寒武纪早期磷酸盐化特异埋藏的微生物化石及其地质意义

The study on microbial fossils and related geological process has become a research hotspot in geoscience recently. However, similar study focusing on the early Cambrian period in China is not fully developed, restricted by research subjects and methods. In Kuanchuanpu Biota (Terreneuvian Series, Fortunian Stage), located in Southern Shaanxi, China, we discovered abundant and varied types of microbial fossils and relevant microstructures, preserved by exceptional phosphatization. Those new materials, combined with multiple analysis techniques, would shed new light on some subjects such as the microbial taxonomy and ecology, the relationship between microorganisms and environment, the influence of microbial actions in the exceptional phosphatization and fossilization. This project is trying to address the taxonomy and ecological role of fossilized microorganisms more accurately, with the help of geometric morphometrics, geochemistry and observation of anatomical structures. Meanwhile, we will analyze microbial effects and the mechanism of phosphatizing by examining ultra-microstructures of such fossils in this type of Lagerstätte. Especially, we present “microbial pseudomorphs”, which is a new pathway to preserve non-mineralized animal bodies. Analyzing their forming mechanism and the attempt to replicate such structures in contemporary taphonomy experiments, will not only expand the category of Lagerstätte with exceptionally phosphatized fossils, but also increase the chance for us to retrieve non-mineralized animals in deeper time. Although they are soft and hardly preserved conventionally, they could be pseudo-morphed under some particular circumstances.

微生物化石与微生物地质作用是当前地球科学的热点与前沿课题之一，而我国在寒武纪早期这一关键地质历史时期的相关研究尚不深入，研究对象和研究方法还有较大局限。我国陕南寒武纪纽芬兰世幸运期的宽川铺生物群中，近年来发现了丰富多样的磷酸盐化特异埋藏微生物化石与相关显微结构，结合多种新的技术手段，有望解决部分涉及微生物的分类与生态、微生物与环境的关系、微生物作用与磷酸盐化特异埋藏机制等方面的问题。本项目拟综合形态测量学、地球化学、内部微观形态等新角度，更准确地辨识不同的微生物类群，在此基础上分析当时的微生物生态。并且结合埋藏学与化石超微结构研究，探索在此类化石库中微生物作用对磷酸盐化过程的影响。针对新发现的非矿化动物躯体保存模式——微生物假形，讨论其生成机制并尝试进行埋藏学实验模拟，不仅有望拓展磷酸盐化特异埋藏化石库的内涵，也为在更早的地史时期发现非矿化的动物躯体化石提供新的可能。

本项目主要通过非矿化动物体的微生物假形这一关键化石记录，系统进行了相关的微生物形态与生物分类学，微生物作用与动物个体假形的形成机制，软躯体埋藏保存以及以假形保存的未知类型微体动物的生物属性和分类演化几个方面的研究。研究揭示了在寒武纪早期，存在多样的微生物群落，可以快速侵入并交代微体动物的躯体轮廓，形成较为完整的动物个体假形化石。进一步研究表明，这些微生物可能主要与革兰氏阴性的变形菌类相关，丰富了对这一关键地史时期微生物生态的认识。而相关的动物个体表保留下来的轮廓形态和躯体构型信息，说明了早在寒武纪最初期，原始的后生动物，特别是两侧对称动物已经有了一定程度的发展和分化。同时在研究过程中，通过对比不同时期和不同地域剖面的化石类群的演替状况，以计算流体力学模拟的手段探索微体底栖生物的形态差异——个体生态特征——栖息环境适应性之间的关系，证明了微体动物的形态差异导致的流体动力学效应可能也是影响其演化的一个因素。此外，鉴于微体化石数量浩繁，人工挑选效率很低，难以满足研究深入发展的需求。因此尝试开发微体化石的人工智能识别系统，目前已经在软件层面取得了人工智能图像识别技术应用于微体化石领域的初步成果。对微体化石的识别准确率和对训练化石的数量要求都有明显改善。