Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits

Research Article| April 01, 2003 Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits Tor Grenne; Tor Grenne 1Geological Survey of Norway, Leiv Eirikssons vei 39, N-7491 Trondheim, Norway Search for other works by this author on: GSW Google Scholar John F. Slack John F. Slack 2U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Tor Grenne 1Geological Survey of Norway, Leiv Eirikssons vei 39, N-7491 Trondheim, Norway John F. Slack 2U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192, USA Publisher: Geological Society of America Received: 28 Jun 2002 Revision Received: 03 Dec 2002 Accepted: 05 Dec 2002 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2003) 31 (4): 319–322. https://doi.org/10.1130/0091-7613(2003)031<0319:PAMSRS>2.0.CO;2 Article history Received: 28 Jun 2002 Revision Received: 03 Dec 2002 Accepted: 05 Dec 2002 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Tor Grenne, John F. Slack; Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits. Geology 2003;; 31 (4): 319–322. doi: https://doi.org/10.1130/0091-7613(2003)031<0319:PAMSRS>2.0.CO;2 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 Laterally extensive beds of highly siliceous, hematitic chert (jasper) are associated with many volcanogenic massive sulfide (VMS) deposits of Late Cambrian to Early Cretaceous age, yet are unknown in analogous younger (including modern) settings. Textural studies suggest that VMS-related jaspers in the Ordovician Løkken ophiolite of Norway were originally deposited as Si- and Fe-rich gels that precipitated from hydrothermal plumes as colloidal silica and iron-oxyhydroxide particles. Rare earth element patterns and Ge/Si ratios of the jaspers reflect precipitation from plumes having seawater dilution factors of 103 to 104, similar to modern examples. We propose that silica in the ancient jaspers is not derived from submarine hydrothermal fluids—as suggested by previous workers—but instead was deposited from silica-rich seawater. Flocculation and precipitation of the silica were triggered inorganically by the bridging effect of positively charged iron oxyhydroxides in the hydrothermal plume. A model involving amorphous silica (opal-A) precursors to the jaspers suggests that silica contents of Cambrian–Early Cretaceous oceans were at least 110 mg/L SiO2, compared to values of 40–60 mg/L SiO2 estimated in other studies. The evolution of ancient silica-rich to modern Fe-rich precipitates in submarine-hydrothermal plumes reflects a changeover from silica-saturated to silica-depleted seawater through Phanerozoic time, due mainly to ocean-wide emergence of diatoms in the Cretaceous. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.