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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Miocene sedimentary environment and climate change in the northwestern Qaidam basin, northeastern Tibetan Plateau: Facies, biomarker and stable isotopic evidences
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Miocene sedimentary environment and climate change in the northwestern Qaidam basin, northeastern Tibetan Plateau: Facies, biomarker and stable isotopic evidences

机译：青藏高原东北部柴达木盆地西北部的中新世沉积环境和气候变化：相，生物标志物和稳定的同位素证据

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摘要

Facies, biomarker and stable isotopic records fromtheMiocene lacustrine sediments in the northwestern Qaidam basinwere investigated to reconstruct theMiocene sedimentary environment and climatic history. Three distinct facies can be recognized. These include the following: (1) gray–black laminated mudstone andmarlstone, which represent a semi-deep fresh to semi-brackish lake environment; (2) gray, yellowish massive mudstone, marlstone and siltstone; and (3) yellowishmassive sandstone,which imply a shallowbrackish lake environment. The decreasing C_(27)/C_(31) and (C_(27)+C_(29))/(C_(31)+C_(33)) values, the increasing ACL (mean chain length) values of nalkanes and the vertical evolution of sedimentary environments indicate the overall intensified aridity, which is considered to be an integrated result of high elevation of the Himalaya–Tibetan system, retreat of the Paratethys and global cooling. High fluctuations of the δ~(18)O values and primary dolomite contents reveal the hydrologically closed paleolake with intermittently open conditions in the study area duringmiddle–late Miocene. The Qaidam basin is suggested to be hydrologically segmented, based on the stable isotopic data comparison between the study area and the northeastern area. The most negative end of the oscillations of the δ~(18)O values (indicating the minimal evaporation), which likely represents the isotopic ratio of the meteoric water, surprisingly conveys stability in the Shang Youshashan and Shizigou Formations and displays a positive ~2.5‰ shift. This significant shift was probably due to the climatic aridification and air mass changes around 10–8 Ma rather than the global cooling.
机译：研究了柴达木盆地西北部中新世湖相沉积相的相，生物标志物和稳定的同位素记录，以重建中新世的沉积环境和气候历史。可以识别三个不同的相。其中包括：（1）灰黑色夹层泥岩和玛石岩，代表半深的新鲜至半咸水湖泊环境; （2）灰色，淡黄色块状泥岩，马林岩和粉砂岩; （3）淡黄色块状砂岩，暗淡浅湖环境。递减的C_（27）/ C_（31）和（C_（27）+ C_（29））/（C_（31）+ C_（33））值，醛烷的ACL（平均链长）值增加以及沉积环境的垂直演变表明总体上干旱加剧，这被认为是喜马拉雅－西藏系统高海拔，Paratethys撤退和全球降温的综合结果。 δ〜（18）O值和主要白云岩含量的高波动揭示了中新世中晚期研究区的水文封闭古陆与间歇性开放条件。根据研究区域和东北地区之间稳定的同位素数据比较，建议对柴达木盆地进行水文分割。 δ〜（18）O值的振荡的最负端（指示最小蒸发），可能代表着流水的同位素比，出乎意料地传达了上幽沙山和石子沟组的稳定性，并显示出正值〜2.5 ‰移位。这种重大变化可能是由于气候干旱和大约10-8 Ma的空气质量变化，而不是全球变冷所致。

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