颜燕燕^1,,
张家富¹,
胡钢²,
周力平¹
1. 北京大学城市与环境学院, 地表过程分析与模拟教育部重点实验室, 北京 100871
2. 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029

基金项目: 国家自然科学基金项目（批准号：41471003）资助


详细信息

作者简介: 颜燕燕, 女, 26岁, 硕士研究生, 第四纪地质学专业, E-mail:yyyan0226@163.com

中图分类号: P597⁺.3

收稿日期:2018-01-27
修回日期:2018-03-15
刊出日期:2018-05-30

Comparison of various luminescence dating procedures on sediments from one of the strath terraces of the Yellow River in the Jinshaan Canyon

Yan Yanyan^1,,
Zhang Jiafu¹,
Hu Gang²,
Zhou Liping¹
1. Laboratory for Earth Surface Processes, Ministry of Education, College of Urban and Environmental Sciences, Peking University, Beijing 100871
2. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029


MSC: P597⁺.3

--> Received Date: 27 January 2018
Revised Date: 15 March 2018
Publish Date: 30 May 2018


摘要
摘要:黄河的系列阶地是其发育过程中最直接的遗迹记录，确定阶地的精确形成年代是研究其地貌演化最重要的关键问题之一。尽管以往对黄河阶地进行了大量的测年研究，尤其是光释光测年，但对各测年方法结果可靠性的比较相对较少。本研究选择黄河晋陕峡谷黑峪口地区的一个典型基座阶地，对其沉积物进行多方法的光释光测年研究，包括应用于细粒（FG）石英与粗粒（CG）石英的单片剂量再生法（OSL-SAR）和应用于粗粒钾长石的红外后多步高温红外法（MET-pIRIR）；同时，测定了现代黄河河流样品不同释光信号的残余剂量。结果表明，粗粒和细粒石英具有不同的光释光性质，细粒石英的光释光性质具有更多的快组分、更高的饱和剂量和热稳定性等使其更适合光释光OSL-SAR方法测年。尽管现代样品的细颗粒比粗颗粒有更大的光释光（SAR-OSL）残余剂量，但阶地样品的细颗粒SAR-OSL年龄与地层层序的一致性表明细颗粒的光释光年代是可靠的。现代样品粗颗粒石英的光释光信号晒退较彻底，但阶地样品的粗颗粒石英SAR-OSL年龄与地层的不一致性和其较大的离散性，表明其SAR-OSL年龄的可靠性不如细颗粒石英。根据细粒石英的SAR-OSL年龄，研究阶地的形成年龄为64.7±2.5 ka。现代样品中的MET-pIRIR和回授光释光信号（TT-OSL）晒退不彻底，阶地沉积物样品钾长石的MET-pIRIR年龄远高于其对应的石英SAR-OSL年龄，并大于其上覆马兰黄土的年代上限。本研究说明在进行其他黄河阶地释光测年时，应同时应用粗粒和细粒石英，通过分析其光释光性质和样品的地貌沉积过程来确定其可靠性。在对阶地沉积物应用石英的TT-OSL和钾长石MET-pIRIR方法测年时需要特别谨慎。
关键词: 黄河/
基座阶地/
释光测年/
细粒与粗粒石英/
钾长石红外后多步高温红外法/
TT-OSL/
年龄可靠性

Abstract:The Yellow River flows along the northern and northeastern and borders of the Ordos Plateau, and cuts through the eastern plateau at an average elevation of 1050 m to 1500 m above sea level(a.s.l.) from north to south. Results in the formation of the Jinshaan Canyon limited to the reach from Lamawan to Yumenkou, and the canyon links the Weihe graben and the Hetao graben in the middle reach of the Yellow River. A series of strath terraces have been developed along the banks of the canyon, and the fluvial terrace deposits are covered by loess with various thicknesses. It is one of the key issues for its geomorphological studies to determine the accurate formation age of the terraces. Although there have been a lot of investigations about dating of the Yellow River terraces, especially for luminescence dating, the comparison of reliabilities of the ages obtained using different methods is rare. In this study, a typical strath terrace of the river in the Heiyukou area(38°32'36.34″N, 110°54'25.88″E) in the Jinshaan Canyon was identified at least five strath terraces on the two banks of the Yellow River. The second terraces was selected to be investigated in this study. The elevation of the river course in this area is about 770 m a.s.l., and the elevation of the strath surface is about 12.6 m above the modern channel. The terrace deposits which are 9.66 m in thick, are exposed in the river cliff and a sandpit, and can be divided into four layers. Five samples(samples HYK16-1~5) were collected from the fresh profile. About 12.6 m thick bedrock is exposed, which mainly comprises Triassic sandstone with a horizontal bedding. Note that the surface of the bedrock is loose because of weathering. A bedrock sample was also collected for testing its luminescence properties. In order to assess the bleaching of the fluvial deposits, a modern sample(HYK16-6) was taken from a sidebar at the foot of the river cliff. The modern sample is most likely deposited during the last flood. All six samples for luminescence dating using a single-aliquot regenerative-dose(OSL-SAR) protocol on fine-grained(FG) and coarse-grained(CG) quartz, and a multiple-elevated-temperature post-IR IRSL(MET-pIRIR) procedure on CG K-feldspar. A modern sample was also tested for its residual dose using two thermally transferred OSL(TT-OSL) procedure with different regenerative dose. The results show that the fine and coarse quartz grains have different luminescence properties due to their different sources, especially for some coarse quartz grains derived from the surface materials of local weathered sandstone bedrock. The fine quartz grains exhibit more fast component, higher saturation dose(>2000 Gy) and more thermal stability, which make them more suitable than the CG grains for luminescence dating. Although a large residual dose of the FG grains from the modern sample was detected, the FG quartz SAR-OSL ages are in stratigraphic order. This implies that the FG quartz SAR-OSL ages are more reliable. The CG quartz SAR-OSL ages are large scatter, and not stratigraphically consistent, suggesting that these ages are not reliable. Based on the FG SAR-OSL ages, the studied terrace was determined to 64.7±2.5 ka. The CG quartz thermally-transferred OSL(TT-OSL) and CG K-feldspar MET-pIRIR signals from the modern sample are very poorly bleached at deposition. The TT-OSL D_e value of up to 380 Gy for CG quartz is much larger than its corresponding SAR-OSL D_e value. The residual TT-OSL dose of the modern sample is related to the measured procedures and the size of the regenerate doses used. And the MET-pIRIR ages(106~148 ka) obtained for the terrace samples are much larger than their quartz SAR-OSL ages(50~70 ka) and beyond the upper age limit of the overlying Malan loess(71 ka). This study implies that when dating other Yellow River terraces both fine and coarse quartz fractions should be used in order to obtain reliable ages, and the reliability of FG and CG quartz OSL ages obtained must be evaluated on a case-by-case basis. Caution is needed when dating the Yellow River terraces with the MET-pIRIR and TT-OSL procedures.
Key words:Yellow River/
strath terraces/
OSL-SAR protocol/
fine-and coarse-grained quartz/
K-feldspar MET-pIRIR procedure/
TT-OSL/
reliability of ages



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