华南埃迪卡拉纪晚期深水相氮循环过程重建  

Reconstruction of Deep-Water Nitrogen Cycle during the Late Ediacaran in South China

作　　者：叶凯云 赵坤 童霞 李松倬 郎咸国 Ye Kaiyun;Zhao Kun;Tong Xia;Li Songzhuo;Lang Xianguo(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;Chengdu Exploration and Development Research Institute of PetroChina Daqing Oilfield Co.,Ltd.,Chengdu 610051,China)

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]中国石油大庆油田有限责任公司成都勘探开发研究院,四川成都610051

出　　处：《地球科学》2024年第9期3212-3227,共16页Earth Science

基　　金：国家重点研发计划项目(No.2021YFA0718100)。

摘　　要：重建地质历史时期的古海洋氮循环过程有助于了解当时的海洋氧化还原状态,而目前埃迪卡拉纪晚期的海洋氮循环研究程度较低,因此对桂北泗里口和黔东南上地坪剖面开展了详细的全岩氮(δ15N)和有机碳同位素(δ13C_(org))研究.结果显示,泗里口和上地坪剖面的δ15N平均值分别为(1.6±2.0)‰和(3.5±1.1)‰,总体上均表现为由老到新逐渐降低,两个剖面的δ13_(Corg)平均值分别为(-30.0±1.4)‰和(-30.6±1.4)‰.较高的δ15N值表明该时期为硝化‒反硝化作用相耦合的好氧氮循环,海洋中存在一个稳定的硝酸盐库.研究剖面δ15N值由老到新均表现为逐渐降低,可解释为底层缺氧水体的扩张,反硝化作用和厌氧氨氧化作用消耗了表层水体中大量的NO3‒,刺激了固氮作用.因此,埃迪卡拉纪末期深部缺氧水体的扩张可能加剧了~542 Ma埃迪卡拉生物群的灭绝.The reconstruction of the paleo-ocean nitrogen cycle in geological history is helpful to understanding the REDOX state of the ocean at that time,whereas the study of the Late Ediacaran marine nitrogen cycle is relatively insufficient.Here we report detailed nitrogen isotope(δ15N)and organic carbon isotopic compositions(δ13_(Corg))from the Silikou section in northern Guangxi and the Shangdiping section in southeastern Guizhou Province.The results show that the average values of δ15N from the Silikou section and Shangdiping section are(1.6±2.0)‰and(3.5±1.1)‰,respectively,both of which show a gradual decrease from old to new.The meanδ13Corg values of the two sections are(-30.0±1.4)‰ and(-30.6±1.4)‰,respectively.The relatively highδ15N values indicate that there was an aerobic nitrogen cycle coupled with nitrification and denitrification,and there was a stable marine nitrate reservoir in the Late Ediacaran.The gradual decrease from old to new in δ15N may result from the expansion of deep water anoxia in which denitrification and anammox can consume a large amount of NO_(3)‒and stimulate nitrogen fixation.Thus,the expansion of deep anoxic water column at the end of the Ediacaran may have exacerbated the extinction of the Ediacaran biota at~542 Ma.

关 键 词：氮同位素 埃迪卡拉纪晚期 深水相 华南 地球化学 地层学. 

分 类 号：P597[天文地球—地球化学]