Abundant metazoans phyla made their first appearances in the fossil record during a relatively short time span in the Ediacaran-Cambrian interval (560–520 Ma) and rapidly expanded ecologically during the early Cambrian, leading to the establishment of metazoan-dominated ecosystems accompanied by widespread biomineralization. This unique evolutionary event was known as the ‘Cambrian Explosion’. Although a significant amount of work has been undertaken to understand the evolution of life during this time interval, previous studies have mainly focused on fossil records from the Cambrian fine-grained clastic rocks deposited in shallow-water environments. However, fossil records from marlstones and mudstones formed in deep-water basins were poorly understood.

In this study, we focus on fossil records from the black thin-bedded marl and calcareous mudstones of the lower Cambrian Shuijingtuo Formation in the Three Gorges area, Hubei Province. A total of 9059 fossil specimens, including both microfossils and megafossils belonging to 45 species and 14 major taxonomic groups were recovered from the Shuijingtuo Formation at the Luojiacun section. Four palaeoecological assemblages were recognized based on fossil composition and ecological characteristics. The oldest assemblage (Assemblage A) features an Isoxys-dominated planktonic community with only one benthic group of bradoriids and exhibits the highest fossil abundance and lowest species diversity. Assemblage B is characterized primarily by highly diverse benthic groups, which in decreasing order of abundance include bradoriids (27.4%), sponge spicules (9.8%), cnidarians (5.7%) and hyoliths (2.0%). The third assemblage (Assemblage C) introduces the predominant role of sponge spicules, which compose 44.8% of the community. In contrast, Assemblage D is predominated by phytoplankton featuring the lowest fossil abundance and low diversity. Integration with geochemical and sedimentary data indicates that these biotic assemblages and their evolution were mainly controlled by environmental redox variations and changes in terrestrial fluxes and water depth, subsequently suggesting a significant role of these factors on biotic evolution in the early Cambrian deep-water environment. This study provides support for the importance of oxygen levels in the evolution of life during the early Cambrian.

在Ediacaran-Cambrian间隔（560-520 Ma）的相对短时间内，大量的后生动物门在化石记录中首次出现，并在寒武纪早期迅速地生态扩展，从而导致了以后生动物为主的生态系统的建立，并伴随着广泛的生物矿化。这个独特的进化事件被称为“寒武纪爆炸”。尽管已经进行了大量工作以了解在此时间间隔内生命的演变，但是以前的研究主要集中在沉积在浅水环境中的寒武纪细粒碎屑岩的化石记录上。但是，人们对在深水盆地中形成的泥岩和泥岩的化石记录了解甚少。

在这项研究中，我们重点研究湖北三峡地区下寒武统水井tu组下部黑色薄层泥灰岩和钙质泥岩的化石记录。从罗家村段水井tu组共采集到9059个化石标本，包括属于45个物种和14个主要分类群的微化石和巨型化石。根据化石成分和生态特征，识别出四种古生态组合。最古老的组合件（组合件A）具有异氧基的浮游生物群落中，只有一个底栖类的Bradoriids，并且显示出最高的化石丰度和最低的物种多样性。组合物B的主要特征是底栖动物种类繁多，其丰富程度从高到低依次包括Bradoriids（27.4％），海绵针（9.8％），cnidarians（5.7％）和Hyoliths（2.0％）。第三个组合（组合C）介绍了海绵针的主要作用，海绵针占社区的44.8％。相反，组合物D以浮游植物为主，其化石丰度最低且多样性较低。与地球化学和沉积数据的整合表明，这些生物组合及其演化主要受环境氧化还原变化以及地面通量和水深的变化控制，随后表明这些因素在早期寒武纪深水环境中对生物演化的重要作用。这项研究为氧水平在寒武纪早期生命演化中的重要性提供了支持。