Organic carbon content and carbon isotope variations across the Permo-Triassic boundary in the Gartnerkofel-1 borehole,Carnic Alps,Austria |
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Authors: | M. E. Brookfield W. S. Wolbach A. G. Stebbins I. Gilmour D. R. Roegge |
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Affiliation: | 1.School for the Environment,University of Massachusetts at Boston,Boston,USA;2.Department of Chemistry,DePaul University,Chicago,USA;3.Department of Physical Sciences, Planetary and Space Sciences,The Open University,Milton Keynes,UK;4.Department of Chemistry,Illinois Wesleyan University,Bloomington,USA |
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Abstract: | The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from ? 24‰ to ? 28‰ in the Latest Permian which latter value persists into the Earliest Triassic after which it decreases slightly to ? 26‰. Two strongly negative peaks of > ? 38‰ in the Latest Permian and a lesser peak of ? 31‰ in the Early Triassic are too negative to be due to a greater proportion of more negative organic matter and must be due to very negative methane effects. The overall change to more negative values across the Bulla/Tesero boundary fits the relative rise in sea level for this transition based on the facies changes. A positive shift in organic carbon isotope values at the Late Permian Event Horizon may be due to an increase in land-derived organic detritus at this level—a feature shown by all Tethyan Permo-Triassic boundary sections though these other sections do not have the same values. Carbonate carbon isotope trends are similar in all sections dropping by 2–3 units across the Permo-Triassic boundary. Gartnerkofel carbonate oxygen values are surprisingly, considering the ubiquitous dolomitization, compatible with values elsewhere and indicate reasonable tropical temperatures of 60 °C in the Latest Permian sabkhas to 20–40 °C in the overlying marine transition beds. Increased land-derived input at the Late Permian Event Horizon may be due to offshore transport by tsunamis whose deposits have been recognized in India at this level. |
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