刘昌,
徐海伟,
刘成英^,
兰州大学地质科学与矿产资源学院, 甘肃省西部矿产资源重点实验室, 兰州 730000

基金项目: 科技部第二次青藏高原综合科学考察研究项目（2019QZKK0704）和甘肃省科技计划项目（20JR5RA260）资助


详细信息

作者简介: 刘昌, 男, 1995年生, 硕士研究生, 矿物学、岩石学、矿床学专业, 研究方向为环境磁学.E-mail: chliu2018@lzu.edu.cn

通讯作者: 刘成英, 女, 博士, 讲师, 主要从事古地磁学和岩石磁学研究.E-mail: cyliu@lzu.edu.cn

中图分类号: P318

收稿日期:2020-11-05
修回日期:2021-04-09
上线日期:2021-06-10

Mineral magnetic characteristics of 2018 flood sediments in the upper reaches of the Yellow River and its implication for paleoflood reconstruction

LIU Chang,
XU HaiWei,
LIU ChengYing^,
Key Laboratory of Mineral Resources in Western China(Gansu Province), School of Earth Sciences, Lanzhou University, Lanzhou 730000, China



More Information

Corresponding author: LIU ChengYing,E-mail:cyliu@lzu.edu.cn

MSC: P318

--> Received Date: 05 November 2020
Revised Date: 09 April 2021
Available Online: 10 June 2021


摘要
摘要:现代洪水沉积物的沉积学特征研究是开展古洪水重建的一项基础工作.2018年黄河汛期洪水沉积物在兰州体育公园形成了一道天然堤.对该天然堤剖面的岩石磁学研究显示：沉积物中的磁性矿物既有磁铁矿，又有赤铁矿/针铁矿.磁化率、饱和等温剩磁、非磁滞剩磁、S-ratio和L-ratio等参数在剖面上没有明显变化，指示2018年洪水沉积物源区、磁性矿物的种类和含量变化不显著.剖面下部（66~110 cm）沉积物的磁化率各向异性（AMS）椭球最大轴偏角集中分布（K₁-Dec=22.8°±10.3°），上部（0~64 cm）沉积物的磁化率最大轴偏角在上半平面内随机分布；下部沉积物的磁性矿物粒度指标（χ_ARM/χ和χ_ARM/SIRM）和天然剩磁（NRM）强度低于上部；指示洪水沉积物的下部和上部分别形成于2018年黄河二号和三号洪水期间.由于二号洪水流量及水位陡升陡降、持续时间短，三号洪水水位升降相对缓慢、持续时间长；造成了两次洪水沉积物的AMS特征、χ_ARM/χ、χ_ARM/SIRM以及NRM强度差异.本研究揭示洪水沉积物的磁学参数能够灵敏地响应不同水动力条件和持续时间的洪水期次，从而具有高分辨率区分洪水事件的潜力.
关键词: 黄河/
洪水沉积物/
磁化率各向异性/
磁学参数/
天然剩磁强度

Abstract:Establishing characteristics of modern flood sediments is essential to reconstruction of paleoflood events. This study focuses on a natural levee in Lanzhou Sports Park which was formed in 2018 Yellow River flood season. Rock magnetic investigations demonstrate that the magnetic minerals in the flood sediments are mixtures of magnetite and hematite/goethite. Some magnetic parameters, such as magnetic susceptibility(χ), saturation isothermal remanent magnetization(SIRM), anhysteretic remanent magnetization(ARM), S-ratio and L-ratio display insignificant changes with depth, suggesting that minor changes in origin and concentration of magnetic minerals of the flood sediments. Some other magnetic parameters, however, such as anisotropy of magnetic susceptibility(AMS), χ_ARM/χ, χ_ARM/SIRM, and natural remanent magnetization (NRM) intensity display distinct two different stages. In the lower part (66~110 cm), the declinations of the maximum principal susceptibility (K₁-Dec) are clustered around 22.8° (±10.3°), whereas, K₁-Decs are highly dispersed in the upper part (0~64 cm). In addition, values of χ_ARM/χ, χ_ARM/SIRM and NRM intensity in the lower part are less than those in the upper part. These clues suggest that the lower and upper part of the flood sediments were formed during the Yellow River Flood No.2 and No.3 in 2018, respectively. Compare to steep water level fluctuation and short duration(one day) of flood No.2, the No.3 flood is typical of relatively slow water level changes with longer (two week) duration. The distinct hydrodynamic conditions and duration of No.2 and 3 floods are responsible to the differences of magnetic parameters from upper and lower parts. Therefore, this study reveals that magnetic parameters are sensitive to different hydrodynamic conditions and duration of flood that are potential to distinguish the paleoflood events with high resolution.
Key words:Yellow River/
Flood sediment/
Anisotropy of magnetic susceptibility/
Mineral magnetism/
Natural remanent magnetization



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