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末次间冰期以来沙漠边缘黄土沉积的地球化学特征初探

期刊名称：沉积学报
时间：0
页码：543-547
语言：中文
分类：P593[天文地球—地球化学;天文地球—地质学] P931.6[天文地球—自然地理学]
作者机构：[1]华东师范大学资源与环境科学学院,上海200241, [2]兰州大学资源环境学院,兰州730000, [3]兰州大学西部环境与气候变化研究院,兰州730000
相关基金：国家自然科学青年基金项目（批准号：40801005）; 西部环境变化国家创新研究群体科学基金项目（批准号：40721061）资助
相关项目：13万年以来黄土高原西部地区黄土搬运、沉积和风化历史——地球化学研究

关键词：沙漠边缘, 黄土, 地球化学, 物质来源, desert margin, loess, geochemical indicators, material sources

中文摘要：

沙漠边缘地区黄土磁化率的增强机制与黄土高原地区有所不同,不宜用于夏季风强度变化的重建。所以,本文尝试将黄土高原地区常用的化学风化指标：化学蚀变指数（CIA）和Rb/Sr用于沙漠边缘地区白崖剖面夏季风演化的重建。结果显示,CIA可以较好地反映成壤作用,因而也可以较好地反映夏季风的变化,而Rb/Sr受源区因素和成壤因素共同作用,不能有效地指示夏季风的强度。同时,本文还选取了常见的反映粒度分选和冬季风变化的SiO2/TiO2和Zr/Rb,结果显示,SiO2/TiO2和Zr/Rb能明确指示粒度分选作用和冬季风的变化。此外,Al-Ti-Zr三角图显示,物源在不同时期存在一定的变化,在全新世和末次间冰期黄土物质混合较为均匀,表明风尘经历了较长距离的搬运和较为充分的混合过程;在末次冰期黄土物质混合程度存在明显分异,意味着部分时段物源可能较近。

英文摘要：

The loess deposition at desert margin holds a good archive of climatic change as such area is sensitive to variations of Asian Monsoon.However,due to the complexity of magnetic enhancement mechanism in loess at desert margin,magnetic susceptibility is not suitable for summer monsoon reconstruction.In this paper,we investigated the geochemical characteristics of loess deposition since last interglacial at desert margin and try to screen good geochemical indicators of weathering and sorting of loess deposition at desert margin.In doing so,we investigated a loess site at Baiya which is located 50 km south to Tengger Desert.The Baiya loess section in this study consists of S0,L1 and S1,corresponding to the Holocene,the last glacial,and the last interglacial respectively.730 samples were collected from this section.All of them were subjected to magnetic measurement using Bartington MS2B and grain size analysis using Malvern Mastersizer 2000.183 samples were subjected to chemical elements determination using X-ray fluorescence（XRF） analysis on Panalytical Magix PW2403 spectroscope.All the lab works were carried out at the Key Laboratory of Western China＇s Environmental Systems（Ministry of Education）,Lanzhou University. The geochemical results from the whole section show that the content of SiO2,Al2O3 is close to that of UCC,the content of CaO,MgO,TiO2,Fe2O3 was enriched relative to that of UCC;the content of Na2O,K2O was depleted relative to that of UCC.As the chemical weathering strengthened,the striking phenomenon of elements behavior of this section is the depletion of sodium and the enrichment of iron and magnesium.However,the behavior of calcium was equivocal,which is probably caused by weak leaching in deposition area and strong evaporating-induced ascending of Ca in source area.Generally,the chemical weathering in the study area is weak and on its initial weathering stage as expressed by the low chemical index of alteration（CIA） which spanned from 50 to 60. Four frequently-used geochemical indicato