新元古代末期钙化蓝细菌、钙化藻类繁盛及其环境背景

There is a paradox which puzzled the geologists a great deal, comparing with their widespread in the Palaeozoic, calcified cyanobacteria were so scarce or even absent until the Neoproterozoic. If seawater saturation state with respect to CaCO3 minerals was high during much of the Proterozoic, then why was cyanobacterial calcification so poorly developed in comparison to the Palaeozoic? Attempts to account for this, was dubbed the ‘Precambrian Enigma’. Try to solve this problem, many theories were presented, including changes in seawater chemistry, reduced pH buffering and elevated saturation state, and also enhanced a biological adaptations, CO2 concentrating mechanisms (CCMs) . Gaojishan Fauna, a weakly and also the earliest skeleton animal group at the terminal Ediacaran Dengying Formation, is so special and represented by fossils such as Cloudina、Sinotubulites、Conotubus、Gaojiashania、Shaanxilithes，therefore may recorded a tubular animal evolutionary event. unexpectedly, accompanied with this tubular fossils, a diversified group of calcified cyanobacteria like Spirellus Eiphyton， Girvanella， Cambricodium, and also many new calcified fossil algae are detected, which opens up a welcome new window to disclose the co-evolution biomineralzing of animals and plants. This program aims to better understand the origin of mineralized animals and coherent diversification of calcified cyanobacteria and algae, as well as the relationship between geochemistry of early evolution and environmental background through a comparative study of multiple geochemical indicators (C, O, Fe, isotope geochemistry, trace elements, major elements and petrography).

钙化的蓝细菌在新元古代只有零星发现，至古生代早期才广为展布，这一现象困扰了很多科学家，被学者们称为“前寒武纪之谜”。 很多学者都试图破解这一谜团，解释包括:前寒武纪碳酸钙过的饱和所导致的微晶碳酸钙矿物晶体（<4μm）大量沉淀，阻止了蓝细菌的矿化;前寒武纪蓝细菌可能不具备钙化的功能 , 因而不易保存为化石，只有进入了早寒武世它们才获得了钙化功能 ,并认为这与早寒武开始类型多样的钙化蓝细菌在地层中大量出现的地质记录相吻合。可喜的是在新元古代末期，伴随着最早骨骼生物群-高家山生物群的出现，申请者及其团队发现了大量钙化蓝细菌和钙化藻类化石，这一发现极大的弥补了国内外新元古代末期矿化藻类资料的空缺，同时证明动物与植物存在着协同演化关系。近来的研究表明与这一生物矿化事件同时，海洋环境条件发生了明显波动。高家山生物群中钙化蓝细菌类、多门类钙化藻类的发现及其环境研究可能成为我们打开“前寒武纪之谜”的金钥匙

寒武纪大爆发引人注目，但埃迪卡拉纪末期生物多样性面貌尚未有清晰和统一的认识。本项目紧紧围绕核心科学问题，针对新元古代生物和生态系统多样性，钙化藻类和弱矿化骨骼类型的起源及辐射演化及其协同关系进行了较为系统的研究，课题组成员发表标注项目的学术论文 14 篇，其中国际SCI论文8 篇，研究取得了如下重要进展：.1. 在系统化石生物学研究的基础上，重建了“高家山生物群”的生物多样性和古生态学面貌，认为新元古代末期存在着管状生物的大辐射，生态系统已显示一定的多样性。.2. 首次在埃迪卡拉纪末期发现了形态多样的钙化蓝细菌化石类群，鉴定出5属8种，钙化蓝细菌和钙化藻类化石在新元古代末高家山生物群中的发现证实寒武纪与前寒武纪生物界之间存在明显的连续性;这一发现也极大的弥补了国内外新元古代末期矿化藻类资料的空缺。这一矿化生物群的发现，同时证明动物与植物存在着协同演化关系。.3. 寒武纪大爆发之前的骨骼生物多样性，研究表明一些埃迪卡拉纪骨骼类群可能已经扩展到早寒武纪，这这两个类群之间存在进化的连续性。

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