贵州瓮安生物群球状化石原位元素地球化学特征及其对成磷作用的指示

Geochemical characteristics of in situ elements in spherical fossils from Weng’an biota in Guizhou and their indications for phosphorization

贵州瓮安-福泉磷矿区埃迪卡拉系陡山沱组上磷矿段(b矿层)产出一类特殊的微体化石组合,称为瓮安生物群,其中含大量种类丰富的球状化石,但以往研究多侧重于球状化石本身,缺乏对球状化石与成磷作用关系等的深入研究。为此,本研究运用光学显微镜、超景深显微镜、扫描电镜-能谱(SEM-EDS)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)等方法对其原位元素分布、主量元素以及微量元素的地球化学特征进行研究。结果显示,瓮安生物群球状化石均已胶磷矿化,且较高的P_(2)O_(5)含量(30.13%~44.92%,平均43.17%)表明其普遍经历了成磷作用;V/Cr平均值小于2、Ce负异常明显、Ce_(anom)小于-0.1,指示其成磷作用的环境为氧化环境;稀土元素PAAS分配模式图呈“帽型”,反映生物参与成磷作用并发挥了重要作用。

There is a special kind of microfossil group produced in the upper phosphate ore section(b ore layer)of Edicaran Doushantuo Formation in Weng’an-Fuquan phosphate mining area of Guizhou,known as the Weng’an biota,which contains a large variety of abundant spherical fossils.However,previous studies have mostly focused on the spherical fossils themselves,lacking in-depth research on the relationship between spherical fossils and phosphorization.Therefore,this study employs optical microscopy,extended depth of field microscopy,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),and laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)to investigate the distribution of in situ elements and the geochemical characteristics of major and trace elements.The results show that the spherical fossils of the Weng’an biota have undergone the formation of collophane and their high P_(2)O_(5)content(30.13%~44.92%,average 43.17%)indicates the occurrence and widespread presence of phosphorization.The average V/Cr ratio,which is less than 2,the significant negative Ce_(anom)aly,and the Ce_(anom),which is less than-0.1,indicate an oxidizing environment of phosphorization.The PAAS distribution pattern of rare earth elements exhibits a“hat-like”feature,reflecting that organisms were involved in and played an important role in the phosphorization.