川南威远地区早寒武世氮循环及古环境意义  

Nitrogen Cycle and Paleoenvironmental Implications in the Weiyuan Area,Southern Sichuan During the Early Cambrian

作　　者：曹光耀 刘宇 侯明才[1,3,4] 陈安清[1,3] 徐胜林[1,3] CAO GuangYao;LIU Yu;HOU MingCai;CHEN AnQing;XU ShengLin(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;International Center for Sedimentary Geochemistry and Biogeochemistry Research,Chengdu University of Technology,Chengdu 610059,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China;Key Laboratory of Deep-time Geography and Environment Reconstruction and Applications of Ministry of Natural Resources,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]成都理工大学沉积与生物地球化学国际研究中心,成都610059 [3]成都理工大学油气藏地质及开发工程国家重点实验室,成都610059 [4]成都理工大学深时地理环境重建与应用重点实验室,成都610059

出　　处：《沉积学报》2024年第6期2031-2041,共11页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41802122,42050104,42272132)。

摘　　要：【目的】寒武纪早期是地质历史时期海洋环境演化的重要时期,深入探究该时期海洋氧化还原及氮循环演化有助于厘清同期有机质富集的主控因素。【方法】以川南威远地区筇竹寺组为研究对象,系统开展铁组分、氮同位素、硫同位素分析。【结果】威远地区在寒武纪早期,海洋环境响应同期海平面波动,氧化还原条件经历了多次转变。在寒武纪第二期,深部缺氧硫化水体扩张至浅水陆架环境,强烈的反硝化作用导致海水中的NO-3持续被消耗,最终导致威远地区海洋氮循环以生物固氮为主。同时,较低的δ15N值暗示寒武纪第二期相对较低的初级生产力水平。在寒武纪第三期,显著升高的δ15N值表明海洋NO-3库逐渐扩大,表层氧化海水逐步扩张。【结论】沉积环境的氧化还原条件是威远地区筇竹寺组有机质富集的主要控制因素。由海侵引起的强烈缺氧条件导致筇竹寺组产生三次显著的有机质富集。海平面的变化最终影响着寒武纪早期华南内陆架地区的氧化还原、氮循环演化及有机质富集。[Objective]The early Cambrian was a pivotal period of oceanic environmental evolution in Earth history.To grain the insight into evolutions of oceanic redox condition and nitrogen cycle,which can favor to ascertain the dominant control on coeval organic matter enrichment.[Methods]The present study conducted the iron speciation,nitrogen and sulfur isotopes analyses for the Qiongzhusi Formation in the Weiyuan area.[Results]The oceanic redox condition experienced several transitions in response to coeval sea-level fluctuations during the early Cambrian.In the Cambrian Age 2,the deep euxinic watermasses expanded to the shallow-water shelf environment,and intense denitrification resulted in the persistent consumption of NO-3 in seawater,which eventually caused the nitrogen cycle dominated by biological nitrogen fixation.Synchronously,the lowδ15N values imply the relatively low primary productivity level in the Cambrian Age 2.The obviously increasedδ15N values in the Cambrian Age 3 suggest the stepwise expansion of NO-3 reservoir and extension of surface oxygenated seawater.[Conclusions]The organic matter enrichment of the Qiongzhusi Formation in the Weiyuan area was dominantly controlled by redox conditions in the sedimentary environment,where the severe anoxia caused by transgression resulted in three significant organic matter enrichments.The redox conditions,nitrogen cycle,and enrichment of organic matter in inner shelf environments of South China were influenced by sea-level eustacy during the early Cambrian.

关 键 词：筇竹寺组 氮同位素 铁组分 氧化还原 有机质 

分 类 号：P597[天文地球—地球化学]