| 引用本文: | 杨茂洁,常宏,罗家馨,李乐意,贺茂勇,易庭楠.2026.晚中新世-早更新世时期罗布泊水体氧化-还原条件变化对干旱化过程的响应[J].地球环境学报,17(4):894-908 |
| YANG Maojie,CHANG Hong,LUO Jiaxin,LI Leyi,HE Maoyong,YI Tingnan.2026.Response of changes in redox conditions in the Lop Nur lakes to the process of aridification during the Late Miocene-Early Pleistocene[J].Journal of Earth Environment,17(4):894-908 |
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| 摘要: |
| 亚洲内陆干旱区的形成演化与青藏高原隆起和全球变化等密切相关，塔里木盆地作为北半球中纬度干旱地区的典型代表，其干旱化过程及动力学机制对区域生态重建及未来区域预测具有重要的意义。盆地内多个剖面及钻孔岩芯研究显示，新近纪以来区域干旱化始于晚中新世，而这一过程的驱动机制仍存在争议。塔里木盆地东部罗布泊湖泊水体深度的演化可有效地重建区域水文变化历史，从而阐明干旱化的根本原因。文章采用矿物自动定量分析系统（AMICS）对晚中新世-早更新世（6.86—2.00 Ma）罗布泊湖相沉积（深度为1003.92—123.83 m）的生物成因矿物进行分析，试图重建湖泊沉积环境的氧化还原条件及水位波动演变历史。矿物分析结果表明，生物成因矿物包括白云石（0—8.46%）、含镁方解石（0—0.59%）、菱铁矿（0—0.44%）以及黄铁矿（0—6.97%）。白云石、菱铁矿和黄铁矿主要形成于低氧或还原性的沉积环境（相对较深的湖泊），而含镁方解石则在相对富氧的沉积条件下形成（浅湖）。生物成因矿物组合变化过程揭示，罗布泊在6.86—2.0 Ma经历了三次湖退期（气候干旱）和两次湖进期（气候湿润）的交替，三次湖退期分别发生在6.86—6.38 Ma、5.60—3.60 Ma以及2.70—2.0 Ma，而两次湖进期分别发生在6.38—5.60 Ma和3.60—2.70 Ma。第二次湖退期（5.60—3.60 Ma）是湖泊沉积环境发生根本性改变的重要时期，其在4.92 Ma（673.52 m以上深度）向氧化性更强的条件转变，标志着湖泊进入了长期的低水位状态。生物成因矿物组合记录了晚中新世以来塔里木盆地罗布泊古湖泊演化，该过程与西风带演变有关。区域对比及多参数分析指出，全球变冷驱动西风强度和路径的改变可能是塔里木气候干旱化的主要原因，特提斯西退和青藏高原生长均可能加剧了该过程。 |
| 关键词: 生物成因矿物 氧化还原条件 塔里木盆地 西风带 全球变冷 亚洲内陆干旱化 |
| DOI：10.7515/JEE2024190 |
| CSTR：32259.14.JEE2024190 |
| 分类号: |
| 基金项目:国家自然科学基金项目（42372221）；中国科学院战略性先导科技专项（B类）（XDB40010103） |
| 英文基金项目: |
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| Response of changes in redox conditions in the Lop Nur lakes to the process of aridification during the Late Miocene-Early Pleistocene |
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YANG Maojie1，2，CHANG Hong1，LUO Jiaxin1，2，LI Leyi1，HE Maoyong1，YI Tingnan1，2
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1.State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061 , China 2.University of Chinese Academy of Sciences, Beijing, 100049 , China
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| Abstract: |
| Background, aim, and scope Formation and evolution of Asian inland arid regions are intricately tied to the uplift of the Qinghai-Xizang Plateau and global changes. As a typical representative of the arid region in the mid-latitude of the Northern Hemisphere, the drought process and its dynamics in the Tarim Basin are of great significance for regional ecological reconstruction and future climate prediction. Studies from numerous profiles and drill cores within the basin indicate that aridification intensified in the Late Miocene, whereas the driving mechanisms triggering this process remain contentious. The evolution of water depth of the Lop Nur in the eastern Tarim Basin can offer a reliable method to infer the hydrological cycle in the basin, thereby elucidating the causes of increased desertification. This paper is dedicated to reconstruct the evolution of redox conditions and then water-level fluctuation within the Lop Nur by analyzing the biogenic mineral content for drill core Ls2 in the eastern Tarim Basin spanning the Late Miocene-Early Pleistocene (6.86—2.00 Ma), aiming to infer the evolution of water depth. Materials and methods Mineralogical analyses were carried out for samples from drill core Ls2 (39°46′39.3′′N，88°23′18.2′′E), covering a depth range of 1003.92—123.83 m which was assigned to 6.86—2.00 Ma on the basis of the magnetostratigraphy. A total of 183 samples were collected at ca. 5 m intervals for mineral analysis employing the Advanced Mineral Identification and Characterization System (AMICS). AMICS is an automated mineral identification and analysis system that utilizes scanning electron microscopy (SEM) technology. It integrates a Bruker energy-dispersive X-ray spectrometer (EDX, model XFlash 7) and a ZEISS scanning electron microscope (SEM, model EVO-18), controlled by dedicated AMICS. The system employs the high-sensitivity backscattered electron (BSE) imaging capabilities of SEM to achieve high-resolution mineralogical imaging. Biogenic mineral grains can be segmented with sub-grain-level precision. Combined with its integrated analytical database by AMICS’s image analysis functions, AMICS enables quickly and accurately identification of biogenic minerals. Simultaneously, SEM is used to observe biogenic mineral morphology, capturing distinct morphological characteristics of different minerals with high resolution. Results Mineral data show that biogenic minerals are composed principally of dolomite（0—8.46%）, magnesian calcite（0—0.59%）, siderite (0—0.44%), and pyrite (0—6.97%). Discussion Dolomite, siderite, and pyrite predominantly form in low-oxygen or reducing environments (relatively deep-lake settings), whereas magnesian calcite is indicative of relatively oxidizing conditions (typical of shallow-lake environments). The variations in biogenic mineral assemblages demonstrate that Lop Nur has undergone three periods of lake shrinkage (characterized by reduced dolomite and siderite and/or increased magnesian calcite, with the occurrence or complete absence of large-grained strawberry pyrite) and two periods of lake expansion (marked by increased dolomite, siderite, and fine-grained strawberry pyrite or decreased magnesian calcite in sediments) during 6.86—2.00 Ma. Specifically, the lake shrinkage (dry climate) occurred at 6.86—6.38 Ma, 5.60—3.60 Ma, and 2.70—2.00 Ma, while the lake expansion (wet climate) were at 6.38—5.60 Ma and 3.60—2.70 Ma. The second retraction phase (5.60—3.60 Ma) represents a critical phase of fundamental shift in the lake’s sedimentary environment, which transitioned from reducing to more oxidizing conditions at 4.92 Ma (core section above 673.52 m), marking the onset of a long-term low water level state in the Lop Nur. The hydrological evolution of the Lop Nur paleolake suggests that aridification in Asian inland basins has intensified in tandem with global ice volume expansion since the Late Miocene. The increasing of Northern Hemisphere ice volume reduced global marine evaporation, thereby decreasing the moisture supply to inland basins. Comparison with contemporaneous climate records from adjacent regions reveals that the uplift of the Tibetan Plateau exacerbated regional aridity disparities through modulating moisture redistribution, the primary driver of regional aridification was the southward shift of westerlies induced by global cooling since Late Miocene. Furthermore, the regression of Tethys Sea likely amplified water scarcity in Asian inland basins by altering Atlantic moisture transport pathways. Conclusions The biogenic mineral assemblages provide records of lacustrine environmental shifts with high-precision, revealing that although the Tethys Sea regression and the Qinghai-Xizang Plateau uplift may have contributed to accelerating Asian interior aridification, the intensity and pathway changes of westerlies driven by global cooling were the primary factor on the aridification during the Late Miocene-Early Pleistocene (6.86—2.00 Ma). Recommendations and perspectives To better elucidate the driving mechanisms of aridification in inland Asia since Neogene, future research will prioritize improving the comparative analysis between multi-scale climate models and biogenic mineral records, to advance the understanding of the effects of westerlies migration on the hydrological cycle in inland Asia. |
| Key words: biogenic minerals redox conditions Tarim Basin westerlies global cooling aridification in Asian inland |
