Spät Devonische Events in ozeanischen Ablagerungsräumen: Beispiele aus der Mongolei
Zusammenfassung der Projektergebnisse
The disparity of information in different depositional settings and areas fundamentally hampers knowledge on climate change and faunal change during and in the aftermath of global extinction events. As a step towards addressing problems of palaeogeographic sample bias, biostratigraphy, and biodiversity we could present new results from three different sections and from two terranes within the Central Asian Orogenic Belt, which is an important contribution to understand biodiversity patterns in isolated ecosystems during times of several global climate changes, such as in the Palaeozoic. Unfortunately, a detailed study of the F/F Crisis and the Hangenberg Event was not possible as expected, which is a result of various reasons: (a) the section in western Mongolia provides strong evidence of the Hangenberg Event, but due to facies conditions (shallow-intertidal to outer ramp) and limited biostratigraphic control we have not been able to pinpoint this event exactly; (b) the second section in southern Gobi is characterized by hemipelagic palaeoenvironments but due to local tectonics and thrusting possible equivalents of the above mentioned event layers are not exposed. The D/C transition in the third section looks more promising as we have found conodonts (e.g. Protognathodus kockeli) close to the D/C boundary. Also, the lithology points to equivalent sediments of Hangenberg Crisis. Furthermore, we could mark some other Palaeozoic events such as the Hirnantian Event in the Ordovician, the Middle Devonian Chotec Event, and the Late Devonian Dasberg Crisis. The overall fauna of the studied sections differs to other successions of similar age and palaeoenvironmental settings (e.g. such as sections in Iran, Morocco, and Germany). Although fossil groups such as conodonts, ostracods, trilobites and corals and stromatoporoids yielded cosmopolitan species, the number of endemic ones is relatively high in relation of occurring species. Generally investigated groups exhibit low diversity, but large numbers of specimens (such as ostracods), whereas a most abundant and diverse fauna of Palaeozoic crinoids and blastoids was collected from the section in Mongolia. This supports the hypothesis that the CAOB was a biodiversity hotspot for Famennian echinoderms and a precursor to the very successful echinoderm communities that dominated Mississippian shallow-marine ecosystems globally. In the Chuluun Formation of the Shine Jinst section we mapped several bivalve biostromes, which most probably belong to the but Alatoconchids. The known stratigraphic distribution of the Alatoconchid family is limited so far to the Permian (Kungurian to Capitanian; see Chen et al. 2021 cum lit.). The found specimens may represent precursors (work in progress), which would document the oldest record of Alatoconchids found in the world. An Early Devonian unconformity, which is linked with a regional tectonic event led to a profound change of reef communities in the late Early Devonian in southern Mongolia. Reef organisms such as corals and stromatoporoids occur but living conditions and/or geographic isolation resulted in less successful colonization, so that reef organisms never accumulated enough to build real reefs. They grew as scattered colonies forming less densely populated biostromes. Prolonged intensive volcanic activity particularly during the Middle Devonian and Famennian in the studied sections from two different terranes support the hypothesis that volcanism might be a driver of ecological restrictions of some fossil groups in southern and western Mongolia. The overall facies development of the Shine Jinst region is similar to coeval successions described by Munkhjargal et al. (2021) for the Bayankhoshuu Ruins section in southern Mongolia (e.g. thick-bedded conglomerates). Occurring facies differences may be explained by lateral facies changes within a highly mobile depositional setting. Thus, it seems likely that both regions belong to the same tectonic unit, which is in accordance with data published by Macdonald et al. (2009) and Kröner et al. (2010). Finally, the Covid-19 pandemic hampered planned field work and laboratory studies planned to take place in 2020 so that geochemical and isotope studies are work in progress. Thus, the project was successful as it provides a number of fundamental improvements in terms of stratigraphy (new stratigraphic ranges of formations), facies/palaeoecology, biodiversity (new species described for the first time from Mongolia), and detailed information on the placement of the successions within the complex Palaeozoic Terrane scheme tor Mongolia. Results were presented in the frame of various international conferences in the U.S., Germany, and Asia. Several publications are in preparation, which will be published in the Special Series on the Devonian of Mongolia. On behalf of the international working group I would like to thank Deutsche Forschungsgemeinschaft (DFG) for their grant and the support in the frame of the Covid 19.
Projektbezogene Publikationen (Auswahl)
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Famennian crinoids and blastoids (Echinodermata) from Mongolia. Palaeobiodiversity and Palaeoenvironments, 101(3), 725-740.
Waters, J. A.; Waters, J. W.; Königshof, P.; Carmichael, S. K. & Ariuntogos, M.
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Late Devonian (Famennian) phacopid trilobites from western Mongolia. Palaeobiodiversity and Palaeoenvironments, 101(3), 707-723.
Crônier, C.; Ariuntogos, M.; Königshof, P.; Waters, J. A. & Carmichael, S. K.
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Late Devonian ostracods (Crustacea) from the Hushoot Shiveetiin gol section (Baruunhuurai Terrane, Mongolia) and their palaeoenvironmental implication and palaeobiogeographic relationship. Palaeobiodiversity and Palaeoenvironments, 101(3), 689-706.
Nazik, A.; Königshof, P.; Ariuntogos, M.; Waters, J. A. & Carmichael, S. K.
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The Hushoot Shiveetiin gol section (Baruunhuurai Terrane, Mongolia): sedimentology and facies from a Late Devonian island arc setting. Palaeobiodiversity and Palaeoenvironments, 101(3), 663-687.
Munkhjargal, A.; Königshof, P.; Hartenfels, S.; Jansen, U.; Nazik, A.; Carmichael, S. K.; Waters, J. A.; Gonchigdorj, S.; Crônier, C.; Yarinpil, A.; Paschall, O. & Dombrowski, A.
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The Mandalovoo–Gurvansayhan terranes in the southern Gobi of Mongolia: new insights from the Bayankhoshuu Ruins section. Palaeobiodiversity and Palaeoenvironments, 101(3), 755-780.
Munkhjargal, A.; Königshof, P.; Waters, J. A.; Carmichael, S. K.; Gonchigdorj, S.; Thassanapak, H.; Udchachon, M. & Davaanyam, Sh.
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Vertebrate microremains from the Late Devonian (Famennian) of western Mongolia. Palaeobiodiversity and Palaeoenvironments, 101(3), 741-753.
Roelofs, Brett; Königshof, Peter; Trinajstic, Kate & Munkhjargal, Ariuntogos
