Geobiology of a palaeoecosystem with Ediacara-type fossils: The Shibantan Member (Dengying Formation, South China)
Geobiology of a palaeoecosystem with Ediacara-type fossils: The Shibantan Member (Dengying Formation, South China)
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DOI：
10.1016/j.precamres.2014.09.012
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发表时间：
2014-12-01
影响因子：
3.8
通讯作者：
Reitner, Joachim
中科院分区：
文献类型：
--
作者：
Duda, Jan-Peter;Blumenberg, Martin;Reitner, Joachim
尽管埃迪卡拉型化石的古生态系统对后生动物的早期进化具有重要意义，但人们对这些环境中地质和生物过程的相互作用知之甚少。其原因是由于火山和硅屑岩性为主，沉积构造、生物构造和（生物）地球化学特征（如烃生物标志物）通常保存不完整。石板滩段（灯影组）是世界上为数不多的具有埃迪卡拉型生物的碳酸盐岩地层之一，其岩性保证了沉积作用和（生物）地球化学特征的良好保存。本文首次对十板滩段进行了全面的地球生物学表征，以重建沉积过程和（生物）地球化学过程之间的相互作用，并利用埃迪卡拉型化石评价古生态系统中的微生物活动。分析表明，碳酸盐岩和有机质是由与微生物席相关的（生物）地球化学过程自发形成的。然而，这些材料经常在同一环境（即准原生环境）中被重新加工和重新沉积，这可以通过小规模（丘状）交叉分层、侵蚀接触、透镜状层理和负荷铸造来证明。负Ce异常（Ce/Ce*）和低V/Cr比值表明水柱中存在分子O-2，而特征Ni/Co-， V/(V + Ni)和V/Sc比值表明同期存在亚氧至缺氧水。综上所述，这些观测结果暗示了一个暂时分层的水体，经常被风暴混合和通风。石版滩碳酸盐岩中C-13的富集（δ C-13 = +3.29 ~ + 3.98 ppm， VPDB），以及催化加氢热解从萃取残渣中裂解的同生正构烷烃中C-13的消耗（HyPy; δ C-13 = -31.7 ~ -363 ppm， VPDB），可能表明垫子内繁盛的初级生产者大量提取了C-12。同时，沥青和低热解产物中的硫化物生物标志物提示有机质分解和硫酸盐还原菌伴生硫化物。当沉积物和水的界面由于风暴的混合而产生氧气时，硫化物氧化细菌可能会暂时得到青睐。结果表明，古环境条件是通过生物成因和非生物成因过程的复杂相互作用而动态变化的。(C) 2014 Elsevier B.V.版权所有
Despite the importance of palaeoecosystems with Ediacara-type fossils for the early evolution of metazoans, only little is known about the interplay of geological and biological processes in these environments. The reason is that sedimentary structures, biogenic structures and (bio-) geochemical signatures (e.g. hydrocarbon biomarkers) are commonly not well preserved due to the predominance of volcanic and siliciclastic lithologies. The Shibantan Member (Dengying Formation, South China) is one of only few carbonate settings with Ediacara-type organisms worldwide and its lithology promises an excellent preservation of sedimentary fades and (bio-) geochemical signatures. Here we provide the first comprehensive geobiological characterisation of the Shibantan Member in order to reconstruct the interplay between sedimentary and (bio-) geochemical processes and to assess the microbial activities in the palaeoecosystem with Ediacara-type fossils. Fades analyses revealed that carbonate and organic matter were autochthonously formed by (bio-) geochemical processes linked to microbial mats. However, the material was frequently reworked and re-deposited within the same setting (i.e. para-autochthonous) as evidenced by small-scale (hummocky-) cross stratification, erosional contacts, lenticular bedding and load casts. Negative Ce anomalies (Ce/Ce*) and low V/Cr ratios demonstrate that molecular O-2 was present in the water column, whereas characteristic Ni/Co-, V/(V + Ni), and V/Sc ratios suggest the contemporaneous presence of sub- to anoxic water. Taken together, these observations imply a temporarily stratified water body frequently mixed and ventilated by storms. C-13-enrichments in the Shibantan carbonates (delta C-13 = +3.29 to + 3.98 parts per thousand, VPDB) together with C-13-depletions of syngenetic n-alkanes cleaved from the extraction residue using catalytic hydropyrolysis (HyPy; delta C-13 = -31.7 to -363 parts per thousand, VPDB) could indicate a significant withdrawal of C-12 by primary producers that thrived within the mats. At the same time, sulphurised biomarkers in the bitumen and HyPy-pyrolysate hint at organic matter decomposition and concomitant sulphide production by sulphate reducing bacteria. When oxygen was available at the sediment-water interface due to mixing by storms, sulphide oxidising bacteria were possibly temporarily favoured. The results demonstrated that palaeoenvironmental conditions dynamically changed through a complex interplay of biogenic and abiogenic processes. (C) 2014 Elsevier B.V. All rights reserved.