxia Area

三门峡地区位于黄土高原东南缘,是东亚季风影响的黄土沉积敏感地区,对研究东亚季风演化、环境演变有重要意义,目前对该地区多采样传统的研究方法,存在较大争议。端元分析能够分解沉积过程中沉积物不同来源的粒度组分,据此对黄土高原东南缘三门峡地区马坡剖面10 m风成黄土—古土壤序列进行粒度端元分析,同时引入沉积年代接近的黄土高原西北部会宁剖面2.3 m的黄土—古土壤序列粒度端元特征进行对比验证,两者都分解出3个代表不同沉积特征的端元。通过区域对比表明:3个端元能够指示三门峡地区黄土物质来源的3个组分,马坡剖面EM1端元属于黏粒和细粉过渡组分,代表东亚夏季风影响下的成壤作用;EM2属于细粉砂组分,代表高空西风远源搬运的风成沉积物;EM3属于粗粉砂组分,代表东亚冬季风低空跃移输送组分。同时,结合各端元组分含量与磁学参数、中值粒径等指标,表明端元分析方法在这一地区是准确有效的,能够指示沉积过程中区域的气候变化特点。

Sanmenxia area is located in the southeastern edge of the Chinses Loess Plateau,which is a sensitive area of loess deposition influenced by the East Asian monsoon,and is of great significance to the study of East Asian monsoon evolution and environmental evolution.The End-member analysis can decompose the grain-size components of different sources of sediments in the depositional process.Our research focuses on the grain-size End-member analysis of the 10m wind-formed loess-palaeosol sequence of the Mapo section in the Sanmenxia area and the southeastern edge of the Loess Plateau.At the same time,the grain-size End-member characteristic of the loess-palaeosol sequence of the Huining section of the northwest Loess Plateau is introduced,which is close to the age of deposition.For the comparison and verification,both decomposed three End-members representing the different depositional characteristics.The regional comparison reveals that the three End-members can indicate the three components of loess material sources in the Sanmenxia area.The EM1 of the Mapo section belongs to the clay and fine silt overgrowth component,which represents the loam-forming under the influence of the summer winds of East Asia;EM2 belongs to the fine silt component,which represents the wind-formed sediments transported by the distant sources of the high-altitude westerly winds;EM3 belongs to the coarse silt component,which represents the low-altitude leap transport component of the winter winds of East Asia.Meanwhile,the combination of the content of each endmember component with the magnetic parameters,median grain size and other indicators shows that the endmember analysis method is accurate and effective in this area,and can indicate the regional climate change characteristics during the deposition process.