柴达木盆地中新世-早上新世有机碳同位素记录和植被演化历史  

ORGANIC CARBON ISOTOPIC RECORD AND VEGETATION EVOLUTION HISTORY IN THE QAIDAM BASIN DURING MIOCENE-EARLY PLIOCENE

作　　者：苏庆达 聂军胜[2] 李祥忠 高鹏 SU Qingda;NIE Junsheng;LI Xiangzhong;GAO Peng(Shandong Provincial Key Laboratory of Water and Soil Conservation and Environmental Protection,College of Resources and Environment,Linyi University,Linyi 276000,Shandong;Key Laboratory of Western China'Environmental Systems,Ministry of Education,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou 730000,Gansu;Yunnan Key Laboratory of Earth System Science,Yunnan University,Kunming 650500,Yunnan)

机构地区：[1]临沂大学资源环境学院,山东省水土保持与环境保育重点实验室,山东临沂276000 [2]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 [3]云南大学云南省地球系统科学重点实验室,云南昆明650500

出　　处：《第四纪研究》2022年第4期948-957,共10页Quaternary Sciences

基　　金：科技部第二次青藏高原综合科学考察研究项目“碰撞以来古地理格局与构造地貌过程”(批准号:2019QZKK0704)资助。

摘　　要：晚中新世C_(4)植被扩张的过程和驱动机制是全球古气候变化研究的焦点问题。然而,这一生态格局的转变在亚洲中纬度地区的扩张范围尚存在争议,阻碍了对中国北方陆地生态系统的形成及其与高原隆起关系的清晰认识。青藏高原东北缘柴达木盆地河湖相沉积保存了晚新生代连续的古生态演化记录,是研究这一科学问题的理想载体。本研究选取柴达木盆地已具有古地磁年代的、厚度约6200 m的大红沟剖面河湖相地层,通过有机碳同位素和正构烷烃分析,恢复了高原东北缘约20.5~4.4 Ma的植被演变历史。结果发现,大红沟剖面典型样品正构烷烃C_(27)、C_(29)和C_(31)组分含量占总含量的绝大多数,且具有明显的奇偶优势,指示陆生高等植物是该剖面河湖相沉积物有机质的主要来源;大红沟剖面有机碳同位素记录指示中新世-早上新世青藏高原东北缘生态系统以C_(4)植物为主且晚中新世没有出现C_(4)植被的大规模扩张,这与低海拔的中国北方晚中新世C_(4)植被大规模扩张的观点不同。晚中新世较低的大气CO_(2)浓度和高原隆升引发亚洲夏季风降水增强有利于晚中新世C_(4)植被的扩张,而晚中新世C_(4)植被的大规模扩张并没有发生于青藏高原东北缘。据此推测这可能是晚中新世高原东北缘构造抬升造成植物生长季温度较低,限制了C_(4)植物的生长。这一研究为晚中新世高原东北缘构造隆升提供了间接的生态学证据。The processes and driving mechanisms of the Late Miocene C_(4) plants expansion is a key issue of global paleoclimatic change.Paleoecological records from low and middle latitudes demonstrate a global expansion of C_(4) plants during the Late Miocene.However,significant debate exists about the spatial extent of this profound ecological change in mid-latitude Aisa,hindering a clear understanding of the formation of terrestrial ecosystems in mid-latitude Northern China and its relationship with plateau uplift.Here we present n-alkanes and carbon isotopic records from a 6200 m-thick Miocene-Early Pliocene Dahonggou stratigraphic section in the northern Qaidam Basin to infer the paleovegetation changes and understand the interplay between the construction of terrestrial ecosystems and Tibetan Plateau uplift.The Qaidam Basin is surrounded by the Altyn Shan to the northwest,the Qilian Shan to the northeast,and the Kunlun Shan to the south,and sits at an average elevation of ca.3000 m above sea level.The internally drained Qaidam Basin covers an area of ca.12.1×10^(4)km^(2) and is a key region to test models about various uplift mechanisms of the Tibetan Plateau.The studied Dahonggou section(37°32'55″N,95°09'56″E to 37°28'42″N,95°07'57″E)lies on the southern limb of the Xitieshan Anticline in the northern Qaidam Basin.The studied Dahongou section is divided into six formations:Lulehe Formation,Xiaganchaigou Formation,Shangganchaigou Formation,Xiayoushashan Formation,Shangyoushashan Formation,and Shizigou Formation.Past studies have attributed the Lulehe Formation to a Paleocene-Eocene age based mainly on pollen and ostracoda fossils.Paleomagnetic dating and Neogene mammal fossils(the“Honggou fauna”),constrain the age to Early Miocene-Pliocene(from ca.20.5 Ma to ca.4.4 Ma).The discussion of Dahonggou paleovegetation evolution is based on the new chronological model(ca.20.5 Ma to 4.4 Ma)in this study.For organic carbon isotopic analysis,a total of 39 fluvio-lacustrine samples were measured in ca.200~300 m

关 键 词：柴达木盆地 晚中新世 有机碳同位素和正构烷烃 C_3/C_4植被 

分 类 号：P597.2[天文地球—地球化学] P593[天文地球—地质学] P534.621