SIMPLE STRUCTURES AND COMPLEX STORIES: POTENTIAL MICROBIALLY INDUCED SEDIMENTARY STRUCTURES IN THE EDIACARAN SERRA DE SANTA HELENA FORMATION, BAMBUÍ GROUP, EASTERN BRAZIL
SIMPLE STRUCTURES AND COMPLEX STORIES: POTENTIAL MICROBIALLY INDUCED SEDIMENTARY STRUCTURES IN THE EDIACARAN SERRA DE SANTA HELENA FORMATION, BAMBUÍ GROUP, EASTERN BRAZIL
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DOI：
10.2110/palo.2022.020
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发表时间：
2023-04
期刊：
影响因子：
1.6
通讯作者：
J. Okubo;L. Inglez;G. Uhlein;L. Warren;S. Xiao
中科院分区：
文献类型：
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作者：
J. Okubo;L. Inglez;G. Uhlein;L. Warren;S. Xiao
摘要：埃迪卡拉纪和下寒武统地层中存在大量的微生物沉积构造。然而，MISS分布和相之间的关系还没有彻底探讨在埃迪卡拉-寒武纪在南美洲的继承。本研究记录了巴西东部班布伊群埃迪卡拉纪晚期Serra de圣海伦娜组中MISS和其他潜在生物构造的出现。该单元位于含Cloudina的塞特拉戈阿斯组之上，是一个混合碳酸盐-硅质岩序列，缺乏宏观体化石。潜在的微生物结构包括褶皱结构，如“象皮”和Kinneyia样纹理，以及脓疱结构和丰富的阳性epirelief盘状结构。另一个假定的生物源结构是一个毫米宽的蜿蜒的凹槽，类似于一个简单的移动轨迹的小型游动的底栖后生动物。微生物表面纹理（即，“象皮”和Kinneyia型褶皱）主要见于异岩性沉积物中，通常位于砂岩和粉砂岩/页岩之间的界面处。另一方面，光盘显示相独立的分布，观察到的杂岩以及碳酸盐和泥灰岩沉积。岩石学分析表明，这些盘具有复杂的成因，其中一些可能是成岩构造。因此，虽然相可能强烈地控制了在塞拉德圣海伦娜组MISS相关的结构和纹理的保存，其丰富性和多样性的潮滩沉积物表明广泛分布的matgrounds在这些浅海古环境。此外，我们还展示了对盘状结构等简单特征的详细描述和分类是埃迪卡拉-寒武纪过渡时期海洋生态系统古环境重建的重要任务，因为微生物结合的基质在沿海环境的动态中发挥着重要作用。
ABSTRACT: Microbially induced sedimentary structures (MISS) are abundant in Ediacaran and lower Cambrian successions. However, the relationship between MISS distribution and facies has not been thoroughly explored in Ediacaran–Cambrian successions in South America. This study documents the occurrence of MISS and other potential biogenic structures from the late Ediacaran Serra de Santa Helena Formation in the Bambuí Group of eastern Brazil. This unit overlies the Cloudina-bearing Sete Lagoas Formation and is a mixed carbonate-siliciclastic succession devoid of macroscopic body fossils. Potential microbial structures include wrinkled structures such as “elephant-skin” and Kinneyia-like textures, as well as pustular structures and abundant positive epirelief discoidal structures. Another putative biogenic structure is a mm-wide meandering groove resembling a simple locomotion trail of a small vagile benthic metazoan. Microbial surface textures (i.e., “elephant skin” and Kinneyia-type wrinkles) were mainly observed in heterolithic deposits, usually at the interface between sandstone and siltstone/shale. On the other hand, discs show a facies-independent distribution, observed in heterolithic as well as carbonate and marl deposits. Petrographic analyses of these discs suggest that they have complex origins and some of them may be diagenetic structures. Thus, while facies may have strongly controlled the preservation of MISS-related structures and textures in the Serra de Santa Helena Formation, their abundance and diversity in tidal flat deposits indicate the wide distribution of matgrounds in these shallow marine paleoenvironments. Also, we demonstrate how detailed description and classification of simple features, such as discoidal structures, is an important task for paleoenvironmental reconstruction of marine ecosystems at the Ediacaran–Cambrian transition when the microbially bounded substrates played important roles in the dynamics of coastal environments.