徐淮地区新元古代九顶山组燧石结核的地球化学特征  

GEOCHEMICAL CHARACTERISTICS OF THE CHERTS OF THE NEOPROTEROZOIC JIUDINGSHAN FORMATION IN NORTHERN JIANGSU AND ANHUI PROVINCES

作　　者：严贤勤[1] 孟凡巍[1] 袁训来[1] 

机构地区：[1]中国科学院南京地质古生物研究所,南京210008

出　　处：《微体古生物学报》2006年第3期295-302,共8页Acta Micropalaeontologica Sinica

基　　金：国家自然科学基金(批准号:40472003);科学技术部重大国际合作项目(2003CB716805);国家重点基础研究发展规划项目(G200007701);中国科学院知识创新基金(KZCX3-SW-141)的经费支持

摘　　要：徐淮地区新元古代九顶山组燧石结核中保存有很好的丝状、球形蓝藻和细菌化石。为了探讨其化石化过程和沉积环境,我们利用地球化学方法对燧石结核进行了分析,结果显示,该燧石结核中Al/(Al+Fe+Mn)值为0.127—0.383,平均0.247;Ti O2和Al2O3含量较低;与地壳克拉克值相比,Ba,Co,Nb,Cu,Be,V,Sr,Ni相对亏损,Ti,Cr,Mn强烈亏损。稀土元素总量低,轻稀土元素大于重稀土元素;具弱的Ce负异常和较明显的Eu正异常,北美页岩标准化模式曲线呈平坦状或右倾。这些地球化学特征反映了九顶山燧石结核形成于离大陆较近的边缘浅海碳酸盐台地沉积环境,在其形成的过程中伴有海相热液的作用。化石的保存与Si O的快速沉积和硅化有关。Chert nodules containing abundant well preserved microfossils （e. g. , filamentous and coccoid cyanobacteria）, occur in the upper parts of the Neoproterozoic Jiudingshan Formation in northern Jiangsu and Anhui provinces. Here we use geochemical data to discuss the formation of Jiudingshan cherts, especially the SiO2 source of the Jiudingshan cherts, as well as its sedimentary environment. The cherts of the J iudingshan Formation have low AI/（Alq-Fe q-Mn） ratios （ranging from 0.127 0.383, with average0.247）, and low MnO2 and AI2O3 contents, both of which reflect the effect of marine hydrothermal activity. The contents of Ba, Co, Nb, Cu, Be,V, Sr and Ni are relatively low compared to their Clarke values; the contents of Ti, Cr and Mn are much lower than their Clarke values. The MnO/TiO2 ratios of the Jiudingshan cherts, ranging from0.034 0.224 and averaging0.127, indicate that the cherts were probably deposited in the continental slope and/or marginal sea basin. The Σ,REE values of the Jiudingshan cherts are very low （2. 396 8. 330 ppm, with average 4. 885ppm）,ΣLREE/ΣHREE raiios are more than 1 ;3Ce and 3Eu values range from 0. 901 to 1. 060 and 0. 948 to 2. 686, averaging 0. 952 and 1. 667, respectively. The North American shale-normalized REE distribution patterns also indicate that the formation of the Jiudingshan cherts has close relationship with marine hydrothermal activity.

关 键 词：新元古代 九顶山组 燧石结核 地球化学特征 徐淮地区 

分 类 号：Q911[天文地球—古生物学与地层学]