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XUE Liyuan,DING Xuan,PEI Renjie,WAN Xiaoqiao. 2019. Miocene paleoenvironmental evolution based on benthic foraminiferal assemblages in the Lufeng Sag, northern South China Sea. Acta Oceanologica Sinica, 38(3):124-137
Miocene paleoenvironmental evolution based on benthic foraminiferal assemblages in the Lufeng Sag, northern South China Sea
南海北部陆丰凹陷中新世底栖有孔虫组合与古环境演化研究
Received:September 07, 2018  
DOI:10.1007/s13131-019-1405-7
Key words:South China Sea  Lufeng Sag  Miocene  benthic foraminiferal assemblage  total organic carbon  shelf paleoenvironment
中文关键词:  南海  陆丰凹陷  中新世  底栖有孔虫组合  有机碳  陆架古环境
基金项目:The National Natural Science Foundation of China under contract No. 91328201.
Author NameAffiliationE-mail
XUE Liyuan School of Ocean Sciences, China University of Geosciences, Beijing 100083, China  
DING Xuan School of Ocean Sciences, China University of Geosciences, Beijing 100083, China dingx@cugb.edu.cn 
PEI Renjie School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China  
WAN Xiaoqiao School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China  
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Abstract:
      The Miocene epoch marks the most crucial period during the Cenozoic cooling trend, characterized by the Middle Miocene Climatic Optimum (MMCO) and a series of short-lived cooling events (Miocene isotope events). To understand the paleoenvironmental evolution along the shallow water shelf in the South China Sea during the Miocene, the benthic foraminiferal assemblage and total organic carbon content (TOC) were analyzed at Hole LF 14 located in the Lufeng Sag, northern South China Sea. Three benthic foraminiferal assemblages (e.g., the Uvigerina spp. assemblage, the Cibicides spp. assemblage, and the Cibicidoides spp. assemblage), corresponding to different watermass conditions, were recognized based on Q-mode factor analysis. Early studies suggested that Hole LF14 was deposited under semienclosed bay, middle to outer shelf or even upper bathyal environment during~18.7-4.53 Ma. The dominant Uvigerina spp. assemblage was characterized by low diversity and shallow infaunal to infaunal species, indicating a warm, low-oxygenation and eutrophic conditions since the Early Miocene to MMCO (~18.7-14.24 Ma). An abrupt sea level drop and significant faunal changes were recorded during 14.24-13.41 Ma, suggesting development of the East Antarctic Ice Sheets, which resulted in a drop of sea level and change in benthic foraminiferal assemblages along the shallow water shelf. Beyond the Uvigerina spp. assemblage, the Cibicides spp. assemblage became important during the middle-late Middle Miocene (14.24-11.54 Ma). This assemblage was dominated by epifaunal species with relative high diversity, suggesting high-energy, high-oxygenation and oligotrophic conditions with episodic supply of organic food. The dominant Cibicidoides spp. assemblage with high diversity, indicates a mesotrophic conditions with relative high-oxygen content during the Late Miocene to Pliocene (11.54-4.53 Ma). The appearance and continuous occurrence of Ammonia spp. and Pseudorotalia spp. since 10.02 Ma, may reflect the influence of the Kuroshio Current.
中文摘要:
      中新世是新生代全球气候变冷的一个关键时期,其中以中新世气候最佳期(Middle Miocene Climatic Optimum,MMCO)和一系列短暂的变冷事件(Mi–events)备受关注。南海北部陆丰凹陷LF14井底栖有孔虫组合记录了中新世期间的古海洋环境演化历史。对LF14井171个样品中的底栖有孔虫变量的Q型因子分析结果揭示了3个不同的底栖有孔虫组合,分别是Uvigerina spp.组合,Cibicides spp.组合和Cibicidoides spp.组合。早期研究表明LF14井在早中新世–上新世期间(~18.7–4.53Ma)由半封闭海湾环境转为中–外陆架环境,并一度达到上陆坡环境。早中新世至中新世气候最佳期(~18.7–14.24 Ma),研究区以多样性低和内生–浅内生种为特征的Uvigerina spp.组合占据优势地位,表明研究区处于温暖、低氧和富营养的水体环境。随后,古水深和底栖有孔虫属种在14.24–13.41 Ma期间发生明显变化,表明东南极冰盖在此期间的大规模扩张导致了浅海陆架区海平面下降和底栖有孔虫组合的改变。中中新世中–晚期(14.24–11.54 Ma),以表生种和多样性较高为特征的Cibicides spp.组合成为优势组合,表明研究区水体环境具有高能,高氧和有机质间歇性输入的贫营养特征。进入到晚中新世(11.54–4.53 Ma),以多样性高为特征的Cibicidoides spp.组合成为优势组合,表明研究区处于相对富氧的中等营养环境。其中,Ammonia spp.和Pseudorotalia spp.在10.02 Ma后的大量且连续出现可能指示了研究区可能受到黑潮的影响。
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