The Permian-Triassic boundary in the Baghuk Mountains (Central Iran)
Zusammenfassung der Projektergebnisse
In our project, we investigate the rather recently discovered Permian-Triassic boundary sections at Baghuk Mountain (central Iran) with respect to their lithostratigraphic succession, carbonate microfacies, stable isotopes and macropalaeontological inventory (e.g. ammonoids, nautiloids, bivalves, microbial structures). The data from the new sections will be discussed in the context of other sections in central Iran with time equivalent strata such as the Hambast Mountains near Abadeh and Shahreza, sections in the Transcaucasus-NW Iran region as well as others in the western Tethys and elsewhere. Our studies are not concluded yet and publication of the results is delayed, however we are able to present results regarding a number of aspects: Lithological succession. – The sections at Baghuk Mountain show a continuous lithological record across the P-Tr boundary. There are no indications for any gap or disconformity. These sections show a similar sedimentary succession like the sections in the Julfa area, but in contrast to those the Late Permian of Baghuk is almost entirely represented by nodular limestone with only minor shale intercalations. The extinction horizon is represented by the sudden change from nodular limestone to the “Boundary Clay”, which can be perfectly correlated between the Baghuk sections and with other sections in Iran. Palaeontological succession. – During the Wuchiapingian portion of the sections, there is a gradual change from a shallower-water to a deeper-water fossil record, i.e. from brachiopodnautiloid to ammonoid-dominated communities, reflecting a deepening of the basin. While the late Wuchiapingian and early Changhsingian interval shows similar communities, there occurs a gradual decline (and demise) of biodiversity towards the end of the Permian, particularly of ammonoids and nautiloids. Geochemical succession. – The data from Baghuk Mountain show, unsurprisingly, a stratigraphic succession of the δ13Cbulk values that coincides with other regions. However, this can be regarded as further evidence for the completeness of the sections. Microbialites. – In the Triassic portion of the Baghuk Mountain sections, microbialites are diverse in scale, external morphology and internal structure. Three macroscopic morphotypes can be distinguished: (1) dome-shaped, conical and/or bulbous in shape with protuberance on top and round to ellipsoid form, (2) planar and lens- to dome-shaped with protuberance on top and (3) club-shaped and inverted conical structures with dished upper surface. Common mesostructures are dendrolite (dendritic), stromatolite (laminated), thrombolite (clotted) or leiolite (structureless, aphanitic). Club-shaped microbialites were regularly growing on bivalve or ammonoid shells as solitary structures or small communities. Thin section investigation reveals that various microbialites are accompanied with keratose demosponges. Bivalves. – In the Early Triassic strata, bivalves are the most common macrofossils. Their preservation is fairly good, but a taxonomic identification has not yet been done by us. We mapped the bivalve occurrences within the basal 36 metres of one section and semiquantitatively evaluated their numbers, their taphonomic status (articulated or disarticulated) and their depositional orientation. Ammonoids. – With a total of about 400 specimens belonging to more than 50 species collected by us in the field campaigns. The Late Permian material from Baghuk Mountain represents the most diverse Late Permian assemblage from a single locality worldwide. Apart from its diversity, the material shows a very distinct diversity pattern and provides insight of the evolutionary history of a fossil group in pre-extinction times. Nautiloids. – The high number of rather well-preserved nautiloid specimens in the Wuchiapingian part of the section was surprising and thus, a taxonomic study of the material as well as a quantitative study (morphospace and disparity analysis) will be carried out in the next future. The nautiloids do not really show an pre-extinction evolutionary pattern but their assemblages reflect, with their change of preferred morphometric properties, bathymetric and environmental changes during the Wuchiapingian.
Projektbezogene Publikationen (Auswahl)
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2016. Discerning primary versus diagenetic signals in carbonate carbon and oxygen isotope records: An example from the Permian–Triassic boundary of Iran. Chemical Geology 422: 94-107
Schobben, M., Ullmann, C. V., Leda, L., Korn, D., Struck, U., Reimold, W. U., Ghaderi, A., Algeo, T. J., & Korte, C.
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2017. Early Triassic microbialites at Baghuk Mountain (Central Iran). – Goldschmidt Conference Paris 2017
Heuer, F., Leda, L., Korn, D., Hairapetian, V. & Moradi Salimi, H.
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2017. Latest Permian carbonate-carbon isotope variability traces heterogeneous organic carbon accumulation and authigenic carbonate formation. Climate of the Past, 1635-1659
Schobben, M., van de Velde, S., Suchocka, J., Leda, L., Korn, D., Struck, U., Ullmann, C. V., Hairapetian, V., Ghaderi, A., & Korte, C.
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2017. Pre-mass extinction decline of latest Permian ammonoids. GSA conference 2017
Kiessling, W., Schobben, M., Ghaderi, A., Hairapetian, V., Leda, L. & Korn, D.
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2018. Chemostratigraphy Across the Permian‐Triassic Boundary: The Effect of Sampling Strategies on Carbonate Carbon Isotope Stratigraphic Markers. Chemostratigraphy Across Major Chronological Boundaries, 159-181
Schobben, M., Heuer, F., Tietje, M., Ghaderi, A., Korn, D., Korte, C. & Wignall, P. B.
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2018. Pre-mass extinction decline of latest Permian ammonoids. 10th International Symposium “Cephalopods – Present and Past” Fes, 26th March – 3rd April 2018
Kiessling, W., Schobben, M., Ghaderi, A., Hairapetian, V., Leda, L. & Korn, D.
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2018. Pre–mass extinction decline of latest Permian ammonoids. Geology 46 (3), 283-286
Kiessling, W., Schobben, M., Ghaderi, A., Hairapetian, V., Leda, L. & Korn, D.
