干旱区生态环境知识资源中心(Arid): 伊犁典型黄土磁学与常量元素地球化学特征及其古气候意义

Arid

	伊犁典型黄土磁学与常量元素地球化学特征及其古气候意义
其他题名	ROCK MAGNETISM AND GEOCHEMICAL CHARACTERISTICS OF MAJOR ELEMENTS OF TYPICAL LOESSS IN THE ILY BASIN AND THEIR PALEOCLIMATIC SIGNIFICANCE
	陈渠; 吕镔; 刘秀铭; 叶玮; 赵国永
来源期刊	第四纪研究
ISSN	1001-7410
出版年	2021
卷号	41 期号:6 页码:1632-1644
中文摘要	选取有多层古土壤发育的新疆伊犁尼勒克黄土剖面,分析其地球化学特征与粒度分布,并做详细的岩石磁学研究,检测磁性矿物组成和亚铁磁性矿物粒度在各黄土-古土壤层的变化,探讨其记录的古气候演变过程。常量元素地球化学元素测试结果显示:尼勒克剖面MgO、Na_2O与CaO在剖面下部变幅较大,在最底部的S3古土壤层含量低;各常量元素含量与伊犁的波马剖面和塔勒德剖面一致,普遍低于天山北麓黄土;元素含量比值风化指标显示古土壤层化学风化程度较高,其中又以S_3最高;Fe_2O_3/Al_2O_3在古土壤层较高,反映化学风化过程中铁相对富集。剖面磁性强弱的垂向变化主要受控于风成输入的磁铁矿。就整个剖面而言,成壤生成的超细颗粒亚铁磁性矿物相对含量随深度减少呈降低的趋势,在古土壤层比在黄土层更高;亚铁磁性矿物的粒度在S_3最细,较多分布在超顺磁至稳定单畴的粒径范围之内。各黄土-古土壤层样品热磁曲线变化都受磁铁矿主导,L_3热磁曲线有别于L_1和L_2,而与S2相似。<4 m粒度组分的磁性矿物组成并不像较粗组分一样以磁铁矿为主,而是含有较多赤铁矿,反映过湿条件下成壤产生的磁赤铁矿转化为赤铁矿,不同于黄土高原的成壤过程生成大量磁赤铁矿的磁性成壤增强模式。尼勒克黄土地球化学、粒度与环境磁学指标一致揭示自S_3发育以来至全新世古气候干旱化的趋势。综合各指标变化与热磁曲线差异,研究区古气候演变可以分为两个阶段,即S_3发育至L_2堆积之前阶段与L_2堆积以来至全新世阶段,在S_2/L_2过渡时期干旱化突然加剧。虽然伊犁黄土不同剖面的磁学性质不同,但都反映了干旱化的趋势。
英文摘要	The Ily basin is located in Central Asia. Due to the geographic situation, the climate in the Ily basin is dominated by the westerlies and varies between low lands and mountain areas. The average annual precipitation within basin can be as high as 850 mm. Loess is widely distributed, extending from the slopes of the Tianshan Mountains to the edge of the deserts. There are outcrop loess profiles on the river terraces of the upper and middle reaches of the Ili River and its tributaries. It is generally believed that the loess in the Ily basin origins from deserts in Central Asia. However, recent studies suggest that local sources can contribute significantly to loess forming. In an arid climate at low altitude,the paleosols are generally not developed and show little difference from loess units, while in the eastern Ily basin with higher precipitation,loess deposits show relatively strong pedogenesis and clear distinction between loess-paleosol units. Since it is located to the east of the deserts and sensitive to the changes in the westerlies, its paleoclimatic significance has drawn much attention in the past several decades. Although much research work has been done using approaches such as grain size, geochemistry, chroma characteristics and rock magnetism,there have been few detailed studies using multiple approaches. Apart from the report on the Talede section at Xinyuan County, there have been little studies on the paleoclimatic reconstruction by loess records that spans more than one glacial-interglacial cycle. A 29.7 m-thick typical loess section at Nileke County ( 43°39.4'N, 82°44.8'E; 1237 m a. s. 1.) is selected for the preset study. The topmost 0.5 m are Holocene soils ( S_0 ). In correlation to the Chinese Loess Plateau, the paleosol units of S_1,S_2 and S_3 were designated to the depth intervals at 3 ~ 6 m, 17.0 ~19.3 m and 24.0 ~29.7 m respectively, and the loess units of L_1,L_2 and L_3 to the interbeded layers. The paleosols distinguish from the loess units by red color and fine texture, with S_3 noticeably more developed. 594 samples were collected in total at an interval of 5 cm,and subjected to granulometric analysis and rock magnetic measurement. Besides routine magnetic measurement, hysteresis loop measurement and thermomagnetic (J-T) analyses using a Variable Field Translational Balance( VFTB),temperature dependant susceptibility (kappa-T) measurement using a Kappabridge MFK 1-FA ( AGICO ),and low temperature demagnetization measurement was performed on selected samples. The pipette method was used on selected samples to yield three particle-sized fractions(< 4 m,4 ~ 16 m, 16 ~63 m and >63 m ). The CBD method was used to dissolve the fine-grained minerals and collect a coarse fraction. The fractions attained by using both methods were also subjected to rock magnetic measurement for comparison. Typical samples from the paleosol-loess sequence were selected for geochemical analysis. Approximately 4 g of ground loess was mixed with 6 g of Li_2B_4O_7 and tested for major element concentrations using an ARL PERFORM ' X X-ray fluorescence spectrometer. Multiple proxies show consistent variations with depth at the Neleke section. The grain size distribution suggests that the loess is of aeolian origin. The >63 m fraction is generally < 5% even in the loess units, which is indicative of the insignificance of proximal sources. The grain size parameters demonstrate conspicuous variations between the loess and paleosols and distinction between the lower part( 17.0 ~29.7 m,S_2 and below) and the upper part(0~17 m,L_2 and above). The geochemical composition of the Nileke section is similar to that of the Boma section ( at Zhaosu county) and Talede section (at Xinyuan county) in the Ily basin. Major element (Si, Al, Fe, K,Na, Ca, and Mg) concentrations are relatively constant in L, and S_1,but fluctuate below S_1. Geochemical proxies show higher weathering intensity in S3 than in the other layers.
中文关键词	黄土 ; 古土壤 ; 伊犁 ; 古气候 ; 环境磁学 ; 地球化学 ; 粒度
英文关键词	loess paleosol Ily Basin paleoclimate environmental magnetism geochemistry grain size
类型	Article
语种	中文
收录类别	CSCD
WOS类目	Geology
CSCD记录号	CSCD:7087930
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/377593
作者单位	陈渠, 浙江师范大学地理与环境科学学院, 金华, 浙江 321004, 中国.; 叶玮, 浙江师范大学地理与环境科学学院, 金华, 浙江 321004, 中国.; 吕镔, 福建师范大学地理研究所;;福建省湿润亚热带山地生态重点实验室省部共建国家重点实验室培育基地, ;;福建省湿润亚热带山地生态重点实验室省部共建国家重点实验室培育基地, 福州;;福州, 福建;;福建 350007;;350007, 中国.; 刘秀铭, 福建师范大学地理研究所;;福建省湿润亚热带山地生态重点实验室省部共建国家重点实验室培育基地;;Department of Earth and Environmental Sciences,Macquarie University, ;;福建省湿润亚热带山地生态重点实验室省部共建国家重点实验室培育基地;;, 福州;;福州;;Sydney NSW, 福建;;福建;;Australia 350007;;350007;;2109, 中国.; 赵国永, 信阳师范学院地理科学学院, 信阳, 河南 464000, 中国.
推荐引用方式 GB/T 7714	陈渠,吕镔,刘秀铭,等. 伊犁典型黄土磁学与常量元素地球化学特征及其古气候意义[J],2021,41(6):1632-1644.
APA	陈渠,吕镔,刘秀铭,叶玮,&赵国永.(2021).伊犁典型黄土磁学与常量元素地球化学特征及其古气候意义.第四纪研究,41(6),1632-1644.
MLA	陈渠,et al."伊犁典型黄土磁学与常量元素地球化学特征及其古气候意义".第四纪研究 41.6(2021):1632-1644.