Palaeoenvironmental and ecological interpretation of the trace fossil Rhizocorallium based on contained iron framoboids (Upper Devonian, South China)
Palaeoenvironmental and ecological interpretation of the trace fossil Rhizocorallium based on contained iron framoboids (Upper Devonian, South China)
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DOI：
10.1016/j.palaeo.2016.01.012
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发表时间：
2016-03
期刊：
影响因子：
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通讯作者：
Li‐Jun Zhang;D. Knaust;Zhaoxia Zhao
中科院分区：
文献类型：
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作者：
Li‐Jun Zhang;D. Knaust;Zhaoxia Zhao
四川省甘西地区上泥盆统（弗拉斯期）土桥子组浅海沉积中，发现了大量的珊瑚遗迹化石。它由U形的火山灰洞穴组成，这些洞穴或多或少平行于或稍微倾斜于泥灰岩的层理。在根珊瑚洞穴中发现了四种类型的铁框架体（大部分是由黄铁矿框架体氧化而来），包括（1）光滑、有鞘的球形，（2）棱柱形，（3）八面体和（4）五角体亚微米晶体。化学上，亚微米晶体主要由铁、硫、氧和碳组成。铁框架状体代表了由于硫酸盐还原菌的活动，其原始黄铁矿框架状体从不规则形态和球形框架状体到八面体和五角体习性的演化阶段。在珊瑚外没有观察到类似的framboids。因此，这是可能的硫酸盐还原菌殖民theRocalliumspreite和边缘管内的dysopolysis环境。随着孔隙水氧化程度的增加，黄铁矿类铁闪石被部分氧化成铁类铁闪石，并在特殊情况下保留了晶体的原始形态。此外，提出了研究的珊瑚是由其跟踪标记的园艺与多功能的目的，其中不同的微生物菌落种植和培养的边缘管和spreite在食物供应和氧化还原条件的相互基础上。这些特征表明，沉积-摄食-园艺相结合的模式可能适用于赣西泥盆系的珊瑚礁群落的构建。负责的痕迹制造者可能是一种蠕虫状的有机体，比如多毛类动物。
The trace fossilRhizocorallium communeis abundant in shallow-marine deposits of the Upper Devonian (Frasnian) Tuqiaozi Formation in Ganxi, Sichuan Province, South China. It consists of U-shaped spreite burrows developed more or less parallel or slightly inclined to the bedding of marly limestone. Four types of iron framboids (mostly oxygenated from pyrite framboids) were found within theRhizocoralliumburrow, including (1) smooth, sheathed spherical, (2) prismatic, (3) octahedral, and (4) pyritohedral submicron crystals. Chemically, the submicron crystals mainly consist of iron, sulphur, oxygen and carbon. The iron framboids represent the stage of evolution of their original pyrite framboids from irregular morphologies and spherical framboids to octahedral and pyritohedral habits due to the activity of sulphate-reducing bacteria. No similar framboids were observed outsideRhizocorallium. Therefore, it is likely that sulphate-reducing bacteria colonised theRhizocoralliumspreite and marginal tube within a dysoxic environment. With increasing degree of oxygenation of pore water, the pyrite framboids were partly oxygenated into iron framboids and by exceptional circumstances preserved the original morphology of the crystals. Furthermore, it is proposed that the investigatedRhizocoralliumwas constructed by its trace maker for gardening with multifunctional purpose, where different microbial colonies were planted and cultured in the marginal tube and spreite on the mutual basis of food supply and redox conditions. These features indicate that a combined deposit-feeding and gardening model may apply for the construction ofRhizocorallium communefrom the Devonian of Ganxi. The responsible trace maker probably was a worm-like organism, such as a polychaete.