Evidence from laminated chert in banded iron formations for deposition by gravitational settling of iron-silicate muds

Abstract

Research Article| January 08, 2019 Evidence from laminated chert in banded iron formations for deposition by gravitational settling of iron-silicate muds Birger Rasmussen; Birger Rasmussen * 1School of Earth Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA3State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, Hubei, China *E-mail: birger.rasmussen@uwa.edu.au Search for other works by this author on: GSW Google Scholar Janet R. Muhling; Janet R. Muhling 1School of Earth Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia Search for other works by this author on: GSW Google Scholar Woodward W. Fischer Woodward W. Fischer 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Birger Rasmussen * 1School of Earth Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA3State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, Hubei, China Janet R. Muhling 1School of Earth Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia Woodward W. Fischer 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA *E-mail: birger.rasmussen@uwa.edu.au Publisher: Geological Society of America Received: 05 Sep 2018 Revision Received: 01 Dec 2018 Accepted: 09 Dec 2018 First Online: 08 Jan 2019 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2019 Geological Society of America Geology (2019) 47 (2): 167–170. https://doi.org/10.1130/G45560.1 Article history Received: 05 Sep 2018 Revision Received: 01 Dec 2018 Accepted: 09 Dec 2018 First Online: 08 Jan 2019 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, Janet R. Muhling, Woodward W. Fischer; Evidence from laminated chert in banded iron formations for deposition by gravitational settling of iron-silicate muds. Geology 2019;; 47 (2): 167–170. doi: https://doi.org/10.1130/G45560.1 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 The deposition of clay-sized particles by settling from suspension within a water column typically forms highly porous (80%–90% water) muds dominated by uniformly distributed and randomly oriented particles. The depositional microfabric of muds is rapidly destroyed during burial, resulting in mudstones with a strong preferred particle orientation. Here we show that laminated chert in banded iron formations from the Hamersley Group, Australia, and Ghaap Group, South Africa, preserve laminae of nanometer-sized particles of greenalite with textures that resemble the fabric of freshly deposited muds—the oldest such fabrics in the rock record. The preservation of the textures implies that the nanoparticles were “frozen” by silica cement on or just below the seafloor, an interpretation supported by their presence in intraformational chert clasts and nodules with strong differential compaction. The co-occurrence of stacks of plates forming thicker aggregates with multiple face-to-edge contacts indicates that the greenalite may have been deposited as loosely formed flocs. The common occurrence, in certain horizons, of iron-silicate microgranules dispersed in the greenalite mud resembles aggregates of clay particles documented in modern muds. These textures support models for active seawater precipitation of the iron-rich phases and point to collision and flocculation of particles during sediment transport. Upon deposition, amorphous silica rapidly occluded the available porosity and entombed the precipitates in a chemically inert cement that limited burial-related compaction and hindered diagenetic reactions, providing a taphonomic view of the earliest mineralogy and texture of iron formations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.