Restore the Archean oceanic hydrothemai cross section: Geologicai and geochemical approach for frnding of early biosphere

恢复太古宙海洋水热剖面：早期生物圈的地质和地球化学方法

基本信息

批准号：
14340153
负责人：
KIYOKAWA Shoichi
金额：
$ 9.41万
依托单位：
Kyishu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

The 3.2-Ga. Dixon Island Formation in the Cleaverville Group of the coastal Pilbara terrane, Australia, is one of the best sequences that preserves an example of middle Archean oceanic stratigraphy and contains possible microbial material. Field observations and geochemical evidence suggest that the Dixon Island Formation contains low temperature hydrothermal vents system with a biogenic microbial colony in the Archean ocean. The Dixon Island Formation is approximately 350 m thick and consists of the Rhyolite Tuff, Black Chert and Varicolored Chert members. Many black-chert vein swarms in the Rhyolite Tuff Member imply intensive low-temperature hydrothermal activity during deposition of the Black Chert Member, which is 15〜20 m thick. Abundant pseudomorph of silica after aragonite, barite, and gypsum, and a distinctly continuous, stromatolite-like biomat layer (10〜20 cm in thick), are preserved within the laminated black-chert bed. The stromatolite-like biomat bed formed fine iron or ir … More on-coated quartz pisoids within fine-grained silica. The absence of detrital sediments of continental origin and many vein injection implies that this sedimentary facies represents a pelagic hydrothermal environment at about 500〜2000 m in paleodepth, which is not very deep oceanic plane, such as a slope of immature island arc setting.Microbial material has been preserved well in the Black Chert Member, which is composed of massive black chert, laminated black chert, dark greenish siliceous shale and tuffaceous laminated chert. These rocks are mainly composed very fine quartz. The massive black chert has carbonaceous peloids (0.3 mm〜2 mm in diameter) similar to those in the black chert veins. The massive black chert contains spiral-, rod- and dendrite-shaped bacterial material. Total organic carbon (TOC in the black chert and black chert veins varies within 0.05〜0.16% (average 0.1%) and the carbon isotope (delta 13C values of these rocks are -32〜-27 per mil (average 30 per mill). This evidence suggests that the carbonaceous grains and bacteria-shaped material in the black cherts are biogenic origin and formed close to a low temperature hydrothermal vent system. The microbial colony might have been quickly fossilized by silicification related to hydrothermal activity. Less

澳大利亚沿海皮尔巴拉地体 Cleaverville 群的 3.2 Ga. Dixon 岛地层是保存太古宙中期海洋地层实例的最佳序列之一，并且包含可能的微生物物质。岛层包含太古代海洋中的低温热液喷口系统和生物微生物菌落。迪克森岛层厚约 350 m，由流纹岩组成。凝灰岩、黑燧石和杂色燧石岩段。流纹岩凝灰岩段中存在许多黑燧石脉群，表明黑燧石岩段沉积期间存在强烈的低温热液活动，其厚度为 15-20 m，继文石之后存在丰富的二氧化硅假晶。重晶石、石膏以及明显连续的叠层石状生物垫层（厚 10-20 厘米）保存在层压板内类似叠层石的生物垫床在细粒二氧化硅内形成了细铁或红外沉积物，缺乏大陆起源的碎屑沉积物和许多静脉注入意味着该沉积相代表了远洋热液。古深度500~2000 m左右的环境，不是很深的洋面，如未成熟岛弧的斜坡黑燧石段微生物物质保存较好，由块状黑色燧石、层状黑色燧石、深绿色硅质页岩和凝灰质层状燧石组成，这些岩石主要由细小的石英组成。与黑燧石矿脉相似的球体（直径 0.3 毫米至 2 毫米），块状黑燧石含有螺旋状、棒状和树枝状细菌物质。总有机碳（黑燧石和黑燧石脉中的 TOC 变化范围为 0.05〜0.16%（平均 0.1%），碳同位素（这些岩石的 δ 13C 值为 -32〜 -27 每密耳（平均每密耳 30 个）这一证据表明，黑燧石中的碳质颗粒和细菌状物质是生物来源的。微生物群落可能是在低温热液喷口系统附近形成的，可能是由于与热液活动有关的硅化作用而迅速化石化的。