Late Devonian events in open ocean environments: examples from Mongolia

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Late Devonian oceanic anoxia with extinction events have been considered ubiquitous, and ocean anoxia has been the accepted “driving force” for these marine mass extinctions. However, there is still debate about the cause/effect relationship between anoxia and extinction in the Devonian, as the epeiric seas and tectonic basins of eastern North America and Europe generally show a close association between the two, but sites elsewhere do not. Thus, our current knowledge for instance of the F/F Event and Hangenberg Crisis is limited by significant sampling bias, as most previous studies sampled equatorial epicontinental seaways or passive continental shelves, primarily from localities across Europe and North America. Thus, there is still the need to study events in many differing expressions to fully comprehend the mechanisms of global ocean anoxia and extinction, and determine the trigger mechanism(s). The Central Asian Orogenic Belt (CAOB) is a yet grossly understudied part of the story of the Late Devonian extinctions and ecosystem rebound from extinctions. That was the reason, we went to Mongolia where we studied new field sites (open ocean), in different terranes (Baruunhuurai Terrane and on the Mandalovoo– /Gurvansayhan Terrane) were these events are not necessarily associated with black shales and/or bituminous dark limestone facies. As a step towards addressing problems of palaeogeographic sample bias, biostratigraphy, biodiversity changes in the aftermath of the F/F events and the Hangenberg Crisis we could present new results from shallow-subtidal to outer ramp settings and open ocean settings within the CAOB which are important contributions to understand biodiversity patterns in isolated ecosystems during a time of global climate changes and intensive volcanic activity, which may have led to significant changes in the global climate and biosphere. But we had to deal with some limitations due to scarce conodont fauna and high physical stress environment with frequent and often voluminous pyroclastic eruptions, both hampered detailed stratigraphic records around proposed equivalents of event layers. Thus, it is planned to study new sections in the Shine-Jinst area in southern Mongolia which belong most probably to the Mandalovoo-Terrane and are therefore comparable with the Bayankhohuu Ruins section, but much likely containing better conodont-fauna. Do the estimated sea surface temperatures (SST) during a time of global climate change considerably differ from areas published elsewhere, such as in epeiric seaways and/or continental shelf deposits in site across Europe and North America? Conodonts will be used to perform carbon and oxygen isotopes around the event layers (also from earlier field campaigns) to address this aspect and compare the results with published data.