Influence of redox conditions on animal distribution and soft-bodied fossilpreservation of the Lower Cambrian Chengjiang Biota
Influence of redox conditions on animal distribution and soft-bodied fossilpreservation of the Lower Cambrian Chengjiang Biota
复制标题
氧化还原条件对下寒武统澄江生物群动物分布及软体化石保存的影响
DOI：
10.1016/j.palaeo.2018.07.010
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Xianguang Hou
中科院分区：
文献类型：
--
作者：
Changshi Qi;Chao Li;Sarah E. Gabbott;Xiaoya Ma;Luhua Xie;Wenfeng Deng;Chengsheng Jin;Xianguang Hou
保存异常完好的澄江生物群（中国云南）对于理解寒武纪进化辐射期间复杂的动物丰富的生态系统的快速发展具有重要意义。然而，该存款中捕获的化石提供的生态信号可能无法准确反映活体群落，尸体的运输和腐烂是潜在修改的主要过程。主要的含化石层段（玉安山组，毛天山页岩段）由两种不同沉积成因的粘土岩组成：“背景”层代表缓慢的半远洋沉积进入深水沃茨，而“事件”层代表远源浊积岩或风暴生成的层。每种床型都有不同的化石组合和保存模式，强调了解释每种床型古环境的重要性。本文利用铁形态、δ34Spy、δ13Ccarb、δ13CTOC和钼丰度等地球化学指标，对背景层和事件层的古氧化还原条件进行了系统的研究。这些数据来自于澄江化石群中最完整的岩芯，使我们能够区分这些动物生活的氧化还原条件，以及它们被埋葬和异常保存的地方。我们的研究结果表明，背景床占主导地位的dysocompatibility条件，在这里，一个多样化的海绵社区容忍低氧条件下生活。与此相反，事件层起源的较浅的陆架和近岸过渡环境几乎是持续的好氧环境，多样的澄江生物群在这里进行了营养。因此，澄江沉积物记录了背景层和事件层内两种不同的古生物群落。在空间上接近的对比氧化还原条件可能促进了软体化石的保存。我们的发现提供了一个有价值的案例研究，了解生态组成和环境背景下的特殊保护的必要性。
The exceptionally preserved Chengjiang Biota (Yunnan, China) is significant for understanding the rapid development of complex animal-rich ecosystems during the evolutionary radiation of the Cambrian. However, the ecological signal provided by the fossils captured in this deposit may not reflect accurately the in-life community, with transport and decay of carcasses being the principal processes responsible for potential modification. The principal fossil-bearing interval (Maotianshan Shale Member, Yu'anshan Formation) is comprised of claystones of two distinct depositional origins: the “background” beds represent slow hemipelagic deposition into deep waters, while the “event” beds represent distal turbidites or storm-generated beds. Each bed type has a distinct fossil assemblage and preservation mode underscoring the importance of interpreting the palaeoenvironment of each bed type. Here, we interpret palaeo-redox conditions for both the background beds and the event beds by conducting a systematic geochemical study using iron speciation, δ34Spy, δ13Ccarb, δ13CTOC and molybdenum abundance. These data are from the most complete core recovered from the Chengjiang fossiliferous units and allow us to distinguish redox conditions where the animals lived, and where they were buried and exceptionally preserved. Our results demonstrate that background beds were dominated by dysoxic conditions; here, a diverse sponge community tolerant of low-oxygen conditions lived. In contrast, the shallower shelf and offshore-transitional environments, where event beds were sourced, were almost persistently oxic, and it was here where the diverse Chengjiang Biota flourished. Thus, the Chengjiang sediments record two distinct palaeocommunities within the background and the event beds. The contrasting redox conditions in close spatial proximity likely facilitated the soft-bodied fossil preservation. Our findings provide a valuable case study in the necessity to understand ecological composition and exceptional preservation informed by environmental context.