Magnetostratigraphy and the Permian Mass Extinction
Wednesday, 6. May 2009, 13:46:18
Magnetostratigraphy is a field within stratigraphy that studies the magnetic characteristics of rock bodies. If the magnetic properties of rocks have measurable differences stratigraphically, that is, from one strata to the next, those differences can be used to identify their relationships and identify varying stratigraphic units. Stratigraphic units are known collectively as magnetostratigraphic units (magnetozones). The most useful magnetic property for magnetostratigraphy results from a change in the direction of the magnetization of the rocks. Crystals in rocks are magnetically aligned with the Earth’s magnetic field. The Earth’s magnetic field has changed over the eons and those magnetic alignments are ‘recorded’ in the crystals of rocks because the rocks become magnetized in the direction of the Earth's magnetic field at the time of their formation. The change in the earth’s magnetic fields is caused by reversals in the polarity of the Earth's magnetic field, the Earth’s magnetic poles literally change locations. These reversals of Earth’s polarity have taken place many times during geologic history. (http://en.citizendium.org/wiki/Magnetostratigraphy)
The long procedure of sampling and analysis required to obtain a reversal stratigraphy for a succession of sedimentary rocks means that this technique is normally only used when other (biostratigraphic) methods cannot be used or a high-resolution stratigraphy is required. (Gary Nichols, Sedimentology & Stratigraphy, Blackwell, 1999)
Permian-Triassic gap in the fossil record?
Magnetostratigraphy has now been used to determine whether there was a Permian-Triassic gap in the fossil record of the Russian Ural Mountains.
The world’s single most severe mass extinction event which took place at the end of the Permian and start of the Triassic ages, some 250 million years ago. The extinction event, thought to be the result of runaway global warming, wiped out between 80-95 per cent of the planet’s species. Was this extinction event a real biological catastrophe or was it merely the result of gaps in the fossil record? So far it was thought that ten million years worth of rock from around that time was missing in Russia (we are talking about the continental uppermost Permian Russian stages, the Kazanian and Tatarian).
The scientists matched the magnetic record fossilised within the disputed Russian rocks with those from the rest of the World, demonstrating that the Russian rocks do indeed record the run-up to the event and the Permian/Triassic boundary and therefore the fossil losses in these rocks are part of the mass extinction.The sampled sections span the upper Guadalupian to Induan stages without any obvious break, so confirming the traditional view that the Tatarian is Late Permian in age.
Yet another piece matching in a larger jigsaw puzzle.
Reference:
Taylor et al.
Magnetostratigraphy of Permian/Triassic boundary sequences in the Cis-Urals, Russia: No evidence for a major temporal hiatus
Earth and Planetary Science Letters
Volume 281, Issues 1-2, 30 April 2009, Pages 36-47
doi:10.1016/j.epsl.2009.02.002
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4VS3P43-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=26333ea71795423cab79750f8e75508d
• http://www.bris.ac.uk/news/2009/6320.html
The long procedure of sampling and analysis required to obtain a reversal stratigraphy for a succession of sedimentary rocks means that this technique is normally only used when other (biostratigraphic) methods cannot be used or a high-resolution stratigraphy is required. (Gary Nichols, Sedimentology & Stratigraphy, Blackwell, 1999)
Permian-Triassic gap in the fossil record?
Magnetostratigraphy has now been used to determine whether there was a Permian-Triassic gap in the fossil record of the Russian Ural Mountains.
The world’s single most severe mass extinction event which took place at the end of the Permian and start of the Triassic ages, some 250 million years ago. The extinction event, thought to be the result of runaway global warming, wiped out between 80-95 per cent of the planet’s species. Was this extinction event a real biological catastrophe or was it merely the result of gaps in the fossil record? So far it was thought that ten million years worth of rock from around that time was missing in Russia (we are talking about the continental uppermost Permian Russian stages, the Kazanian and Tatarian).
The scientists matched the magnetic record fossilised within the disputed Russian rocks with those from the rest of the World, demonstrating that the Russian rocks do indeed record the run-up to the event and the Permian/Triassic boundary and therefore the fossil losses in these rocks are part of the mass extinction.The sampled sections span the upper Guadalupian to Induan stages without any obvious break, so confirming the traditional view that the Tatarian is Late Permian in age.
Yet another piece matching in a larger jigsaw puzzle.
Reference:
Taylor et al.
Magnetostratigraphy of Permian/Triassic boundary sequences in the Cis-Urals, Russia: No evidence for a major temporal hiatus
Earth and Planetary Science Letters
Volume 281, Issues 1-2, 30 April 2009, Pages 36-47
doi:10.1016/j.epsl.2009.02.002
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4VS3P43-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=26333ea71795423cab79750f8e75508d
• http://www.bris.ac.uk/news/2009/6320.html
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