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<title>SOES 3006: Earliest Microfossil evidence - Examples</title>
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<h1>Examples</h1>
<p>Below you will find detailed information on the 5 main microfossil groups described on the "Ages" page. This information is taken from relevant and recent research papers published in reputable journals or textbooks. Click on one of the links below to jump to a specific group, alternatively keep scrolling down to view them in age order (youngest to oldest). </p>
<p align="center"><a href="examples.html#bittersprings">Bitter Springs Chert</a></p>
<p align="center"><a href="examples.html#gunflint">Gunflint Chert</a></p>
<p align="center"><a href="examples.html#apex">Apex Chert</a></p>
<p align="center"><a href="examples.html#onverwacht">Onverwacht Group</a></p>
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<h2><a name="bittersprings" id="bittersprings"></a><a name="1976walter" id="1976walter"></a><a name="1982vanyo" id="1982vanyo"></a><a name="1985vanyo" id="1985vanyo"></a><a name="2000hill" id="2000hill"></a><a name="2005grey" id="2005grey"></a><a name="1968schopf" id="1968schopf"></a><a name="1971schopf" id="1971schopf"></a>Bitter Springs Chert </h2>
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<img src="Images/bitterspringsmap.JPG" alt="Fig 1. Location map of Bitter Springs Chert in Central Australia " width="146" height="119"><br />
<p>Fig 1. Location map of Bitter Springs Chert in Central Australia </p>
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<p>The Bitter Springs formation was originally given an age of 900 to 750 Ma by <a href="moreinfo.html#walter1976">Walter <em>et al.</em> (1976)</a>. This date has since been revised many times [eg., <a href="moreinfo.html#vanyo1982">Vanyo and Awramik, (1982)</a>, <a href="moreinfo.html#vanyo1985">Vanyo and Awramik, (1985)</a> and <a href="moreinfo.html#hill2000">Hill & Walter, (2000)</a>] with the latest estimate being ~802 Ma [<a href="moreinfo.html#grey2005">Grey <em>et al</em>, (2005)</a>] giving it a Neoproterozoic age. The formation is best exposed 40 miles North East of Alice Springs in the Ross River area of the Amadeus Basin in Central Australia and is seen as a ~900m thick sequence of laminated black cherty limestones and dolomites interbedded with thin dark shales [<a href="moreinfo.html#schopf1968">Schopf, (1968)</a>].</p>
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<div align="center"><img src="Images/bittersprings2.JPG" alt="Fig 2. Example of a filamentous microfossil from the Bitter Springs Chert " width="284" height="224"></div>
<p>Fig 2. Example of a filamentous microfossil [<a href="moreinfo.html#schopf1968">Schopf, (1968)</a>] . </p>
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<p>The microfossils are found most commonly in laminated, chalcedonic lenses which may be iron stained or covered by a thin veneer of gypsum and are often brecciated and weathered [<a href="moreinfo.html#schopf1968">Schopf, (1968)</a>]. In thin section the fossiliferous cherts are yellowish-brown through to reddish-brown, typically 4 to 50 μm in thickness and are thought to be indicative of a shallow marine shelf environment [<a href="moreinfo.html#schopf1971">Schopf, (1971)</a>]. This environment is considered ideal for promoting the growth of microbiological communities. Organic preservation occurs in a similar way to that of modern stromatolites with successive undulatory organic layers being separated by thin inorganic layers. These mats are composed of filamentous structures (Fig. 2) which are interpreted as blue-green (cyanobacteria) algae which are enmeshed into an amorphous organic substrate which is thought to have encased and infilled the cells rapidly before crystallisation of the cherts protected them from geological trauma[<a href="moreinfo.html#schopf1971">Schopf, (1971)</a>]. In addition to these filamental structures, spheroidal morphotypes have been recognised with some possibly representing different stages of cell division which may possibly reveal some of the first signs of mitosis. In total over 50 taxa have been described from the Bitter Springs Chert and this number is likely to only be a tiny percentage of the natural abundance at the time. It is reasonable to assume that this particular era is likely to have been the time when these cyanobacteria were the most dominant organisms on the planet as mobile heterotrophic eukaryotes and grazing metazoans had not yet gained a foothold in the ecosystem. </p>
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<h2><a name="gunflint" id="gunflint"></a><a name="2002fralick" id="2002fralick"></a><a name="1965barghoorn" id="1965barghoorn"></a><a name="2000westall" id="2000westall"></a><a name="2002konhauser" id="2002konhauser"></a><a name="2000christensen" id="2000christensen"></a>Gunflint Chert </h2>
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<img src="Images/gunflintmap.JPG" alt="Fig 3. Location map of Gunflint Chert in Canada" width="146" height="160"><br>
<p>Fig 3. Location map of Gunflint Chert in Canada </p>
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<p>The Gunflint Chert is found in the middle of the Animikie Group of Northwestern Ontario, Canada (Fig. 3) and is dated at ~2 Ga by most papers however recent zircon dating by <a href="moreinfo.html#fralick2002">Fralick <em>et al.</em> (2002)</a> has yeilded an age of 1.878 Ma ± 1.3 Myr. The formation is characterised by jaspiric banded iron formation-type (BIF) deposits where layers of silica and hematite alternate with red (jasper), yellow and grey chert (Fig. 4).</p>
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<div align="center"><img src="Images/gunflint.jpg" alt="Fig 2. Example of a filamentous microfossil from the Bitter Springs Chert " width="272" height="348"></div>
<p>Fig 4. Jaspiric stromatolites in the Gunflint chert [Photo: GSC].</p>
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<p>The organisms preserved in the Gunflint Formation are most common found in the more siliceous regions in the lower 45m of the formation and typically show 3D preservation of filamentous and coccoidal morphotypes (Fig. 5) with length ranging from 50 to 200μm and a diameter range of 1 to 3μm [<a href="moreinfo.html#barghoorn1965">Barghoorn and Tyler, (1965)</a>]. These size ranges are within the common range of modern microbial filaments and also fit the size ranges of those seen in other localities. These microfossils are show iron-mineralised cell walls with occasional fossilised polymeric substances (FPS) [<a href="moreinfo.html#westall2000">Westall <em>et al.,</em> (2000)</a>]. The presence of such iron-precipitating microbes means that it may be possible that they were a mechanism in the formation of the BIF's [<a href="moreinfo.html#konhauser2002">Konhauser et al., (2002)</a>] or may not have precipitated iron and existed passively and played no part in BIF genesis.</p>
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<div align="left"><img src="Images/gunflint1.jpg" alt="Fig 5. SEM image of coccoidal fossils" width="146" height="119"><br>
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<p>Fig 5. SEM image of coccoidal fossils [<a href="moreinfo.html#barghoorn1965">Barghoorn and Tyler, (1965)</a>]</p>
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<p>Whilst the biogenicity of these putative microfossils is not certain, no alternate theory regarding these putative microfossils has been put forward and as such biogenicity remains the only possibility. The significance of these microfossils lies predominantly within the recently discovered BIF's on Mars [<a href="moreinfo.html#christensen2000">Christensen et al., (2000)</a>] and the possibility that iron-mineralisation of organism may also have existed extra-terrestrially in a similar way to that seen in the Gunflint Chert. </p>
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<h2><a name="apex" id="apex"></a><a name="1993schopf" id="1993schopf"></a><a name="2004schopf" id="2004schopf"></a><a name="1999schopf" id="1999schopf"></a><a name="2005brasier" id="2005brasier"></a><a name="1981horodyski" id="1981horodyski"></a><a name="1981buick" id="1981buick"></a><a name="1988buick" id="1988buick"></a><a name="1992buick" id="1992buick"></a>Apex Chert </h2>
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<img src="Images/apexmap.JPG" alt="Fig 6. Location map of Apex Chert in Western Australia " width="146" height="119"><br>
<p>Fig 6. Location map of Apex Chert in Western Australia </p>
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<p>The Apex Chert is a sedimentary chert unit found within the 1.5m to 2m thick Apex Basalt formation and is found in the Pilbara Block in the northwest of Western Australia (Fig. 6). The lithologies in this area are typically sedimentary and volcanics which range from ~3 Ga to ~3.5 Ga whilst the Apex Chert itself has an age of ~3.460 Ga to ~3.470 Ga which is constrained by U-Pb zircon ages from the underlying Duffer Formation and the overlying Panorama Formation [<a href="moreinfo.html#schopf1993">Schopf, (1993)</a>].</p>
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<img src="Images/apexfossils.JPG" alt="Fig 7. Examples of microfossil taxa from the Apex " width="285" height="228"><br>
<p>Fig 7. Examples of microfossil taxa from the Apex </p>
<p>Chert [<a href="moreinfo.html#schopf1993">Schopf, (1993)</a>] </p>
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<p>The microfossils themselves are found within the dark chert beds and make up ~5% of the total rock and are thought to demonstrate key criteria for biogenicity [<a href="moreinfo.html#schopf2004">Schopf, (2004)</a>]; the fossils are indigenous to the Apex Chert, they are contained within rocks of confirmed age and are syngenetic to the deposition of the sediments. In total 11 taxa were described by <a href="moreinfo.html#schopf1993">Schopf (1993)</a>, the majority of these being dark brown to black carbonaceous microfossils (Fig 7) which are typically irregularly deposited and randomly orientated filaments which are often surrounded by dark kerogenous material. This disorganization implies that they are not stromatolitic and instead merely individual microbes which are attributed to a wave-washed beach or river mouth [<a href="moreinfo.html#schopf1999">Schopf (1999)</a>]. </p>
<p>Critics however, suggest that simple geological mapping shows that these putative microfossils were formed in hydrothermal feeder dykes and that emplacement of many of the microfossil structures was as a result of late stage fissure-filling [<a href="moreinfo.html#brasier2005">Brasier <em>et al.</em>, (2005)</a>]. .In addition to this [<a href="moreinfo.html#brasier2005">Brasier <em>et al.</em>, (2005)</a>] suggests that these microfossil structures are simply mineral reaction rims formed by the displacement of mineral impurities during devitrication and recrystallisation of hydrothermal silica and are comparable to other well-known pseudofossils of Archean and Proterozoic rocks [<a href="moreinfo.html#horodyski1981">Horodyski, (1981)</a>, <a href="moreinfo.html#buick1981">Buick <em>et al.</em>, (1981)</a>, <a href="moreinfo.html#buick1988">Buick, (1988)</a> and <a href="moreinfo.html#buick1992">Buick, (1992)</a>]. </p>
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<h2>Onverwacht Group<a name="onverwacht" id="onverwacht"></a> </h2>
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<img src="Images/onverwachtmap.JPG" alt="Fig 8. Location map of Onverwacht Group in S.A" width="143" height="180"><br>
<p>Fig 8. Location map of Onverwacht Group in S.A</p>
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<p>The island was a Celtic community which came under the rule of the Norse in 1079, this has left a legacy from the Tynwald government to many place names. After a period of alternating rule by the Kings of England and Scotland</p>
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<img src="Images/onverwacht1.jpg" alt="Fig 8. Location map of Onverwacht Group in S.A" width="308" height="378"><br>
<p>Fig 8. Location map of Onverwacht Group in S.A</p>
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<p align="center">The information contained on this website is for general information purposes only and does not represent the views and opinions of the University of Southampton or the National Oceanography Center including affliated parties. LAST UPDATED: [14 MAY 2008]</p></div>
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Have I made any blindingly obvious mistakes?? 
Originally Posted by 98kellrs
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