曾方明^1,2,3,,
杨欢³,
卞昊昆⁴
1. 中国科学院青海盐湖研究所, 中国科学院盐湖资源综合高效利用重点实验室, 青海 西宁 810008
2. 中国科学院青海盐湖研究所, 青海省盐湖地质与环境重点实验室, 青海 西宁 810008
3. 中国地质大学(武汉), 生物地质与环境地质国家重点实验室, 湖北 武汉 430074
4. 北京化工大学生命科学与技术学院, 北京 100029

基金项目: 国家自然科学基金项目（批准号：41402314）、中国地质大学（武汉）生物地质与环境地质国家重点实验室开放基金项目（批准号：GBL21307）和中国科学院青年创新促进会专项项目（批准号：2017468）共同资助


详细信息

作者简介: 曾方明, 男, 36岁, 副研究员, 第四纪地质学专业, E-mail:fmzeng@163.com

中图分类号: P534.63⁺2;P593

收稿日期:2018-03-24
修回日期:2018-06-18
刊出日期:2018-09-30

GDGTs compounds of the Holocene eolian deposits in Qinghai Lake area and their paleoenvironmental implications

Zeng Fangming^1,2,3,,
Yang Huan³,
Bian Haokun⁴
1. Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, Qinghai
2. Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, Qinghai
3. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences(Wuhan), Wuhan 430074, Hubei
4. College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029


MSC: P534.63⁺2;P593

--> Received Date: 24 March 2018
Revised Date: 18 June 2018
Publish Date: 30 September 2018


摘要
摘要:青海湖晚第四纪的古环境演化和湖面变化是学术界长期关注的热点问题，争议也较多。我们对青海湖地区种羊场（ZYC）剖面（120 cm厚）全新世风尘堆积的GDGTs（甘油二烷基甘油四醚）化合物相关指标的古环境意义进行了初步研究，以期从一个新的角度对上述问题进行探讨。研究结果表明：1）ZYC剖面的TEX₈₆（由86个碳原子组成的四醚指标）与磁化率正相关，而R_i/b比值（类异戊二烯GDGTs与支链GDGTs丰度的比值）与磁化率负相关。2）ZYC剖面的TEX₈₆指标与湖泊岩芯胖真星介（Eucypris inflata）壳体δ¹⁸O指示的7月古水温及长链烯酮（U₃₇^K）指示的夏季古水温变化具有相似的变化特征，显示TEX₈₆指标较可靠地指示了青海湖地区的大气温度变化。然而，ZYC剖面的MBT（甲基化指数）和CBT（环化指数）指标在重建古气温方面具有一定的局限性，可能与青海湖地区全新世出现的干旱环境有关。3）ZYC剖面的R_i/b比值与湖泊岩芯E.inflata壳体Sr/Ca比值指示的青海湖湖水的古盐度具有较一致的变化特征，表明R_i/b比值较有效地指示了青海湖地区环境的干湿状况。4）TEX₈₆和R_i/b指标揭示青海湖区在9.5~7.5 ka B.P.为冷干时期；7.5~5.5 ka B.P.为独特的温干阶段，温度在6.2 ka B.P.左右达到最高值；5.5~1.7 ka B.P.为温湿时期；1.7~0 ka B.P.为冷干时期。5）风尘堆积的GDGTs记录表明：7.5~5.5 ka B.P.由于环境干旱，青海湖不太可能出现高湖面；5.5~1.7 ka B.P.由于环境湿润，青海湖很可能出现全新世高湖面；1.7 ka B.P.以来，青海湖地区的气候快速变干。
关键词: 青海湖/
风尘堆积/
环境变化/
GDGTs (glycerol dialkyl glycerol tetraethers, 甘油二烷基甘油四醚)

Abstract:Qinghai Lake area, located in the northeastern Qinghai-Tibetan Plateau(NE QTP), is affected by the East Asian monsoon, South Asian monsoon and the Westerlies. Thus, it is a sensitive region for studying the paleoenvironmental changes since the Late Quaternary on the NE QTP. In the past, a large number of researches have been made by investigating the lacustrine sediments drilling from the Qinghai Lake, shorelines around the lake, and eolian deposits around the lake. All these studies aimed to reconstruct the details of environmental evolution since the Late Quaternary and their controlling factors. However, there are still controversies among different studies. For example, there are different viewpoints about the periods of the high lake level of Qinghai Lake. Here we present GDGTs(glycerol dialkyl glycerol tetraethers) of the eolian deposits from the ZYC(Zhongyangchang site) section in the eastern shore of the Qinghai Lake. The GPS position of the ZYC section is 36.63°N, 100.87°E. The thickness of this section is 120 cm. ZYC section is well dated by OSL(optically stimulated luminescence) method. OSL ages show that the age at the depth of 100 cm is about 9.5 ka B.P. Twenty-five samples at 4-cm intervals from the 0~100 cm depth of the ZYC section are chosen to do GDGT analysis. TEX₈₆ index(TetraEthers indeX of tetraethers consisting of 86 carbon atoms), MBT(the methylation index of branched tetraethers), CBT(the cyclisation ratio of branched tetraethers), and R_i/b[the abundance ratio of archaeal isoprenoid GDGTs(isoGDGTs) to bacterial branched GDGTs(brGDGTs)]are calculated based on the abundances of GDGTs. The results show that:(1) GDGTs in eolian deposits from the ZYC section are composed of isoGDGTs and brGDGTs, and the concentration of GDGTs is positively correlated with TOC(total organic carbon) content. In general, magnetic susceptibility is indicative of precipitation and air temperature recorded in eolian deposits on the Chinese Loess Plateau and NE QTP. In the ZYC section, TEX₈₆ is positively correlated with magnetic susceptibility, while R_i/b is negatively correlated with magnetic susceptibility. (2) TEX₈₆ time series in the ZYC section is consistent with reconstructed July water temperature changes by δ¹⁸O in the shell of ostracod(Eucypris inflata) and summer water temperature changes by long chain alkenones(U₃₇^K), suggesting that TEX₈₆ index can be treated as a proxy to reconstruct atmosphere temperature during the Holocene in Qinghai Lake area. However, MBT-CBT index is not a good paleothermometer in the ZYC section. It is probably affected by arid environment occurred during the Holocene in Qinghai Lake area. (3) R_i/b ratio in eolian deposits of the ZYC section can be well compared with Sr/Ca ratio in shell of E.inflata from drill core QH-16A in Qinghai Lake, especially during 7.0~1.7 ka B.P. The Sr/Ca ratio is demonstrated to indicate salinity change of the water in Qinghai Lake since Holocene. Salinity of Qinghai Lake is affected by environmental condition in Qinghai Lake area. Thus, R_i/b ratio index would be treated as a proxy to reconstruct humidity information recorded in eolian deposits of the ZYC section. (4) TEX₈₆ and R_i/b indicate that 7.5~5.5 ka B.P. is warm-dry period, other periods of Holocene are dominated by warm-humid(5.5~1.7 ka B.P.) or cold-dry(9.5~7.5 ka B.P. and 1.7~0 ka B.P.) periods. The air temperature was the highest at ca. 6.2 ka B.P. (5) For the environment was arid during 7.5~5.5 ka B.P. in Qinghai Lake area, the high lake level of Qinghai Lake should not occur. Environment was humid during 5.5~1.7 ka B.P., so the high lake level of Qinghai Lake would appear. 1.7~0 ka B.P., results of GDGT proxies show that the environment was arid.
Key words:Qinghai Lake/
eolian deposit/
environmental change/
GDGTs (glycerol dialkyl glycerol tetraethers)



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