Die Perm-Trias Grenze und die Untertrias transkaukasischer und zentraliranischer pelagischer Profile
Zusammenfassung der Projektergebnisse
In our project, we looked for quantitative evidence for climatic and environmental changes, which characterize the transition from the Palaeozoic into the Mesozoic. The study concentrates on better resolving the causes and causal relationships, which are responsible for the end-Permian mass extinction, the largest mass extinction of the Phanerozoic. This is achieved by investigating the geochemical signatures locked in the sedimentary rocks and their fossil content of sections in north-western and Central Iran. The geochemistry of sedimentary rocks as well as fossil organisms and their shells is known to archive information about the physical and chemical parameters of the ambient environment in which the studied minerals were precipitated. Excursions in geochemical records visualized by isotopic analysis of conodont apatite, carbonate-associated sulphate and bulk-sedimentary rock, straddling the Permian-Triassic interval, are indicative of profound climatic and environmental changes. The oxygen isotope record from conodonts strongly supports an abrupt warming event paralleling the end-Permian mass extinction. This climate change is associated with synergistic effects acting on global warming and corroborates with a scenario of a more active hydrological cycle and subsequent increase of weathering fluxes from the continent, possibly documented as a contemporaneous lithological change in the studied sections to more clay-rich deposits. Simultaneous sulphur and oxygen isotope fluctuations measured in sulphate, which is structurally substituted in carbonate, provides an insight into the sulphur biogeochemical cycle within the extinction interval. A change towards increased organic matter production and consequential re-mineralization by sulphate-reducing bacteria is a scenario that can explain the patterns observed in the isotope proxies from sulphate associated with carbonate. This is likely linked to eutrophication of marine shelf settings by large fluxes of terrestrial material entering the ocean, a potential effect of climatic warming. These observations underline the interactions between Earth surface processes and imply proximal causes, such as thermal stress and widespread marine anoxia as well as euxinia, as drivers behind the mass extinction. The findings presented in this study cannot unequivocally be assigned to an ultimate cause for the environmental and biotic catastrophe in the latest Permian. However, large-scale volcanism related to time-equivalent emplacement of Siberian trap basalts is a likely culprit that could have initiated this CO2 induced climate catastrophe. A volcanic injection of isotopically depleted carbon into the ocean/atmosphere could explain the long-term negative carbon isotope excursion of the studied marine bulk-carbonate rock. This carbon isotope pattern is similar to that observed at other localities worldwide. However, the observation of second-order variability among bulkrock δ13C curves at different localities and spatial heterogeneity in diagenetic processes urges a critical view of the fidelity of these records. This observation raises questions about the time-resolution at which palaeodata can be reliably read from carbon isotope records based on measurements from marine bulkcarbonate rock. This later example demonstrates that all the physical and chemical processes that acted upon these ancient rocks, before and after deposition, must be considered when interpreting their geochemical signals. It is shown that obtaining a reliable palaeodata record requires sufficient screening of the geochemical dataset for effects of post-depositional alteration. A good approach used on the studied material was a comparison of different chemical species as well as different mineralogical phases, such as conodont apatite and calcite brachiopod shells. In addition, it is shown that palaeoenvironmental interpretations are strengthened by comparison with results from numerical models.
Projektbezogene Publikationen (Auswahl)
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(2013): A first Late Permian fish fauna from Baghuk Mountain (Neo-Tethyan Shelf, central Iran). – Bulletin of Geosciences, 88 (1): 1-20
Hampe, O., Hairapetian, V., Dorka, M., Witzmann, F., Akbari, A.M. & Korn, D.
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(2013): Extinction Space - a method for the quantification and classification of changes in morphospace across extinction boundaries. – Evolution 67 (10): 2795-2810
Korn, D., Hopkins, M.J. & Walton, S.A.
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(2014): Faunal change near the end-Permian extinction: the brachiopods of the Ali Bashi Mountains, NW Iran. – Rivista Italiana di Paleontologia e Stratigrafia 120: 27-59
Ghaderi, A., Garbelli, C., Angiolini, L., Ashouri, A.R., Korn, D., Rettori, R. & Gharaie, M.H.M.
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(2014): High-resolution stratigraphy of the Changhsingian (Late Permian) successions of NW Iran and the Transcaucasus based on lithological features, conodonts and ammonoids. – Fossil Record 17: 41-57
Ghaderi, A., Leda, L., Schobben, M., Korn, D., & Ashouri A.R.
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(2014): Lithostratigraphy and carbonate microfacies across the Permian-Triassic boundary near Julfa (NW Iran) and in the Baghuk Mountains (Central Iran). – Facies, 60: 295- 325
Leda, L., Korn, D., Ghaderi, A., Hairapetian, V., Struck, U. & Reimold, W.U.
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(2014): Palaeotethys seawater temperature rise and an intensified hydrological cycle following the end- Permian mass extinction. – Gondwana Research, 26: 675-683
Schobben, M., Joachimski, M. M., Korn, D., Leda, L. & Korte, C.
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(2015): Flourishing ocean drives the end-Permian marine mass extinction. – Proceedings of the National Academy of Sciences of the United States of America, 112 (33): 10298-10303
Schobben, M., Stebbins, A., Ghaderi, A., Strauss, H., Korn, D. & Korte, C.
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(2015): The ammonoids from the Late Permian Paratirolites Limestone of Julfa (East Azerbaijan, Iran). – Journal of Systematic Palaeontology, 2015: 1-50
Korn, D., Ghaderi, A., Leda, L., Schobben, M. & Ashouri, A.R.
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(2016): Uncovering palaeo-environmental information from bulk carbonate δ13C of Permian-Triassic ‘Boundary Clay’ sections. – Chemical Geology, 422: 94-107
Schobben, M., Ullmann, C.V., Leda, L., Korn, D., Struck, U., Reimold, W.U., Ghaderi, A. & Korte, C.
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Permian Calcareous algae from the Khachik Formation at the Ali Bashi Mountains, NW of Iran. – Arabian Journal of Geosciences (2016) 9: 699
Ghaderi, A., Khalil Abad, M.T., Ashouri, A.R. & Korn, D.
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(submitted): Volatile Early Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate? – Palaeogeography, Palaeoclimatology, Palaeoecology 486, 15 November 2017, Pages 74-85
Schobben, M., Stebbins, A., Algeo, T., Strauss, H., Leda, L., Haas, J., Struck, U., Korn, D. & Korte, C.
