寒武纪早期海洋阶段性氧化驱动早期后生动物多样化进程  

Stepwise Oxygenation of Early Cambrian Ocean Drove Early Metazoan Diversification

作　　者：赵相宽 史晓颖[1,2] 王新强[1,2] 汤冬杰[2,3] Zhao Xiangkuan;Shi Xiaoying;Wang Xinqiang;Tang Dongjie(School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences,Beijing 100083,China;School of Scientific Research,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质大学生物地质与环境地质国家重点实验室,北京100083 [3]中国地质大学科学研究院,北京100083

出　　处：《地球科学》2018年第11期3873-3890,共18页Earth Science

基　　金：国家自然科学基金项目(No.41672336)

摘　　要：伊迪卡拉-寒武纪过渡期是地球历史上海洋环境与生命演化变革的关键时期之一.有研究认为海洋氧化可能是驱动早寒武世动物快速多样化的主要原因,但有关海洋氧化及硫化水体演变过程和发生时间的认识仍有分歧.运用ICP-MS、FESEM、EDS和XRD技术对位于古陆架边缘-斜坡背景的湘西四都坪、黔东松江大桥等剖面牛蹄塘组黑色页岩进行氧化还原敏感元素、黄铁矿形态学、总有机碳及N、P等营养元素丰度变化进行高分辨研究.结果显示,研究区牛蹄塘沉积期底层海水条件经历了复杂的发展过程,表现为3个铁化与3个硫化时段的动态交互,在第3阶晚期转为亚氧化-氧化条件.不同相区的对比表明,海水氧化随时间由浅水向深水区扩展:台地相区发生在第2阶晚期,陆架边缘出现在第3阶晚期,而深水盆地以持续铁化为主,晚期出现硫化,表明海洋氧化界面逐步加深下移.沉积物Mo/TOC,U/TOC值自下而上持续增加,与Cr、Mn、P、N丰度变化趋势一致,表明海水氧化程度逐步增强.主要化石类群的时空分布与海水氧化过程对应良好,表明海洋阶段性氧化与硫化水体消失对后生动物多样化进程有明显的控制作用.Ediacaran-Cambrian transition is a critical period in Earth history, during which both marine environment and life have experienced drastic changes. It is arguably suggested that pervasive oxygenation and associated geochemical changes in the ocean have potentially driven the rapid diversification of Early Cambrian metazoans, however, the timing and process of ocean oxygenation have not been well constrained. In this paper, an integrated study was conducted on the Lower Cambrian Niutitang （NTT） Fm. in Siduping area, West Hunan and Songjiang Bridge area, East Guizhou, which were paleogeographically situated at the shelf margin-upper slope setting of the Yangtze block. Using ICP-MS, FESEM, EDS and XRD techniques, the abundances and patterns of RSE （redox sensitive elements）, pyrite morphology, TOC （total organic carbon）, as well as N, P nutrients were investigated systematically. The results show that during NTT deposition, bottom seawaters in the study area experienced a complicated evolution, with a dynamic alternation of 3 ferruginous and 3 euxinic intervals, and suboxic-oxic condi-tions occurring only at the latest Cambrian Stage 3. Comparison with relevant data published previously from each facies belts within the Yangtze block shows that the seawater oxygenation was a progressive process expanding from shallow water area to deep-water area in time. Platform facies area oxygenated at the late Stage 2, shelf margin area in the late Stage 3, and the deepwater basin kept ferruginous until the latest Stage 3, when it became euxinic. Sediment Mo/TOC, U/TOC ratios increased from bottom to top consecutively in the section, coupled with elevated Cr, Mn, N and P secular trends, likely indicating an overall enhancement of seawater oxygenation. The spatial-temporal distribution and increased paleoecologic complexity of major fossil groups in the Yangtze block over time show a well coincidence with the seawater oxygenation process, likely implying that increased ocean oxygenation and declined euxinic seawater

关 键 词：草莓状黄铁矿 氧化还原敏感元素 海水Mo-U通量 牛蹄塘组 扬子地台 生物地层学 

分 类 号：P736.4[天文地球—海洋地质]