Kohlenstoff-/Sauerstoffisotopie und Sedimentologie/Faziesanalyse in ausgesuchten Zeitabschnitten im Mittleren Paläozoikum Vietnams
Zusammenfassung der Projektergebnisse
Research on mid-paleozoic anoxic events is generally concentrated around the Rheic and Panthalassic oceans. The major aim of this project was to investigate carbon and oxygen isotopes of sedimentary rocks around global event layers from selected sections in the mid-Paleozoic in northern and central Vietnam, an area that is underrepresented in terms of event research. A prerequisite was a detailed stratigraphic record that was done mainly based on conodonts. The taxonomic composition of the studied sections also allows the description of new conodont taxa. The stratigraphic framework in different sections in northeastern, and eastern Vietnam has revealed new information on five possible equivalents of well-known Devonian bio-events of different magnitude: the (?) Kačák Event, the (?) pumilio Events, the late Middle Givetian Taghanic Event, the Frasnian/Famennian Kellwasser Event, and the Devonian/Carboniferous Hangenberg Event. Most of the investigated sediments are composed of a pelagic carbonate-shale facies, comparable to other sections in the world. Some of the event layers do not exhibit typical anoxia characterized by black limestones intercalated with dark shales, such as the Frasnian/Famennian section in northeast Vietnam but exhibit geochemical excursions comparable to other sections. For this reason we also investigated a new Frasnian/Famennian section in central Vietnam to test whether the sedimentary record is comparable to those in northeastern Vietnam (geochemical investigations are in progress). Also sediments around the Hangenberg Crises differ from most other sections known in the world. The Pho Han Formation on Cat Ba Island (D/C boundary section) is primarily composed of whitish to dark gray carbonates punctuated with black shales. Scanning electron microscopy (SEM) imaging has been used to determine presence and size distribution of pyrite framboids, which serve as a proxy for water column redox conditions. Samples examined to date contain more than 7000 framboids/cm2. Between 88.5% and 97.1% of the framboids observed were less than five microns in diameter, indicating highly euxinic conditions that extended throughout the basin’s history and were not constrained to the Hangenberg Event. SEM analysis also confirms the presence of kerogen within many of the beds. Whole rock geochemistry analyses indicate a Mo spike near the D-C transition, further confirming the highly anoxic conditions around the time of the Hangenberg Event. The geochemical results also indicate clastic input stratigraphically above the Mo spike, possibly due to a major regression (consistent with the Hangenberg Event in other locations). This research shows long-term, sustained anoxia/euxinia in this ocean basin which was unexpected and which is new in terms of event research around the D/C boundary. A further important, but unexpected output of this project is based on U-Pb detrital zircon geochronology. Detrital zircons from two Devonian siliciclastic rocks, the Van Canh- and the Van Huong Formations from the Do Son Peninsular (NE Vietnam) were analysed for U, Th, and Pb isotopes by LA-SF ICP-MS techniques. The zircon cluster of both samples from the east Red River Basin as well as paleontological affinities to South China, confirms reconstructions for NE Vietnam during the early and middle Devonian close to the western Himalayas suggested by earlier studies.
Projektbezogene Publikationen (Auswahl)
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Devonian-Carboniferous transition containing a Hangenberg Black Shale equivalent in the Pho Han Formation on Cat Ba Island, northeastern Vietnam. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 404.2014, pp. 30-43.
Komatsu T., Kato S., Hirata K., Takashima R., Orata Y., Oba M., Naruse H., Tha Hoa P., Nguyen P.D., Dang H.T., Doan T.N., Nguyen H.H., Sakata S., Kaiho K., Königshof P.
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Events in the Mid-Palaeozoic: Examples from the eastern Palaeotethys (NE Vietnam). In: Mottequin B, Denayer J, Königshof P, Prestianni C, Olive S (Eds). 2015. IGCP 596-SDS Symposium, Programme and Abstracts, Brussels, 20-22 September, 2015. Strata, Sèrie 1, Communications, 16: 77-78
Königshof P, Phuong TH, Carmichael, S, Waters J, Batchelor C, Komatsu T
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Planet Earth – In Deep Time Palaeozoic Series: Devonian & Carboniferous (Schweizerbart`sche Verlagsbuchhandlung Stuttgart, Germany) 261 pp (ISBN 978-3-510-65335-5)
Suttner, T.J., Kido E., Königshof P., Waters J., Davis L., Messner F.
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Devonian events: examples from the eastern Palaeotethys (Si Phai section, NE Vietnam). Palaeobiodiversity and Palaeoenvironments,
Vol. 97. 2017, Issue 3, pp. 481–496.
Königshof, P., Narkiewicz, K., Phuong, Ta Hoa, Carmichael, S., Waters, J.
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Precluding volcanism as primary trigger for Devonian-Carboniferous global anoxia event: Implications of the Hangenberg Event in the Late Devonian Pho Han Formation, Cat Ba Island, Vietnam. Geological Society of America Abstracts with Programs, vol. 49, No 6, Paper No. 271-2, Seattle, USA.
Paschall, O., Carmichael, S., Waters, J., Königshof, P., Joachimski, M., Tahoa, P., Komatsu, T.
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U-Pb detrital zircon geochronology of sedimentary rocks in NE Vietnam: Implication for Early and Middle Devonian Palaeogeography. Vietnam Journal of Earth Sciences (ISSN: 0866-7187), Vol. 39. 2017, Issue 4, pp. 303–326.
Königshof, P., Linnemann, U., Ta Hoa, P.
