Environmental context for the terminal Ediacaran biomineralization of animals
Environmental context for the terminal Ediacaran biomineralization of animals
复制标题
动物埃迪卡拉末期生物矿化的环境背景
DOI：
10.1111/gbi.12178
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发表时间：
2016-07-01
期刊：
影响因子：
3.7
通讯作者：
Martin, A. J.
中科院分区：
文献类型：
--
作者：
Cui, H.;Kaufman, A. J.;Martin, A. J.
在中国南缘埃迪卡拉末期地层中，在灯影组重复灰岩相古生物从Conotubus到Cloudina的转变过程中，保留了钙质生物矿化的开始。这两块化石的大小、漏斗-漏斗结构和底栖生物生活方式相似，但Cloudina是生物矿化的，而Conotubus不是。为了为这一演化里程碑提供环境背景，我们对富含化石的高家山段进行了高分辨率的元素和稳定同位素研究。与Cloudina的首次出现一致的是显著的正碳酸盐碳同位素漂移(高达+6‰)和黄铁矿丰度和34S组成的增加。相反，碳酸盐伴生硫酸盐的δ34S值在整个序列中保持稳定，导致该段下半部硫同位素分馏异常大(>；70‰)。分馏趋势可能与微生物群落的变化有关，硫的歧化作用在下层参与，而微生物硫酸盐还原是上层的主要代谢途径。我们推测，耦合的古生物和生物地球化学异常可能与陆源硫酸盐、碱度和营养物质向沉积盆地的风化通量增加相吻合，这刺激了初级生产力、氧最小带的扩展，以及潮下和盆地环境中优辛条件的发展。有机质的增加生产和埋藏直接与碳同位素异常有关，并可能促进黄铁矿化成为Conotubus和其他软体Ediacara生物群的主要挖掘途径。我们的研究表明，来自捕食的生态压力和来自海水碱度增加的环境压力的融合，为一种前所未有的地质生物学反应奠定了基础：动物生物矿化的进化新颖性。
In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel‐in‐funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high‐resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and 34S composition of pyrite. In contrast, δ34S values of carbonate‐associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft‐bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.