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Gunflint chert
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<h2 id="stratigraphy">Stratigraphy</h2> <p>The Gunflint Iron Formation is a <a href="/facts/Banded_iron_formation/b1eA2yAk">banded iron formation</a>, composed predominantly of dense <a href="/facts/Chert/pmvbVy6U">chert</a> and <a href="/facts/Slate/hSVHL6Lj">slate</a> layers interbedded with <a href="/facts/Ankerite/b09ywJzF">ankerite</a> <a href="/facts/Carbonate/FES1QHkN">carbonate</a> layers. The chert layers can be subdivided into black layers (containing organic material and <a href="/facts/Pyrite/41CYREyr">pyrite</a>), red layers (containing <a href="/facts/Hematite/716YBzGr">hematite</a>), and green layers (containing <a href="/facts/Siderite/2Vzd8MDE">siderite</a>).<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The Gunflint Iron Formation belongs to the <a href="/facts/Animikie_Group/3Y6sISfY">Animike Group</a> and can be broken up into four <a href="/facts/Stratigraphic_section/BBxnkItj">stratigraphic sections</a>, the Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty sections.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> <a href="/facts/Microfossil/PfE0lu1n">Microfossils</a> can be found in the <a href="/facts/Stromatolite/Wr208p5m">stromatolitic</a> chert layers, consisting of <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a>, algal filaments, spore-like spheroids, and organic-rich <a href="/facts/Ooid/lLK4Yf6t">ooids</a>. </p> <h2 id="history">History</h2> <p>Geologist Stanley A. Tyler first examined the <a href="/facts/Gunflint_Range/SSvNJaXy">Gunflint Range</a> in 1953 and observed red iron banded formations and black chert, noting probable <a href="/facts/Stromatolite/Wr208p5m">stromatolites</a>, though he would not go on to publish his observations for another decade. A. M. Goodwin later examined the geologic <a href="/facts/Facies/G73u7SIg">facies</a> of the Gunflint Iron Formation in 1956, resulting in one of the first science publications on the region,<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> but his report is devoid of any mention of microscopic life. The first publications noting the geobiological significance of the Gunflint Chert came in 1965 when two scientific papers highlighting the Gunflint <a href="/facts/Microfauna/C6whJqKQ">microfauna</a> were published in the preeminent journal <a href="/facts/Science_(journal)/uTyzjkwD"><i>Science</i></a>. These papers were Stanley Tyler and <a href="/facts/Elso_Sterrenberg_Barghoorn/yufdXvRh">Elso Barghoorn</a>'s ‘<a href="/facts/Microorganism/pysJYcE2">Microorganisms</a> from the Gunflint Chert’<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> and <a href="/facts/Preston_Cloud/gxPfmo1X">Preston Cloud</a>’s (University of California at Santa Barbara) ‘Significance of the Gunflint (<a href="/facts/Precambrian/zjF3N3Rx">Precambrian</a>) Microflora’.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> While published at nearly the same time, both papers served as landmark publications introducing the idea of life occurring during the Precambrian. Each paper had markedly different foci: while Barghoorn and Tyler aimed to characterize the individual microorganisms that comprise the Gunflint chert from a <a href="/facts/Taxonomy_(biology)/Qkg8wuyw">taxonomical</a> and <a href="/facts/Morphology_(biology)/Nl3B0myy">morphological</a> standpoint, Cloud focused on the larger-scale significance of the prospect of life existing during the Precambrian period and its implications for the field of Precambrian <a href="/facts/Paleontology/60n5yldd">paleontology</a>. The publication of these two seminal papers opened the floodgates to a vast array of paleontological and <a href="/facts/Geochemistry/05094gDu">geochemical</a> studies to explore Precambrian <a href="/facts/Microfossil/PfE0lu1n">microfossils</a> from similar Proterozoic environments. </p> <h2 id="age">Age</h2> <p>The Gunflint chert microfauna is mid- to late-<a href="/facts/Paleoproterozoic/gMS69p5r">Paleoproterozoic</a> in age (approximately 1.878 Ga ± 1.3 <a href="/facts/Myr/DXcnXuAw">Ma</a>, as determined by <a href="/facts/Uranium%25E2%2580%2593lead_dating/LMCJBhrQ">Uranium-Lead dating</a> techniques).<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> This age has fluctuated as dating techniques have become more accurate and precise. Initial whole-rock <a href="/facts/Rb-Sr_dating/F1NA2T58">Rubidium-Strontium</a> and <a href="/facts/K%25E2%2580%2593Ar_dating/JQdWfdIB">Potassium-Argon</a> dating placed the age of the Gunflint Iron Formation at 1.56-163 <a href="/facts/Bya/5E7foypY">Ga</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a><a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a><a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a><a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> Whole-rock <a href="/facts/Samarium%25E2%2580%2593neodymium_dating/TaRx8jYl">Neodymium-Samarium dating</a> later placed the age between 2.08 and 2.11 Ga.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> Finally, dating of interbedded <a href="/facts/Volcanic_ash/c3cqgBfV">ash</a> layers within the Gunflint Iron Formation yielded ages between 1.86 and 1.99 Ga,<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> which are most similar to the current consensus age of 1.878 Ga ± 1.3 Ma. At the time of discovery of the Gunflint Chert, the oldest evidence of life known was the <a href="/facts/Ediacaran_biota/1lx1CXxT">Ediacaran fauna</a> (635-541 Ma),<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> a late Precambrian assemblage less than half the age of the Gunflint microorganisms. </p> <h2 id="microfaunal-diversity">Microfaunal diversity</h2> <p>The most abundant organisms in Gunflint are <a href="/facts/Filamentous_bacteria/K9sFGTCu">filaments</a> found in <a href="/facts/Stromatolite/Wr208p5m">stromatolitic</a> fabrics, and typically range from 0.5-6.0 <a href="/facts/Micrometre/7eDFxD2L">μm</a> in diameter and up to several hundred <a href="/facts/Micrometre/7eDFxD2L">microns</a> in length.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> The Gunflint <a href="/facts/Microfauna/C6whJqKQ">microfauna</a> can be split into two broad categories: filaments and <a href="/facts/Spheroid/GJyyLxQ7">spheroids</a>. In the groundbreaking 1965 Barghoorn and Tyler paper, three new <a href="/facts/Genus/m8EFjSms">genera</a> and four new <a href="/facts/Species/oDg6b96r">species</a> of filamentous <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a> were discovered from Gunflint chert.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> Since then various new genera and species have been identified, some named after Barghoorn, Tyler, and Cloud in acknowledgement of their early contributions in defining the Gunflint <a href="/facts/Microorganism/pysJYcE2">microbial</a> <a href="/facts/Faunal_assemblage/jncSvd5X">assemblages</a>.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a><a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a><a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a><a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> </p> <h2 id="filamentous-microorganisms">Filamentous microorganisms</h2> <p><a href="/facts/Filamentation/K9sFGTCu">Filamentous</a> <a href="/facts/Microorganism/pysJYcE2">microorganisms</a> within the Gunflint <a href="/facts/Chert/pmvbVy6U">Chert</a> represent a mixed population of <a href="/facts/Photosynthesis/TMV7w693">photosynthetic</a> <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a> and <a href="/facts/Iron-oxidizing_bacteria/tUk32vjY">iron oxidizing bacteria</a>. On the <a href="/facts/Outcrop/3MC1NG4y">outcrop</a> scale, the filamentous Gunflint cyanobacteria form meter-scale <a href="/facts/Stromatolite/Wr208p5m">stromatolitic</a> domes, which are discernible along the Gunflint Iron Formation <a href="/facts/Stratigraphic_section/BBxnkItj">stratigraphic section</a>. Examples of newly identified filamentous genera and species within the Gunflint Chert include the genus <i><a href="/facts/Gunflintia/1as1zNHl">Gunflintia</a></i> and the species <i>Animikiea</i> <i>septate</i>, <i>Entosphaeroides amplus</i>, and <i>Archaeorestis schreiberensis</i>.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> </p> <h2 id="spheroidal-microorganisms">Spheroidal microorganisms</h2> <p><a href="/facts/Spheroid/GJyyLxQ7">Spheroidal</a> <a href="/facts/Spore/6qDRdcrs">spore</a>-like bodies within the Gunflint <a href="/facts/Chert/pmvbVy6U">Chert</a> are found irregularly distributed throughout the Gunflint Iron Formation, and range from 1 to 16 <a href="/facts/Micrometre/7eDFxD2L">μm</a> in diameter. The spheroidal bodies range from spherical to ellipsoidal in <a href="/facts/Morphology_(biology)/Nl3B0myy">morphology</a>. They are typically encased in a membrane which can vary in wall thickness and morphology. The spheroidal bodies have been hypothesized to be various things, such as <a href="/facts/Unicellular_organism/9PQsRuHU">unicellular</a> <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a>, <a href="/facts/Endogeny_(biology)/DFkSLkRI">endogenously</a> produced <a href="/facts/Endospore/UKWvt6Qu">endospores</a> of <a href="/facts/Bacteria/wC8xSCsU">bacterial</a> origin, free-swimming <a href="/facts/Dinoflagellate/jcQuSgM3">dinoflagellates</a>, and <a href="/facts/Fungus/BHo5DP59">fungus</a> <a href="/facts/Spore/6qDRdcrs">spores</a>.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> Examples of newly identified spheroidal genera and species within the Gunflint Chert include the genera <i>Huroniospora</i> and <i>Eoasatrion</i>, as well as the species <i>Eosphaera tyleri</i>.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a><a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> </p> <h2 id="preservation-of-microfauna">Preservation of microfauna</h2> <p>Various predominant <a href="/facts/Taphonomy/x4zxN2Hm">taphonomic</a> models have been suggested as mechanisms for the exceptional preservation of the Gunflint Chert <a href="/facts/Microfauna/C6whJqKQ">microfauna</a>. Examples of these taphonomic models include organic residue preservation, fine-grain <a href="/facts/Pyritization/IquXFKhR">pyritization</a>, coarse-grain pyritization, <a href="/facts/Carbonate/FES1QHkN">carbonate</a> association, and <a href="/facts/Hematite/716YBzGr">hematite</a> preservation.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> In organic residue preservation, a film of light-to-dark brown organic material outlines <a href="/facts/Microorganism/pysJYcE2">microorganisms</a>, acting as a stain and preserving filaments, spore-like bodies, and carbonate <a href="/facts/Rhombohedron/S7XSr6Yu">rhombs</a> within <a href="/facts/Chert/pmvbVy6U">chert</a>. Fine-grain pyritization is the most common type of preservation in the Gunflint Cherts, in which association of fine-grained (<a href="/facts/Micrometre/7eDFxD2L">micrometer</a> scale) <a href="/facts/Pyrite/41CYREyr">pyrite</a> with organic matter preserves the <a href="/facts/Morphology_(biology)/Nl3B0myy">morphology</a> of filamentous and spheroidal microorganisms.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> Coarse-grained pyritization occurs when millimeter scale pyrite minerals replace organic matter in cherts, preserving microorganism morphology. In carbonate association, filaments, spore-like bodies, and other organic structures can be preserved by carbonate mineralization (<1<a href="/facts/Micrometre/7eDFxD2L">μm</a> in diameter) imbedded in a chert <a href="/facts/Matrix_(geology)/dDgk5G1H">matrix</a>.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> Carbonate minerals can form as continuous bodies or as a series of lenses outlining filamentous cyanobacterial remains. Carbonate mineralization is often seen trailing pyrite crystals. Hematite preservation is a less common taphonomic mode, but is occasionally found at the interface between black <a href="/facts/Stromatolite/Wr208p5m">stromatolitic</a> cherts and red <a href="/facts/Jasper/smwAdKc0">jasper</a>. In this preservational method, hematite filaments <1μm in diameter encase (and occasionally replace) filamentous fossils, and are often outlined by carbonaceous films and pyrite grains.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a> As a result of the remarkable preservation of microorganisms given the taphonomic modes described above, the Gunflint Chert is sometimes described as the first Precambrian <a href="/facts/Lagerst%25C3%25A4tte/ByI7PT8h">lagerstätte</a>, or exceptionally preserved fossil assemblage.<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> </p> <h2 id="significance-and-paleoenvironmental-implications">Significance and paleoenvironmental implications</h2> <p>In the 1950s and 1960s, the state of the Precambrian atmosphere was not well characterized. The discovery of the Gunflint <a href="/facts/Microbiota/V4ymrawz">microbiota</a> revealed that <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a> (or an ancient <a href="/facts/Autotroph/UDc8bzqD">autotrophic</a> precursor modality) was occurring 1.8 billion years ago, and that the atmosphere was oxygenated enough to sustain microbial life.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> The mineralogy of the Gunflint banded iron formation reveals a complex relationship between these <a href="/facts/Redox/Pyd5RVcj">redox</a> conditions throughout the Gunflint Formation.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> Multiple iron species in the Gunflint formation provides evidence for a highly oxidative atmosphere, with some localized reducing conditions which allowed for the transport of large quantities of iron in a soluble ferrous state.<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> </p><p>While the Gunflint microfauna no longer represents the oldest life discovered on Earth, at the time of discovery it pushed back the presumptive age of photosynthesis and the origin of life boundary by over one billion years. This discovery spurred generations of <a href="/facts/Paleontology/60n5yldd">paleontologists</a> and <a href="/facts/Geomicrobiology/8SWXd403">geomicrobiologists</a> to contemplate ancient atmospheric oxygen conditions and redox states, and to continue searching for older microbial life. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Oxygen_catastrophe/LmTyM8jT">Oxygen catastrophe</a></li> <li><a href="/facts/Animikie_Group/3Y6sISfY">Animikie Group</a></li></ul> <ul><li>Schopf, J.W., 1999: <i>Cradle of Life: The Discovery of Earth's Earliest Fossils</i>. Princeton University Press, 336 p. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-691-00230-4</li> <li><a href="https://web.archive.org/web/20050413081040/http://geowords.com/histbooknetscape/k26.htm">Superior type Banded Iron Formation</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Fralick, P., David, D. W. and Kissin, Stephen A. (2002). "The age of the Gunflint Formation, Ontario, Canada: single zircon U–Pb age determinations". Canadian Journal of Earth Sciences. 39 (7): 1085–1091. doi:10.1139/E02-028.{{cite journal}}: CS1 maint: multiple names: authors list (link) <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Barghoorn, E. S. and Tyler, S. A., 1965: Microorganisms from the Gunflint Chert. Science, vol. 147, p. 563–577. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Awramik, Stanley M.; Barghoorn, Elso S. (August 1977). "The Gunflint microbiota". Precambrian Research. 5 (2): 121–142. Bibcode:1977PreR....5..121A. doi:10.1016/0301-9268(77)90025-0. ISSN 0301-9268. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Cloud, P. E. (1965-04-02). "Significance of the Gunflint (Precambrian) Microflora: Photosynthetic oxygen may have had important local effects before becoming a major atmospheric gas". Science. 148 (3666): 27–35. doi:10.1126/science.148.3666.27. ISSN 0036-8075. PMID 17773767. S2CID 37713079. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Goodwin, Alan Murray (1956-09-01). "Facies relations in the Gunflint iron formation [Ontario]". Economic Geology. 51 (6): 565–595. doi:10.2113/gsecongeo.51.6.565. ISSN 1554-0774. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Past lives: Chronicles of Canadian Paleontology "GSC :: Past lives: Chronicles of Canadian Paleontology - 5. Gunflint Chert". Archived from the original on 2005-06-12. Retrieved 2005-06-12. <a href="https://web.archive.org/web/20050612083155/http://gsc.nrcan.gc.ca/paleochron/05_e.php" target="_blank">https://web.archive.org/web/20050612083155/http://gsc.nrcan.gc.ca/paleochron/05_e.php</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Barghoorn, E. S. and Tyler, S. A., 1965: Microorganisms from the Gunflint Chert. Science, vol. 147, p. 563–577. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Goodwin, Alan Murray (1956-09-01). "Facies relations in the Gunflint iron formation [Ontario]". Economic Geology. 51 (6): 565–595. doi:10.2113/gsecongeo.51.6.565. ISSN 1554-0774. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Planavsky, Noah; Rouxel, Olivier; Bekker, Andrey; Shapiro, Russell; Fralick, Phil; Knudsen, Andrew (August 2009). "Iron-oxidizing microbial ecosystems thrived in late Paleoproterozoic redox-stratified oceans". Earth and Planetary Science Letters. 286 (1–2): 230–242. Bibcode:2009E&PSL.286..230P. doi:10.1016/j.epsl.2009.06.033. ISSN 0012-821X. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Goodwin, Alan Murray (1956-09-01). "Facies relations in the Gunflint iron formation [Ontario]". Economic Geology. 51 (6): 565–595. doi:10.2113/gsecongeo.51.6.565. ISSN 1554-0774. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Barghoorn, E. S. and Tyler, S. A., 1965: Microorganisms from the Gunflint Chert. Science, vol. 147, p. 563–577. <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Cloud, P. E. (1965-04-02). "Significance of the Gunflint (Precambrian) Microflora: Photosynthetic oxygen may have had important local effects before becoming a major atmospheric gas". Science. 148 (3666): 27–35. doi:10.1126/science.148.3666.27. ISSN 0036-8075. PMID 17773767. S2CID 37713079. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Fralick, P., David, D. W. and Kissin, Stephen A. (2002). "The age of the Gunflint Formation, Ontario, Canada: single zircon U–Pb age determinations". Canadian Journal of Earth Sciences. 39 (7): 1085–1091. doi:10.1139/E02-028.{{cite journal}}: CS1 maint: multiple names: authors list (link) <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Hurley, P. M.; Fairbairn, H. W.; Pinson, W. H.; Hower, J. (July 1962). "Unmetamorphosed Minerals in the Gunflint Formation Used to Test the Age of the Animikie". The Journal of Geology. 70 (4): 489–492. Bibcode:1962JG.....70..489H. doi:10.1086/626839. ISSN 0022-1376. S2CID 140697996. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>PETERMAN, ZELL E. (1966). "Rb-Sr Dating of Middle Precambrian Metasedimentary Rocks of Minnesota". Geological Society of America Bulletin. 77 (10): 1031. Bibcode:1966GSAB...77.1031P. doi:10.1130/0016-7606(1966)77[1031:rdompm]2.0.co;2. ISSN 0016-7606. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>FAURE, GUNTER; KOVACH, JACK (1969). "The Age of the Gunflint Iron Formation of the Animikie Series in Ontario, Canada". Geological Society of America Bulletin. 80 (9): 1725. 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