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云南昆明寒武纪早期浅水相磷块岩的氧化还原环境及成因机制
投稿时间:2020-07-13  修订日期:2020-09-12  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2021046
摘要点击次数: 85
全文下载次数: 90
作者单位地址
杨兵 中国地质调查局自然资源实物地质资料中心 河北省三河市燕郊开发区燕灵路245号
金承胜 云南大学古生物重点实验室
云南大学古生物重点实验室 
刘欣 中国地质调查局沈阳地质矿产研究所 
韦一 华北科技学院安全工程学院 河北省三河市燕郊开发区学院街467号
基金项目:国家自然科学基金(No. 41702366, 41902027)、中央高校基本科研业务费(No.3142018025)和云南省基础研究计划项目面上项目(2019FB143)
中文摘要:磷是重要的营养元素,与古环境和生命演化密切相关。在埃迪卡拉纪-寒武纪之交,伴随着骨骼化动物的辐射,华南甚至全球广泛沉积了大量磷酸盐,这暗示磷是古环境的变化与生命演化之间关系的桥梁。然而,目前,磷块岩的沉积环境和形成机制尚不明确。为了探究磷酸盐富集的沉积环境和形成机理,本文研究了华南寒武纪早期梅树村剖面磷块岩的磷酸盐聚集形式、黄铁矿形态学和稀土元素。磷块岩主要是由结晶氟磷酸钙、隐晶质氟磷酸钙和铁氧化物组成。稀土配分模式均为“帽型”配分模式,与沉积物中铁-锰还原带之中的稀土配分模式类似,表明稀土元素遭受了早期成岩的影响。磷块岩中没有草莓状黄铁矿和较低的Ce负异常(Ce/Ce*=0.50~0.82,平均值为0.70),暗示磷块岩沉积于氧化/次氧化的沉积环境。Eu元素未发生异常(Eu/Eu*=0.92~1.08,平均值为0.98),暗示磷块岩可能未受到热液作用的影响。较高的Y/Ho比值(55.3~74.5,平均值为63.6),与海水Y/Ho比值相似,表明磷块岩来源于海水。鉴于华南寒武纪早期广泛的氧化事件、缺氧分层的海水化学结构和上升流活动,本文认为磷块岩的形成源于氧化背景下较高的磷酸盐浓度和深部还原环境中的磷酸盐随上升流活动携带至氧化-次氧化浅水区域。
中文关键词:结晶氟磷酸钙,磷块岩,稀土元素,氧化还原状态,扬子地台
 
Redox environment and formation?mechanism of phosphorite in the early Cambrian shallow shelf, South China
Author NameAffiliationAddress
YANG Bing China Geological Survey Cores and Samples Centre of Natural and Resources 河北省三河市燕郊开发区燕灵路245号
JIN Chengsheng YunnanKeyLaboratoryforPalaeobiology,YunnanUniversity 
LIU Xin China Geological Survey Shenyang institute of Geology and Mineral Resources 
WEI Yi School of Safety Engineering,North China Institute of Science and Technology 河北省三河市燕郊开发区学院街467号
Abstract:Phosphorus is one of the key nutrient elements, which are well associated with sedimentary environment and life evolution. Widespread depositions of phosphorites are coeval with the radiation of skeletonized animals during the Ediacaran-Cambrian transition in South China and global elsewhere, suggesting the good bridge of phosphorus between the sedimentary environment and life evolution. However, sedimentary environment and forming mechanism of phosphorites remain elusive. In order to explore these problems, we conduct aggregation form of phosphate, pyrite morphology, and the composition of rare earth elements (REE) of phosphorites during the early Cambrian Meishucun profile, South China. Our results show that phosphorites are mainly composed of crystalline calcium fluorophosphates, cryptocrystalline calcium fluorophosphates, and iron oxides. The distribution of REE belongs to “hat type” mode, similar to that in the pore-water ferruginous-manganous zone, suggesting that REE is significantly affected by early diagenesis. The absence of framboid pyrite and relatively low Ce/Ce* (0.50~0.82, average 0.70), suggesting that phosphorites are deposited under oxic/dysoxic conditions. The lacking of Eu abnormality (0.92~1.08, average 0.98), indicating phosphorites are not influenced by hydrothermal activity. High Y/Ho ratios of 55.3~74.5 (average 63.6) similar to those of seawater reflect that phosphate is originated from seawater. In combination with widespread oceanic oxygenation, anoxic stratified ocean structure, and intensive upwelling, we infer that phosphorites result from high oceanic phosphate concentrations associate with oceanic oxygenation event and the large fluxes of enriched phosphate contents in reducing deep waters to oxic/dysoxic surface waters by intensive upwelling.
keywords:calcium fluorophosphate, phosphorite, rare earth element, redox conditions, Yangtze Platform
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