International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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UPPER CARBONIFEROUS TO LOWER TRIASSIC CARBON ISOTOPIC SIGNATURE IN CARBONATE ROCKS OF THE WESTERN TETHYS (SLOVENIA)

Published: Aug 2003

Pages: 217 - 228

Authors: MATEJ DOLENEC, BOJAN OGORELEC, SONJA LOJEN

Abstract: The carbon isotope composition of carbonate rocks spanning an approximately 1650 m thick interval ranging from Upper Carboniferous to Lower Triassic, together with pedogenic carbonate carbon and organic carbon isotope data of Middle Permian plant remains, were used to evaluate the carbon isotope evolution of the Late Paleozoic in the Western Tethys. The results indicate a “positive carbon isotope event” across the Carboniferous-Permian (C/P) boundary, a negative shift of δ13C values at the end of the Lower Permian, a positive δ13C excursion at the Middle Permian-Upper Permian transition and the well known worldwide perturbations of the carbon cycle at the end of the Permian marked by a prominent decrease of about 4 ‰ at the Permian-Triassic (P/Tr) boundary, followed by a gradual increase of δ13C values from the Lower Scythian to the Anisian. It is suggested that the shape of the δ13C curve records changes in the carbon cycle that reflecting variations in factors such as burial rate and oxidation of organic carbon due to sea-level oscillations, which could be slightly overprinted by local processes influencing carbon isotopic composition in particular sedimentary environments. However, the marked disturbances in the carbon cycle across the P/Tr boundary most probably resulted from a combination of factors such as an accelerated oxidation of organic carbon due to the terminal phase of the Upper Permian marine regression, in combination with volcanic activity and a possible expulsion of methane from stored hydrates, as well as from a crash in primary bioproductivity.

Keywords: Western Tethys, Slovenia, Upper Carboniferous–Lower Triassic, Permian-Triassic boundary, carbon stable isotopes, carbonates

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