The Role of Cyanobacteria In the Microfabric Heterogeneity of Cambrian Leiolite, North China

IF 2 4区 地球科学 Q1 GEOLOGY
Ming-xiang Mei, M. Riaz, A. Koeshidayatullah, Ziliang Liu, M. Ahmed, Douaa Fathy
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Abstract

Based on their mesostructures, carbonate microbialites are divided into four major groups: laminated stromatolite, clotted thrombolites, structureless leiolites, and dendritic dendrolite. Among the various types of microbialites, leiolites, also known as “cryptomicrobial deposits,” are uncommon in the stratigraphic records. This is exacerbated by leiolites relatively structureless and aphanitic structure, making their identification and characterization more challenging. Previous studies have revealed that leiolites have contrasting fabrics at different scale, heterogeneous microscopic fabrics and structureless mesoscopic to macroscopic fabrics. While it is widely assumed that cyanobacteria play a significant role in the formation of carbonate microbialites in marine environments, the origin and controlling mechanisms of variations in leiolites microstructures and macrostructures remain enigmatic. In the central part of the North China Platform, two excellent exposures of massive, structureless Cambrian bioherms (Furongian) dominated by leiolites were observed (Qijayu section). The Qijayu-section leiolites offer a unique opportunity to investigate the role of cyanobacterial input in governing the formation and textural heterogeneities of such microbialites. In addition, the significance of the Furongian leiolites stems from their association with a period of global development of microbial-dominated carbonate platforms. Our findings suggest that these Furongian leiolites developed during the forced-regressive systems tract. At the microscopic level, these Furongian leiolites exhibit a high degree of heterogeneity which is controlled by the presence of various types of cyanobacteria (Hedstroemia, Subtifioria, Girvanella), sponge mummy, and benthic ooids. The Hedstroemia, Subtifioria and Girvanella excreted extracellular polymeric substances that form multiple biofilms in cyanobacterial microbial mats where Furongian leiolites grew. The role of cyanobacteria in the microscale heterogeneity of Cambrian leiolites is evident, and this provides new insights into the development of microbial-dominated carbonate platforms in similar settings elsewhere. As a result, this study provides not only a reference example for global correlation but also some solid clues for further understanding the growth style of leiolites in the geologic record.
蓝藻在华北寒武系亮纹岩微结构非均质性中的作用
碳酸盐微生物岩根据其细观结构可分为四大类:层状叠层石、凝块岩、无结构平面岩和枝状树突石。在各种类型的微生物岩中,平纹岩,也被称为“隐微生物矿床”,在地层记录中并不常见。平面岩相对无结构和隐晶结构加剧了这一点,使其识别和表征更具挑战性。以往的研究表明,平面岩具有不同尺度的结构差异,微观结构不均匀,介观-宏观结构无结构。虽然人们普遍认为蓝藻在海洋环境中碳酸盐微生物岩的形成中起着重要作用,但其微观结构和宏观结构变化的起源和控制机制仍然是一个谜。在华北地台中部(栖栖峪剖面),发现了2处以平纹岩为主的块状、无构造的寒武系芙蓉系生物礁。齐家峪剖面的平纹岩提供了一个独特的机会来研究蓝藻输入在控制这些微生物岩的形成和结构非均质性中的作用。此外,芙蓉系平滑岩的意义还在于它们与全球范围内以微生物为主的碳酸盐岩台地发育时期有关。我们的研究结果表明,这些芙蓉系的理纹岩是在强迫退退体系域发育的。在微观水平上,这些富龙纪的橄榄岩表现出高度的异质性,这是由各种蓝藻(Hedstroemia, Subtifioria, Girvanella),海绵木乃伊和底栖生物的存在所控制的。Hedstroemia、Subtifioria和Girvanella分泌胞外聚合物质,在富隆系橄榄岩生长的蓝藻微生物垫中形成多种生物膜。蓝藻在寒武系平面岩微尺度非均质性中的作用是明显的,这为其他类似环境下微生物主导的碳酸盐台地的发育提供了新的认识。该研究不仅为全球对比提供了参考范例,也为进一步认识地质记录中平面岩的生长方式提供了坚实的线索。
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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