Microbial biomineralization processes forming modern Ca:Mg carbonate stromatolites
Microbial biomineralization processes forming modern Ca:Mg carbonate stromatolites
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DOI：
10.1111/j.1365-3091.2009.01083.x
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发表时间：
2010-01
期刊：
影响因子：
3.5
通讯作者：
A. Spadafora;E. Perri;J. Mckenzie;C. Vasconcelos
中科院分区：
文献类型：
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作者：
A. Spadafora;E. Perri;J. Mckenzie;C. Vasconcelos
现代钙镁碳酸盐叠层石的形式与微生物垫在高盐度的沿海泻湖，拉戈阿韦尔梅利亚（巴西）。尽管基质层表现出以薄或粗糙的层压和/或血栓性凝血为特征的多样化的结构，但其表现出普遍的Peloidal微结构。球粒状结构由极高镁方解石和/或钙白云石的暗色微晶聚集体组成，这些聚集体由亚微米三角多面体和有机质的等向组合形成。这些聚集体周围是排列在球晶中的透明的文石针状晶体。与文石晶体不同的是，有机物质始终存在于黑暗中，泥晶碳酸盐组成的泥质。这种有机物被观察为高镁方解石和钙白云石晶体间隙内的亚微米扁平和丝状粘液样结构，并被解释为降解的细胞外聚合物的残留物。此外，许多细菌细胞与碳酸盐相严格相关。这些细胞主要由直径为0.2至4 μm的亚球形、杆状和丝状形式组成，呈孤立或集落样簇。化石细胞外聚合物和细菌体的共存，与Ca：Mg碳酸盐多面体相关，意味着有机质和微生物代谢在形成泥质的矿物沉淀中发挥了重要作用。相比之下，文石相中缺乏胞外聚合物表明了另外的沉淀机制。在现代拉戈阿韦尔梅利亚微生物垫中诱导矿物沉淀的复杂过程似乎记录在所研究的石化基质中。高镁方解石和/或钙白云石的亚微米多面体晶体的形成是由于碳酸盐纳米颗粒在降解有机物核周围的聚结。亚微米多面体晶体聚集形成更大的卵形晶体，构成丸状体。随后在球粒周围的文石球晶的沉淀随着球粒周围的微环境水条件的变化而发生。
Modern Ca:Mg carbonate stromatolites form in association with the microbial mat in the hypersaline coastal lagoon, Lagoa Vermelha (Brazil). The stromatolites, although showing diversified fabrics characterized by thin or crude lamination and/or thrombolitic clotting, exhibit a pervasive peloidal microfabric. The peloidal texture consists of dark, micritic aggregates of very high‐Mg calcite and/or Ca dolomite formed by an iso‐oriented assemblage of sub‐micron trigonal polyhedrons and organic matter. Limpid acicular crystals of aragonite arranged in spherulites surround these aggregates. Unlike the aragonite crystals, organic matter is present consistently in the dark, micritic carbonate comprising the peloids. This organic matter is observed as sub‐micron flat and filamentous mucus‐like structures inside the interspaces of the high‐Mg calcite and Ca dolomite crystals and is interpreted as the remains of degraded extracellular polymeric substances. Moreover, many fossilized bacterial cells are associated strictly with both carbonate phases. These cells consist mainly of 0·2 to 4 μm in diameter, sub‐spherical, rod‐like and filamentous forms, isolated or in colony‐like clusters. The co‐existence of fossil extracellular polymeric substances and bacterial bodies, associated with the polyhedrons of Ca:Mg carbonate, implies that the organic matter and microbial metabolism played a fundamental role in the precipitation of the minerals that form the peloids. By contrast, the lack of extracellular polymeric substances in the aragonitic phase indicates an additional precipitation mechanism. The complex processes that induce mineral precipitation in the modern Lagoa Vermelha microbial mat appear to be recorded in the studied lithified stromatolites. Sub‐micron polyhedral crystal formation of high‐Mg calcite and/or Ca dolomite results from the coalescence of carbonate nanoglobules around degraded organic matter nuclei. Sub‐micron polyhedral crystals aggregate to form larger ovoidal crystals that constitute peloids. Subsequent precipitation of aragonitic spherulites around peloids occurs as micro‐environmental water conditions around the peloids change.