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Sustained Ocean Anoxia with a Volcanic Trigger for the Hangenberg Crisis?

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Archived version from NCDOCKS Institutional Repository http://libres.uncg.edu/ir/asu/ The Devonian-Carboniferous Boundary In Vietnam: Sustained Ocean Anoxia With A Volcanic Trigger For The Hangenberg Crisis? By: Olivia Paschall, Sarah K. Carmichael, Peter Königshof, Johnny A. Waters, Phuong H. Ta, Toshifumi Komatsu, & Allison Dombrowski Abstract The Devonian-Carboniferous transition (359 Ma) was a time of extreme climate and faunal change and is associated with the end-Devonian biodiversity crisis. The transition is characterized by transgressive/regressive cycles, which culminated in the onset of widespread ocean anoxia (the Hangenberg Black Shale event) and a remarkable sea-level fall close to the Devonian-Carboniferous boundary (the Hangenberg Sandstone event); together these are known as the Hangenberg Crisis. The Hangenberg Crisis has been documented around the globe, but the trigger mechanisms for its onset remain unknown. The Pho Han Formation on Cat Ba Island in northeastern Vietnam preserves the Devonian-Carboniferous transition and Hangenberg Crisis in a sediment- starved basinal facies on the South China carbonate platform. Although the Hangenberg Black Shale event is generally preserved as a discrete anoxic interval in Devonian-Carboniferous boundary sections of North America and Europe, the Pho Han Formation records sustained dysoxic/anoxic conditions from the Famennian (Upper Devonian) through the Tournasian (early Carboniferous), with severe anoxia (approaching euxinia) throughout the Hangenberg Black Shale event interval (as determined by trace element proxies, increased total organic carbon, and framboidal pyrite distributions). There is also significant mercury enrichment corresponding to the Hangenberg Crisis in the Pho Han Formation. The isolated paleogeography of the region suggests that the mercury is most likely sourced from distal volcanic emissions. It is therefore possible that large-scale volcanic activity acted as a trigger mechanism for the Hangenberg Crisis and biodiversity drop at the Devonian- Carboniferous transition, similar to other major mass extinction events. Paschall, O.C., Carmichael, S.K., Königshof, P., Waters, J.A., Ta Hoa, P., Komatsu, T., Dombrowski, A.D., 2019. The Hangenberg Event in Vietnam: sustained ocean anoxia with a volcanic trigger? Global and Planetary Change (Special issue on Devonian global changes - recent advances and challenges in different domains, eds. G. Racki and P. Wignall), v. 175, p. 64-81. DOI: 10.1016/j.gloplacha.2019.01.021. Publisher version of record available at: https://www.sciencedirect.com/science/article/pii/S0921818118304405?via%3Dihub Archived version from NCDOCKS Institutional Repository – http://libres.uncg.edu/ir/asu/ Paschall, O.C., Carmichael, S.K., Königshof, P., Waters, J.A., Ta Hoa, P., Komatsu, T., Dombrowski, A.D., 2019. The Hangenberg Event in Vietnam: sustained ocean anoxia with a volcanic trigger? Global and Planetary Change (Special issue on Devonian global changes - recent advances and challenges in different domains, eds. G. Racki and P. Wignall), v. 175, p. 64-81. DOI: 10.1016/j.gloplacha.2019.01.021 The copy of record is available from Elsevier https://www.sciencedirect.com/science/article/pii/S0921818118304405?via%3Dihub. The Devonian-Carboniferous boundary in Vietnam: sustained ocean anoxia with a volcanic trigger for the Hangenberg Crisis? Olivia Paschall1, Sarah K. Carmichael1,*, Peter Königshof2, Johnny A. Waters1, Phuong H. Ta3, Toshifumi Komatsu4, Allison Dombrowski1 1. Department of Geological and Environmental Sciences, ASU Box 32067 Appalachian State University, Boone, NC 28608, USA 2. Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, 60325 Frankfurt, Germany 3. Hanoi National University, 334 Nguyen Trai Str. Than Xuan Dist. Hanoi, Vietnam 4. Graduate School of Science and Technology, Kumamoto University, Kumamoto 806-8555, Japan * Corresponding author at: ASU Box 32067, Appalachian State University, Boone, NC 28608, USA. Tel.: +1 828 262 8471. E-mail address: [email protected] (S.K. Carmichael). Graphical Abstract: Highlights • The Late Devonian Pho Han Formation represents a Article history: Received 15 August 2018, sediment-starved carbonate basin on the South China Revised 22 January 2019, platform. Accepted 31 January 2019, • The Cat Co 3 section experienced long-term Available online 4 February 2019. Handling Editor: G. Racki anoxia/dysoxia in the Famennian, with euxinia during the Hangenberg Crisis. Keywords: • Hg chemostratigraphy indicates a possible volcanic Hangenberg event; Ocean anoxia; Vietnam; Devonian-Carboniferous; trigger for the end-Devonian mass extinction event. Volcanic trigger 1 Abstract The Devonian-Carboniferous transition (359 Ma) was a time of extreme climate and faunal change and is associated with the end-Devonian biodiversity crisis. The transition is characterized by transgressive/regressive cycles, which culminated in the onset of widespread ocean anoxia (the Hangenberg Black Shale event) and a remarkable sea-level fall close to the Devonian-Carboniferous boundary (the Hangenberg Sandstone event); together these are known as the Hangenberg Crisis. The Hangenberg Crisis has been documented around the globe, but the trigger mechanisms for its onset remain unknown. The Pho Han Formation on Cat Ba Island in northeastern Vietnam preserves the Devonian-Carboniferous transition and Hangenberg Crisis in a sediment-starved basinal facies on the South China carbonate platform. Although the Hangenberg Black Shale event is generally preserved as a discrete anoxic interval in Devonian-Carboniferous boundary sections of North America and Europe, the Pho Han Formation records sustained dysoxic/anoxic conditions from the Famennian (Upper Devonian) through the Tournasian (early Carboniferous), with severe anoxia (approaching euxinia) throughout the Hangenberg Black Shale event interval (as determined by trace element proxies, increased total organic carbon, and framboidal pyrite distributions). There is also significant mercury enrichment corresponding to the Hangenberg Crisis in the Pho Han Formation. The isolated paleogeography of the region suggests that the mercury is most likely sourced from distal volcanic emissions. It is therefore possible that large-scale volcanic activity acted as a trigger mechanism for the Hangenberg Crisis and biodiversity drop at the Devonian- Carboniferous transition, similar to other major mass extinction events. 1. Introduction The Devonian-Carboniferous (D-C) transition and conodont biostratigraphy that have not yet been concluded mass extinction is characterized as a period of severe at the time of this writing, the section studied in this paper ecological crisis, with major biotic and palaeoenvironmental will use a biostratigraphic correlation scheme based on the changes in both terrestrial and marine ecosystems. The zonations from Kaiser (2009), Ziegler and Sandberg extinction eliminated about 20% of marine invertebrate (1990), and Spalletta et al. (2017) (Fig. 1). genera, and primarily decimated pelagic organisms such as The D-C transition is not only associated with a mass fish and cephalopods, reducing long-term biodiversity of all extinction, but also a time of marine regression and vertebrates by 50% (Sandberg et al., 2002; Sepkoski, 1996; widespread oceanic anoxia, called the Hangenberg Crisis. Walliser, 1996). The ecological severity index by McGhee The Hangenberg Crisis has been recognized in sediments et al. (2013) characterizes the end Devonian extinction as from epicontinental basins and continental margins around the fourth most severe mass extinction event in Earth's the world (see reviews by Becker et al., 2016; Kaiser et al., history. 2016). It can be subdivided into the Hangenberg Black Historically, the D-C boundary has been defined via Shale (HBS) event, which is marked by widespread conodont biostratigraphy from the Global Stratotype deposition of black shale, and the regressive Hangenberg Section and Point (GSSP) location La Serre Trench E’ Sandstone (HSS) event, which at times is only visible in the section in the Montagne Noire, France, where it is based on rock record as an unconformity (Bábek et al., 2016; Cole et the first appearance of the basal Carboniferous conodont al., 2015; Kaiser et al., 2016). The global regression Siphonodella sulcata (Flajs and Feist, 1988; Paproth et al., associated with the HSS Event appears to be related to 1991). However, these early siphonodellids are difficult to continental icesheet growth in South America (Caputo et identify due to taxonomic uncertainties (Kaiser and al., 2008; Isaacson et al., 1999; Lakin et al., 2016; Streel et Corradini, 2011), and Siphonodella sulcata is also found al., 2000), North Africa (summarized in Isaacson et al., below the level that defines the La Serre GSSP (Kaiser, 2008) and mountain glaciers in the Appalachians of North 2009). Furthermore, there is concern that the La Serre America (Brezinski et al., 2010; Brezinski et al., 2009). sediments have been reworked and are not correlatable to Aside from a general agreement regarding a glacially other sections (Sandberg and Ziegler, 1996; Ziegler and influenced regression to explain the HSS Event, the Sandberg, 1994). Therefore, the D-C boundary needs to be mechanisms that triggered the anoxia of the HBS Event reevaluated, either via new biostratigraphic indicators and related extinction at the D-C boundary are still debated (Aretz, 2013; Corradini et al., 2017) or via a combined (Caplan
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