青海湖湖东地区近32 ka BP以来风沙沉积的粒度端元特征及环境意义

doi:10.19657/j.geoscience.1000-8527.2023.119

摘要/Abstract

摘要：

青海湖湖东地区出露典型的风成沉积,对气候变化响应敏感,为古气候环境的重建提供了良好研究窗口。本文选取湖东地区厚度10 m的风成砂-砂质古土壤剖面为对象,运用端元分析模型对沉积物粒度数据进行分析,提取对气候变化反映敏感的粒级组分,进一步结合粒度组分、磁化率指标,阐释各端元指示的环境意义以及近32 ka BP以来青海湖湖东地区的环境演化过程。结果表明,大水塘剖面粒度组成以砂粒物质为主,粉砂次之,黏粒最少。剖面的沉积物粒度组分可分解为3个端元:EM1是受冬季风影响的敏感粒径,指示冬季风的强弱变化;EM2指示的是区域环境受风沙作用的强弱,与EM1指示相反,但共同反映冬季风的强弱;EM3指示受区域性低空风系的影响,以尘暴的形式搬运沉积。青海湖湖东地区的环境演化过程可划分为4个阶段:(1)末次冰期间冰阶阶段(32~23.2 ka BP),气候整体较湿润,风沙活动较弱;(2)末次冰期冰盛期阶段(23.2~15.8 ka BP),气候冷偏干,风沙活动增强;(3)末次冰期冰消期阶段(15.8~9.5 ka BP),气候仍以冷偏干为主,冷暖波动,但存在小幅度升温;(4)全新世阶段(9.5 ka BP以来),早期转暖、中期最暖、晚期转凉,气候波动显著。

关键词: 端元分析, 风成砂, 环境演变, 青海湖

Abstract:

The typical aeolian sediments in the eastern part of Qinghai Lake are sensitive to climate changes, and these sediments provide an ideal window for the reconstruction of the paleoclimate environments.In this study, we selected an eolian sand-sandy paleosoil profile with a thickness of 10 m in the eastern area of Qinghai Lake as the study area.An end-member analysis model is used to analyze the data of sediment grain size, and the grain size components which are sensitive to climate changes are extracted thereafter.We combined the grain size and magnetic susceptibility indexes in our data analysis.We further discussed the environmental significance of each end-member indication and the environmental evolution in the eastern Qinghai Lake since 32 ka BP.The results show that the grain size component of the Dashuitang profile is mainly sand, and followed by silt, and the least is clay.The grain size components of sediments can be decomposed into three end-members: EM1, EM2, and EM3.EM1 is the sensitive grain size affected by winter monsoon, indicating the change of the strength of the winter monsoon.EM2 indicates the strength of regional environment affected by aeolian sand, which opposites to EM1.EM3 indicates sediment transport in the form of dust storms under the influence of a regional low-level wind system.The environmental evolution of the study area can be divided into four stages.During the last interglacial stage (32-23.2 ka BP), the climate was humid and the aeolian activities were relatively weak.During the last glacial maximum stage (23.2-15.8 ka BP), the climate was cold and dry, and the aeolian activities became stronger.During the last glacial deglaciation stage (15.8-9.5 ka BP), the climate was still mainly cold and dry, and the cold and warm fluctuated, but there is a small wave of warming.In the Holocene (since 9.5 ka BP), the climate fluctuated significantly.It was warm in the early period, warmest in the middle period, and cool in the late period.

Key words: end-member analysis, aeolian sand, environmental evolution, Qinghai Lake

中图分类号:

P532
P512.2

胡梦珺, 许澳康, 孙文丽, 庄静. 青海湖湖东地区近32 ka BP以来风沙沉积的粒度端元特征及环境意义[J]. 现代地质, 2024, 38(02): 487-496.

HU Mengjun, XU Aokang, SUN Wenli, ZHUANG Jing. Grain Size End-member Characteristics of the Aeolian Sediments in the East of Qinghai Lake and Its Environmental Significance Since 32 ka BP[J]. Geoscience, 2024, 38(02): 487-496.

图/表 9

图1 青海湖周边地区及剖面位置

Fig.1 Map of the area around Qinghai Lake and the profile position

图2 大水塘野外采样剖面(a)及年代-深度框架(b)(照片垂向高度对应于剖面深度刻度)

Fig.2 Field sampling profile (a) and age-depth frame (b) of Dashuitang

表1 大水塘剖面特征描述

Table 1 Characterization of the Dashuitang profile

层序	地层名称	深度(m)	特征描述
1	表土层	0~0.3	灰黄色,松散,见植物根系
2	风砂层	0.3~ 1.3	灰黄白色中细砂,见少量植物根系
3	砂质古土壤层	1.3~2.3	深灰色,细砂,较紧实,有假菌丝体
4	风砂层	2.3~ 3.8	浅灰色,中细砂,存在风成加积纹层
5	砂质古土壤层	3.8~ 5.0	深灰色,细砂,较紧实
6	风砂层	5.0~5.3	灰白色,细砂,松散
7	砂质古土壤层	5.3~6.6	暗棕色粉砂,紧实,见白菌丝体
8	风砂层	6.6~7.7	粉砂和黏粒为主
9	砂质古土壤层	7.7~10.0	黏粒为主,胶结紧实

表2 大水塘剖面的光释光测年数据

Table 2 Results of OSL dating from the Dashuitang profile

样品编号	采样深度(m)	测试指标						年龄±误差 (ka BP)
样品编号	采样深度(m)	U(10^-6)	Th(10^-6)	K(10^-6)	等效剂量(Gy)	年剂量(Gy/ka)	含水量(%)	年龄±误差 (ka BP)
08G-356	1.66~1.70	1.31	6.04	1.40	3.21±0.30	2.63	3.2	1.2±0.1
08G-357	2.56~2.60	0.84	4.80	1.35	5.20±0.08	2.29	2.5	2.3±0.1
08G-358	3.66~3.70	1.24	5.48	1.41	6.95±0.64	2.50	4.6	2.8±0.2
08G-359	5.26~5.30	1.36	6.45	1.38	8.82±0.29	2.60	3.6	3.4±0.1
08G-360	5.30~5.34	1.30	6.66	1.46	12.30±0.28	2.68	4.1	4.6±0.1
10G-46	5.92~5.96	1.43	7.47	1.57	25.75±1.48	2.94	5.0	8.7±0.6
10G-45	6.20~6.24	1.28	5.76	1.64	26.35±0.72	2.75	7.3	9.5±0.5
08G-362	6.60~6.64	1.50	7.35	1.45	42.54±1.95	2.71	9.3	15.8±0.7
08G-364	7.62~7.66	1.81	7.55	1.53	68.65±2.17	2.97	0.8	23.2±1.1
08G-365	9.96~10.0	1.45	6.73	1.51	86.45±2.97	2.91	6.0	31.9±1.3

图3 大水塘剖面沉积物不同粒级及粒度敏感指标的垂直变化

Fig.3 Vertical variations of the different grain sizes and sensitive indexes of the Dashuitang profile

图4 大水塘剖面的端元分析结果 (a)决定系数R2;(b)角偏度差;(c)端元粒度频率分布曲线

Fig.4 End-member analysis results of the Dashuitang profile

图5 大水塘剖面各端元、磁化率和平均粒径在深度上的变化

Fig.5 Variations of each end-member, magnetic susceptibility and average grain size with the depth of the Dashuitang profile

表3 大水塘剖面各端元和平均粒径的相关分析

Table 3 Correlation analysis between the end-members and average grain size of the Dashuitang profile

相关分析	EM1	EM2	EM3	平均粒径
EM1	1
EM2	-0.912^*	1
EM3	-0.021	0.209	1
平均粒径	-0.903^*	0.698^*	0.328^*	1

图6 大水塘剖面端元与其他古环境记录对比 (a)EM1;(b)EM2;(c)青海湖大水塘剖面沉积物平均粒径[10];(d)西宁木里剖面沉积物平均粒径[42];(e)青海湖QH1孔沉积物总有机碳[53];(f)洛川剖面有机碳同位素δ13C组成[48];(g)格陵兰冰心氧同位素δ18O组成[51]

Fig.6 Comparison of the end-members of the Dashuitang profile with other paleoenvironmental records

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