• Periodic volcanism triggered multiple Ju

    From ScienceDaily@1:317/3 to All on Fri Apr 1 22:30:36 2022
    Periodic volcanism triggered multiple Jurassic extinctions

    Date:
    April 1, 2022
    Source:
    University of Helsinki
    Summary:
    Geologists have provided critical new evidence for the timing
    of volcanic activity in the Karoo province, the largest of the
    Jurassic magma systems. The remnants of the province are widespread
    in southern Africa and Antarctica.



    FULL STORY ==========================================================================
    A group of Finnish, Swedish, and Norwegian geologists provide critical
    new evidence for the timing of volcanic activity in the Karoo province,
    the largest of the Jurassic magma systems. The remnants of the province
    are widespread in southern Africa and Antarctica.


    ========================================================================== Severe environmental crises led to a series of large-scale extinction
    events in the Jurassic period 178-186 million years (myr) ago. The
    turmoil has been ascribed to the abundant release of volcanic gases,
    but the temporal link between volcanism and extinctions has remained controversial.

    "Our results provide strong support for the view that episodic magmatism
    in the Karoo province may have been the culprit of repeated Jurassic environmental and biological crises," says Arto Luttinen from the Finnish Museum of Natural History, the leading author of the article published
    in Gondwana Research.

    "Previous dating of volcanism in the Karoo province has indicated a
    short duration of activity 182-183 myr ago. While this age coincides
    with the largest Jurassic extinction, it cannot explain the recurrent environmental crises that began millions of years earlier and continued
    long afterwards," says Luttinen, and explains that the indications of
    longer duration and periodicity of volcanism have mostly been regarded
    as unreliable due to potential methodological issues.

    Uranium-lead method needed to unveil the historic events The new ages
    were measured at the Nordsim Laboratory in Stockholm using the so-
    called uranium-lead method on sub-millimetre-sized zircon crystals
    in volcanic rocks. The production of lead from the radioactive decay
    of uranium provides the most reliable chronometer for dating ancient
    geological processes.

    At the Nordsim Laboratory, the studied crystals are drilled with a narrow
    beam of ionized particles and the ages of the tiny zircons are defined
    by mass spectroscopic measurements of the uranium and lead abundances.

    "This approach enabled us to date individual crystals formed at various evolutionary stages of long-lived magma systems," explain co-authors
    Matti Kurhila, Geological Survey of Finland, and Martin Whitehouse,
    Swedish Museum of Natural History.

    The examination of samples collected across an over 1000 kilometre long magmatic zone in Mozambique shows the previously established peak of
    activity 182-183 myr ago was preceded by volcanism 185-190 myr ago,
    and was followed by another major magmatic stage 178-181 myr ago, and
    waning activity during the subsequent several million years.

    "These results pave the way for further research on age dating and
    magmatic degassing in order to better understand the coincidence between
    Karoo volcanism and global biosphere crises," concludes Luttinen.


    ========================================================================== Story Source: Materials provided by University_of_Helsinki. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Arto Luttinen, Matti Kurhila, Riina Puttonen, Martin Whitehouse, Tom
    Andersen. Periodicity of Karoo rift zone magmatism inferred from
    zircon ages of silicic rocks: Implications for the origin and
    environmental impact of the large igneous province. Gondwana
    Research, 2022; 107: 107 DOI: 10.1016/j.gr.2022.03.005 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220401094843.htm

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