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Publication - Dr Armin Elsler

    Carbon isotope fluctuations and benthic environments in the north-alpine Rhaetian


    Mette, W, Korte, C & Elsler, A, 2012, ‘Carbon isotope fluctuations and benthic environments in the north-alpine Rhaetian’., pp. 123


    end-Triassic biotic crisis near to the Triassic/Jurassic boundary (TJB) is
    well-known as one of the “Big Five“ mass extinctions. The processes, which may
    have caused this crisis are still controversely discussed. A worldwide negative
    excursion of δ13C close to the TJB is thought to be
    caused either by sudden decrease in primary productivity, CO2
    outgassing during the end-Triassic CAMP volcanic activity, or the addition of
    isotopic light carbon from methan hydrates. The perturbation of the carbon
    cycle has also been documented by changes in the isotopic composition of fossil
    leaves and changes of the stomatal characters indicating a high CO2
    concentration in the atmosphere. According to these hypotheses the global T/J
    biotic crisis was a catastrophic event in the latest Rhaetian. Studies of the
    stratigraphic record of marine animal genera however suggest high extinction
    rates during Norian and Rhaetian times and the diversity decline was not just a
    result of extinction but also due to low origination rates of taxa and may thus
    not be classified as a true “mass extinction event”. According to some authors
    the “end-Triassic mass extinction” is the result of an artificial concentration
    of extinctions at the TJB due to “compiled correlation effect” in the
    literature. Recent analysis of stomatal index and density of fossil seedfern
    leaves and geochemical research on pedogenic carbonate nodules are suggestive
    of strongly rising atmospheric CO2 concentration and fluctuating climate in the
    Rhaetian. It seems therefore probable that the end-Triassic event was preceded
    by climatic change, which effected the composition and diversity of terrestrial
    and marine biota prior to the TJB interval. This hypothesis is supported by new
    carbon isotope data from the Rhaetian Kössen Formation, which point to
    perturbations of the global carbon cycle in the Late Rhaetian. The
    stratigraphic interval with the most significant
    δ13C negative shift, termed as Late Rhaetian Event
    (LRE), has been studied in detail with respect to changes of facies and
    microfossil associations. The data show that the microbenthic communities were
    largely controlled by fluctuations of oxygen concentration related to sea level
    changes but were not affected by the LRE. Palynological results however suggest
    a climatic shift towards higher humidity during this interval.

    Full details in the University publications repository