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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

3.2-G澳大利亚皮尔巴拉海岸克里弗维尔群的狄克逊岛组是保存中太古代海洋地层的最佳层序之一，可能含有微生物物质。野外观察和地球化学证据表明，狄克逊岛组中存在太古代海洋低温热液喷口系统和生物微生物群落。狄克逊岛组厚度约为350 m，由流纹岩凝灰岩、黑燧石和杂色燧石组成。流纹岩凝灰岩段中大量的黑色硅质岩脉群，表明黑硅质岩段沉积时有强烈的低温热液活动，厚15 ~ 20 m。文石、重晶石和石膏之后的丰富二氧化硅假像，以及明显连续的叠层石样生物垫层（厚10 - 20 cm），保存在层状黑燧石层中。叠层石状生物垫床形成了细铁或铱 ...更多信息在细粒二氧化硅内的涂层上的石英豌豆。黑硅质岩段中没有陆相碎屑沉积物和大量的脉状注入物，表明该沉积相在古深度约500 ~ 2000 m处为远洋热液环境，而不是很深的大洋面，如未成熟岛弧环境的斜坡。暗绿色硅质页岩和凝灰质层状燧石。这些岩石主要由非常细的石英组成。块状黑色燧石具有与黑色燧石脉相似的碳质球粒（直径0.3 mm-2 mm）。巨大的黑色燧石中含有螺旋形、棒状和树枝状的细菌物质。黑硅质岩和黑硅质岩脉的总有机碳（TOC）变化范围为0.05 ~ 0.16%（平均0.1%），碳同位素（δ ~（13）C）值为-32 ‰ ~ 27 ‰（平均30 ‰）。这一证据表明，黑硅质岩中的碳质颗粒和细菌状物质是生物成因的，形成于低温热液喷口系统附近。与热液活动有关的硅化作用可能使微生物菌落迅速石化。少