皋兰山红黏土-黄土记录的上新世-更新世转型期C_(3)/C_(4)植被演化  

The C_(3)/C_(4) vegetation history during the Pliocene-Pleistocene transition:evidence from the Gaolanshan red clay-loess deposition

作　　者：李孟 彭廷江 韩冰雁 郭本泓 李小苗[1] 马振华[1] 冯展涛 宋春晖 LI Meng;PENG Tingjiang;HAN Bingyan;GUO Benhong;LI Xiaomiao;MA Zhenhua;FENG Zhantao;SONG Chunhui(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou 730000,China;School of Earth Science,Lanzhou University,Lanzhou 730000,China)

机构地区：[1]兰州大学资源环境学院西部环境教育部重点实验室,甘肃兰州730000 [2]兰州大学地质科学与矿产资源学院,甘肃兰州730000

出　　处：《冰川冻土》2021年第3期798-808,共11页Journal of Glaciology and Geocryology

基　　金：国家自然科学基金项目(41971099;41330745;42001074;41401214)资助。

摘　　要：上新世-更新世转型是上新世温暖气候向更新世冰期-间冰期旋回过渡的重要时段,与此同时,青藏高原的强烈隆升也深刻改变了高原及周边地区的地貌格局和生态环境面貌。因此,开展青藏高原东北缘地区上新世-更新世转型期的古气候变化研究是理解地球各圈层相互作用的重要切入点。而兰州盆地地处中国三大自然区的衔接位置,对气候变化和构造活动响应较为敏感,是探讨构造-气候-生态相互作用的理想区域。以兰州皋兰山红黏土-黄土岩芯为研究对象,在已有黄土高精度磁性地层年代学基础上,综合开展了有机碳同位素和长链正构烷烃碳同位素分析,重建了西部黄土高原上新世-更新世转型期(3.0~2.2 Ma)的C_(3)/C_(4)植被相对丰度演化历史。结果表明:皋兰山上新世-更新世转型期风成沉积中正构烷烃多以C31为主峰的单峰模式,可能指示了草本植被的主要贡献。而典型黄土层位(L32和L33)的正构烷烃多呈现微生物降解的双鼓包模式,表明饱和烃受外源输入影响。综合对比常规指标、总有机碳和长链正构烷烃碳同位素后认为,皋兰山底部黄土的总有机碳同位素不能直接用于重建区域C_(3)/C_(4)植被演化。长链正构烷烃碳同位素研究表明:在3.0~2.2 Ma时期,皋兰山古生态整体以C3植被为主;C4植被扩张发生在3.0 Ma之前,3.0~2.9 Ma发生C4植被快速减少事件,初步推测这可能与降温有关。As the critical stage from the Pliocene to the Quaternary,the Pliocene-Pleistocene transition during the interval of 3.0~2.2 Ma obviously experienced climate change from warm climate to the Pleistocene glacialinterglacial cycles.Meanwhile,the Tibetan Plateau also experienced intensive tectonic uplift,the ecological en⁃vironment and geomorphologic pattern of the Tibetan Plateau and its surrounding areas have been significantly shaped.So the detailed research on the paleoenvironment evolution during the Pliocene-Pleistocene transition can shed new lights on the coupled relationships among the atmosphere,biosphere and lithosphere.The Lan⁃zhou Basin is the ideal place to discuss the interactions between the tectonic uplift,global cooling and regional ecosystem.Here the Gaolanshan red clay-loess sequence from the Lanzhou Basin were detailed analyzed via the n-alkanes distribution and organic geochemistry(total organic carbon and long-chain n-alkanes carbon isotopes)methods.Particularly,the C_(3)/C_(4)relative abundance evolution history during the interval of 3.0~2.2 Ma in Lan⁃zhou Basin were reconstructed.In detail,the n-alkanes of Gaolanshan red clay-loess sequence during the inter⁃val of 3.0~2.2 Ma mainly be characterized with unimodal pattern and the C31 main peak,which implicates the contribution of grassland vegetation.In addition,the n-alkanes distribution of typical loess L32 and L33 show the existence of double bulge,obviously implicating the microbial activities.After the integration of total organ⁃ic carbon isotope,long-chain n-alkanes carbon isotope and grain sizes,we proposed that organic carbon isotope could be affected by exogenous input via the mixing n-alkanes by the wind.Therefore,we suggested that the to⁃tal organic carbon isotopes should not be used to reconstruct the C_(3)/C_(4)relative abundance during the Pliocene-Pleistocene transition in the Lanzhou Basin.Based on the integrated evidence of classical proxies and leaf wax compound-specific carbon isotope,the Gaolanshan paleoecology

关 键 词：兰州皋兰山 上新世-更新世转型 总有机碳同位素 单体碳同位素 C_(3)/C_(4)植被演化 

分 类 号：Q941[生物学—植物学]