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Seafloor silicification and hardground development during deposition of 2.5 Ga banded iron formations

2015; Geological Society of America; Volume: 43; Issue: 3 Linguagem: Inglês

10.1130/g36363.1

1943-2682

Birger Rasmussen, Bryan Krapež, Janet R. Muhling,

Geomagnetism and Paleomagnetism Studies

Research Article| March 01, 2015 Seafloor silicification and hardground development during deposition of 2.5 Ga banded iron formations Birger Rasmussen; Birger Rasmussen * 1Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia *E-mail: B.Rasmussen@curtin.edu.au Search for other works by this author on: GSW Google Scholar Bryan Krapež; Bryan Krapež 1Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia Search for other works by this author on: GSW Google Scholar Janet R. Muhling Janet R. Muhling 1Department of Applied Geology, Curtin University, Kent Street, Bentley, WA 6102, Australia2Centre for Microscopy Characterisation and Analysis, University of Western Australia, Stirling Highway, Crawley, WA 6009, Australia Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (3): 235–238. https://doi.org/10.1130/G36363.1 Article history received: 16 Oct 2014 rev-recd: 02 Jan 2015 accepted: 02 Jan 2015 first online: 09 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 Birger Rasmussen, Bryan Krapež, Janet R. Muhling; Seafloor silicification and hardground development during deposition of 2.5 Ga banded iron formations. Geology 2015;; 43 (3): 235–238. doi: https://doi.org/10.1130/G36363.1 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 SocietyGeology Search Advanced Search Abstract Banded iron formations (BIFs) are important archives of the ancient oceans, atmosphere, and biosphere, but fundamental questions remain about their origin. It is widely assumed that BIFs were derived from layers of ferric oxyhydroxides and silica that precipitated directly from a water column that was enriched in dissolved iron and silica. The reported lack of current-generated structures and clastic particles beyond mud grade, and the perceived basin-scale extent of laminae, is regarded as evidence for uninterrupted pelagic settling with no sedimentary reworking. New sedimentological and petrographic results show that laminated cherts in the 2.5 Ga Dales Gorge Member of the Brockman Iron Formation, Western Australia, preserve textures indicative of in situ brecciation immediately below the seafloor and the deposition of intraformational sandstones composed of chert clasts in a chert matrix. Chert intraclasts have two sedimentary components: silt-sized microgranules and submicron-sized particles, indicating that the original sediment comprised iron-rich silicate muds that were cemented on or just below the seafloor by pore-filling silica. Silicified muds were episodically eroded by density currents, and the resulting detritus was transported as sand-sized clasts and locally deposited in a matrix of microgranules and mud. Our results support the hypothesis that high concentrations of silica in early Precambrian seawater favored episodic silica cementation of sediments on the seafloor. We suggest that competition between sediment accumulation and seafloor silica cementation, with subsequent differential compaction, explains primary layering in BIFs between beds of relatively thickly laminated chert and beds of thinly laminated, iron-rich minerals. The thickest laminated chert beds are interpreted to represent intervals when seafloor silicification outpaced deposition of hydrothermal muds, forming the equivalent of Phanerozoic hardgrounds at sequence boundaries. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.