Middle Archean volcano-hydrothermal sequence: Bacterial microfossil-bearing 3.2 Ga Dixon Island Formation, coastal Pilbara terrane, Australia

Abstract

Research Article| January 01, 2006 Middle Archean volcano-hydrothermal sequence: Bacterial microfossil-bearing 3.2 Ga Dixon Island Formation, coastal Pilbara terrane, Australia Shoichi Kiyokawa; Shoichi Kiyokawa 1Department of Earth and Planetary Science, Kyushu University, 6-10-1 Hakozaki Higashiku, Fukuoka, Japan Search for other works by this author on: GSW Google Scholar Takashi Ito; Takashi Ito 2Faculty of Education, Ibaraki University, 2-1-1 Bunkyo Mito-city, Ibaraki, Japan Search for other works by this author on: GSW Google Scholar Minoru Ikehara; Minoru Ikehara 3Marine Core Research Center, Kochi University, 2-5-1 Akebono-cho, Kochi-city, Japan Search for other works by this author on: GSW Google Scholar Fumio Kitajima Fumio Kitajima 4Department of Earth and Planetary Science, Kyushu University, 6-10-1 Hakozaki Higashiku, Fukuoka, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information Shoichi Kiyokawa 1Department of Earth and Planetary Science, Kyushu University, 6-10-1 Hakozaki Higashiku, Fukuoka, Japan Takashi Ito 2Faculty of Education, Ibaraki University, 2-1-1 Bunkyo Mito-city, Ibaraki, Japan Minoru Ikehara 3Marine Core Research Center, Kochi University, 2-5-1 Akebono-cho, Kochi-city, Japan Fumio Kitajima 4Department of Earth and Planetary Science, Kyushu University, 6-10-1 Hakozaki Higashiku, Fukuoka, Japan Publisher: Geological Society of America Received: 26 Oct 2004 Revision Received: 18 May 2005 Accepted: 31 May 2005 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2006) 118 (1-2): 3–22. https://doi.org/10.1130/B25748.1 Article history Received: 26 Oct 2004 Revision Received: 18 May 2005 Accepted: 31 May 2005 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Shoichi Kiyokawa, Takashi Ito, Minoru Ikehara, Fumio Kitajima; Middle Archean volcano-hydrothermal sequence: Bacterial microfossil-bearing 3.2 Ga Dixon Island Formation, coastal Pilbara terrane, Australia. GSA Bulletin 2006;; 118 (1-2): 3–22. doi: https://doi.org/10.1130/B25748.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The 3.2 Ga Dixon Island Formation in the Cleaverville Group of the coastal Pilbara terrane, Australia, is one of the most complete and best-preserved examples of middle Archean oceanic stratigraphy and contains possible microbial material. Field observations and geochemical evidence suggest that this formation contains a low-temperature hydrothermal vent system with a biogenic microbial colony from the Archean ocean. The Dixon Island Formation is ∼350 m thick and consists of the Rhyolite Tuff, Black Chert, and Varicolored Chert Members, in ascending order. The Rhyolite Tuff Member contains many vein swarms, such as quartz and black chert veins, and highly altered rhyolite tuff layers, which are identified as an underground bypass zone for circulating hydrothermal fluid. 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 10–15 m thick. The Black Chert Member is composed of massive black chert, laminated black chert, dark-greenish siliceous shale and tuffaceous laminated chert, which are mainly composed of very fine quartz. Abundant pseudomorphs of silica after aragonite, barite, and gypsum, and a distinctly continuous, stromatolite-like biomat layer (10–20 cm thick), are preserved within the laminated black chert bed. The stromatolite-like biomat bed is formed of fine iron or iron-coated quartz pisolite within fine-grained silica. The absence of detrital sediment of continental origin and the many vein injections imply that this sedimentary facies represents a pelagic hydrothermal environment at ∼500–2000 m paleodepth, and may have been on the slope of an immature island arc.Microbial material has been preserved well in the lower part of Black Chert Member. The massive black chert has carbonaceous peloids (0.3–2.0 mm in diameter), which are similar to those in the black chert veins. The massive black chert contains spiral-, rod, and dendrite-shaped bacterial material. The total organic carbon (TOC) value of massive black chert in the lower part of the Black Chert Member is higher (TOC = 0.15–0.45%) than that of the overlying laminated chert section (TOC = 0.02–0.15%) and the black chert vein (TOC = 0.1–0.13%), and the carbon isotope (δ13C) values of this lithology (−33‰ to ∼−27‰) are also lighter than for the black chert veins (−29‰ to ∼−26‰) and the laminated black chert in the upper part of the Black Chert Member and the Varicolored Chert Member (−27‰ to ∼−13‰). This evidence suggests that the carbonaceous grains and bacteria-shaped material in the lower part of the Black Chert Member are of bio-genic origin and were formed close to a low-temperature hydrothermal vent system. The microbial colony may have been rapidly fossilized by silicification related to hydrothermal activity. Laminated black chert in the upper part of the Black Chert and the Varicolored Chert Members may have formed by cyanobacterial sedimentation from the ocean surface. 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