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A geochemical study of the Ediacaran discoidal fossil Aspidella preserved in limestones: Implications for its taphonomy and paleoecology.
Geobiology ( IF 3.7 ) Pub Date : 2017-04-11 , DOI: 10.1111/gbi.12240
N Bykova 1, 2 , B C Gill 1 , D Grazhdankin 2, 3 , V Rogov 2 , S Xiao 1
Affiliation  

The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three‐dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyr, and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13Corg values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide‐oxidizing bacteria. δ13Ccarb, δ18Ocarb, and δ34Spyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non‐euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion.

中文翻译:

石灰岩中保存的Ediacaran盘状化石Aspidella的地球化学研究:其拓朴学和古生态学意义。

Ediacara生物群的特征是在寒武纪爆炸发生之前宏观复杂生命的上升。盘状化石Aspidella是埃迪卡拉生物区系中数量最多,分布最广泛的元素之一,其被解释为是地下固定物,可能锚定了菱形表皮生物。它是一种形态简单的化石,主要保存在硅质碎屑岩中,不适合用于进行全面稳定的同位素地球化学分析以破译其拓扑学和古生态学。在这方面,三维保存的Aspidella西伯利亚北部Olenek隆起的Khatyspyt组上层Ediacaran石灰岩中的化石提供了难得的机会,可以利用地球化学来了解其分类学和古生态学。要充分利用这个机会,我们分析δ 13 C ^碳水化合物,△ 18 Ø碳水化合物,δ 13 Ç组织,δ 34小号PYR和Khatyspyt铁形态Aspidella化石和周围的沉积物矩阵,以便调查他们是否托管微生物共生,它们如何化石以及其生态环境的氧化还原条件。曲霉固着器和周围的沉积物矩阵显示没有区别δ 13 Ç有机值,这表明它们没有主机和从微生物共生体,例如甲烷,甲基营养,或硫化物-氧化细菌衍生营养素显著量。δ 13 Ç碳水化合物,δ 18 ö碳水化合物,和δ 34个小号PYR数据,与岩相意见一起,表明微生物硫酸盐还原促进的保存Aspidella通过在基体胶结和沉积物压实之前在固着物中促进早期自生方解石胶结。铁形态数据是模棱两可的,主要是因为总铁浓度低。但是,考虑到已发表的硫同位素和生物标志物数据,表明Aspidella可能生活在非富余水域中。古环境有利时,Aspidella可能是一种机会生物,在海底大量繁殖。这项研究表明,石灰岩中保存的埃迪卡拉安化石的地球化学数据可以为生活在寒武纪爆发前夕的这些神秘生物的分类学和古生态学提供重要见解。
更新日期:2017-04-11
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