Controls on fossil pyritization: Redox conditions, sedimentary organic matter content, and Chuaria preservation in the Ediacaran Lantian Biota
Controls on fossil pyritization: Redox conditions, sedimentary organic matter content, and Chuaria preservation in the Ediacaran Lantian Biota
复制标题
化石黄铁矿化的控制：埃迪卡拉蓝田生物群中的氧化还原条件、沉积有机质含量和 Chuaria 保存
DOI：
10.1016/j.palaeo.2016.05.013
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发表时间：
2017-05-15
影响因子：
3
通讯作者：
Ouyang, Qing
中科院分区：
文献类型：
--
作者：
Guan, Chengguo;Wang, Wei;Ouyang, Qing
黄铁矿化是软组织特殊保存的主要埋藏途径。虽然各种埃迪卡拉纪Lagerstatten包含黄铁矿化的化石，控制这个埋藏途径之前，前寒武纪-中生代过渡最近才得到了极大的关注，还没有研究彻底调查环境条件，促进异常保存通过黄铁矿化在早期埃迪卡拉纪。本文利用岩相学、电子显微镜和地球化学资料，对华南早埃迪卡拉纪蓝田组中的宏观化石Chuaria的形成环境进行了研究。Chuaria以普遍黄铁矿化（球状）的球状和非普遍黄铁矿化（盘状）的亚球状化石出现在不同的地层间隔中。虽然这些不同的地层间隔是相似的总硫（TS，类似于5%），亚球状Chuaria页岩有更大的总有机碳（TOC，类似于7.9%）比球状Chuaria页岩（类似于3.6%）的内容。此外，岩相学观察和TOC-TS交叉图表明，而球状化石保存在亚氧底沃茨，亚球状化石保存在缺氧底沃茨。总体而言，这些结果证实，黄铁矿化在前寒武纪一般有利于有机贫，活性铁丰富，硫酸盐丰富的环境可能与缓慢的沉积速率。当有机物是稀缺的，活性铁是丰富的，细菌硫酸盐还原（BSR）产生硫化氢和活性铁浓度梯度周围的化石，这在动力学和动力学上有利于快速和普遍的黄铁矿化，在球状Chuaria观察。相反，当有机物丰富和活性铁/硫酸盐的可用性受到广泛的BSR的限制，化石被相对迅速地埋藏在沉积物的BSR代谢带，在那里他们主要保存为铝硅化的碳质化石，被压实成亚球状的形式。因此，埃迪卡拉纪黄铁矿化化石之间的差异可能反映了沉积有机质含量和/或底层水氧化还原化学的差异。(C)2016爱思唯尔B. V.保留所有权利。
Pyritization represents a major taphonomic pathway for exceptional preservation of soft tissues. Although various Ediacaran Lagerstatten contain pyritized fossils, the controls on this taphonomic pathway prior to the Precambrian-Phanerozoic transition have only recently received significant attention, and no studies have yet thoroughly investigated environmental conditions facilitating exceptional preservation via pyritization in the early Ediacaran. Here, we investigate the preservational environments of macroscopic fossil Chuaria in the early Ediacaran Lantian Formation of South China using petrographic, electron microscopic, and geochemical data. Chuaria occur as pervasively pyritized (spheroid-shaped) globose and non-pervasively pyritized (disk shaped) subglobose fossils in different stratigraphic intervals. Although these different stratigraphic intervals are similar in terms of total sulfur (TS, similar to 5%), subglobose Chuaria shales have greater total organic carbon (TOC, similar to 7.9%) contents than globose Chuaria shales (similar to 3.6%). Additionally, petrographic observations and TOC-TS cross-plots suggest that, whereas globose fossils were preserved under suboxic bottom waters, the subglobose fossils were preserved in euxinic bottom waters. Overall, these results affirm that pyritization in the Precambrian was generally favored in organic-poor, reactive iron-rich, sulfate-rich environments probably with slow sedimentation rates. When organics were scarce and reactive iron was abundant, bacterial sulfate reduction (BSR) created hydrogen sulfide and reactive iron concentration gradients around fossils, which kinetically and thermodynamically favored rapid and pervasive pyritization, as observed in globose Chuaria. Conversely, when organics were abundant and reactive iron/sulfate availabilities were limited by widespread BSR, fossils were relatively rapidly buried beneath the BSR metabolic zone of sediment, where they were principally preserved as aluminosilicified carbonaceous fossils that were compacted into subglobose forms. Thus, preservational variations among pyritized fossils in the Ediacaran may reflect differences in sedimentary organic matter content and/or bottom water redox chemistry. (C) 2016 Elsevier B.V. All rights reserved.