| 引用本文: | 方亚会，方小敏，昝金波，张涛，杨一博，叶程程，白艳.2019.西宁盆地总有机碳同位素记录的~39 Ma亚洲内陆急剧干旱事件[J].地球环境学报,10(5):453-464 |
| FANG Yahui, FANG Xiaomin, ZAN Jinbo, ZHANG Tao, YANG Yibo, YE Chengcheng, BAI Yan.2019.An Asian inland aridification enhancement event at ~39 Ma recorded by total organic carbon isotopes from Xining Basin[J].Journal of Earth Environment,10(5):453-464 |
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| 摘要: |
| 始新世亚洲内陆干旱环境演化（简称干旱化）的研究比较匮乏，驱动机制存在争议。位于青藏高原东北缘的西宁盆地含有连续的始新世地层沉积序列，是研究上述科学问题的理想材料。通过西宁盆地中央西宁东和水湾平行剖面（古地磁年代均为~43 Ma—~35 Ma）详细的总有机碳同位素记录，对始新世的干旱生态环境变化进行了研究，结果显示：上述两个平行剖面总有机碳同位素平均值均在~39 Ma发生了急剧的~2.5‰变正（分别从−27.5‰和−28.4‰变正为−25.0‰和−26.0‰），结合盆地内耐旱植物麻黄属和白刺属孢粉的百分含量急剧升高，共同指示该时期的西宁盆地发生了急剧干旱化。副特提斯海退却导致的水汽输送的减少可能是驱动西宁盆地始新世干旱生态环境变化的主要原因，全球长期变冷可能起到了背景叠加作用。 |
| 关键词: 西宁盆地 ~39 Ma 总有机碳同位素 亚洲内陆干旱化 副特提斯海退却 |
| DOI：10.7515/JEE192009 |
| CSTR：32259.14.JEE192009 |
| 分类号: |
| 基金项目:中国科学院战略性先导科技专项（XDA20070201） |
| 英文基金项目:Strategic Priority Research Program of Chinese Academy of Sciences (XDA20070201) |
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| An Asian inland aridification enhancement event at ~39 Ma recorded by total organic carbon isotopes from Xining Basin |
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FANG Yahui, FANG Xiaomin, ZAN Jinbo, ZHANG Tao, YANG Yibo, YE Chengcheng, BAI Yan
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1. CAS Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China
2. University of Chinese Academy of Sciences, Beijing 10049, China
3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences (CAS), Beijing 100101, China
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| Abstract: |
| Background, aim, and scope The Cenozoic evolution of the aridification of the Asian interior has attracted major research interest in recent years. However, the history of aridification during the Eocene has been neglected and the forcing mechanism remains controversial. Xining Basin, located on the northeastern margin of the Tibetan Plateau, contains a thick sequence of Cenozoic fine grained sedimentary sequences which have been dated using high-resolution paleomagnetic studies. Thus, Xining Basin is well suited for studying the history of regional aridification and its forcing mechanisms. In this study, we selected two parallel early Cenozoic sections in the Xining Basin spanning the interval from ~43 Ma to ~35 Ma, for analysis of the stable isotope composition of total organic carbon (δ13CTOC ). Our aim was to reconstruct the history of aridification during the Eocene. Materials and methods The mudstone was sampled at intervals of 1—2 m with 96 samples being obtained from the East Xining Section, and 94 samples from the Shuiwan Section. The samples were pretreated with 2 mol·L−1 HCl to remove carbonate and the stable carbon isotope composition of the treated samples was measured on a Thermo Delta V mass spectrometer interfaced with a Flash EA 1112 elemental analyzer. Results The δ13CTOC records of the two parallel sections in Xining Basin both exhibit an abrupt ~2.5‰ increase at ~39 Ma. Discussion The distribution of n-alkanes and the δ13CTOC values indicate the organic matter is mainly derived from terrestrial C3 plants; provenance of the sediments remained constant. Thus, the increase of δ13C TOC at ~39 Ma in Xining Basin can be mainly attributed to environmental factors that have influenced the carbon isotopic composition of terrestrial C3 plants. The concentration and carbon isotopic values of atmospheric CO2 can be excluded from the list of potential causal factors. Precipitation and temperature both have a negative relationship with the carbon isotopic composition of terrestrial C3 plants, the effect of the former is stronger. Notably, there was no abrupt decrease in global temperature at ~39 Ma and therefore, a decrease in precipitation was the principal cause of the carbon isotopic shift at ~39 Ma in the Xining Basin. An aridification enhancement event at ~39 Ma is also recorded by other proxies, such as pollen and spore assemblages, from other sections in Xining Basin as well as Qaidam Basin. It is likely that the retreat of Paratethys Sea was the main factor responsible for the reduction in precipitation in Xining Basin, against the background of global cooling. Conclusions The stable carbon isotope records of the total organic fraction of the sediments of Xining Basin reveals an abrupt enhancement of aridification happened at ~39 Ma, which is confirmed by other proxy records from the region. The retreat of Paratethys Sea was likely the principle cause, while global cooling played a less important role. Recommendations and perspectives The explanation for Asian inland aridification at ~39 Ma still remains controversial and further research is needed to determine the cause. |
| Key words: Xining Basin ~39 Ma total organic carbon isotope Asian inland aridification retreat of Paratethys Sea |
