stable isotope data from European successions

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Jul 13, 2018 - The suggested level of the Annulata Event in the Pseudopolygnathus granulosus (= Upper trachytera) Zone at Geuser (Franconia, Germany) is ...
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5 International Paleontological Congress – Paris, 9 -13 July 2018

Environmental changes during Famennian low-order biocrises - stable isotope data from European successions 1

Sven Hartenfels * , Sandra Kaiser†, Michael Joachimski, Catherine Girard, Tomáš Kumpan 1

Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster – Münster, Germany

The middle to uppermost Famennian comprises repeated successions of low-order bioevents, the so-called Annulata, Dasberg and Epinette/Etroeungt (Ep/Et) events or crises. They are characterized by extinctions, originations, and radiations of selected faunal groups. These intervals coincide with transgressive/regressive pulses and the deposition of black shales and/or organic-rich limestones elsewhere. Our study focusses on stable isotope geochemistry (δ18Ophosph, 13Ccarb) from paleogeographically different pelagic limestone sections in Europe in order to reconstruct environmental changes during these biocrises. The suggested level of the Annulata Event in the Pseudopolygnathus granulosus (= Upper trachytera) Zone at Geuser (Franconia, Germany) is characterized by a weak positive peak in 13Ccarb with values of up to 2.6 . At Beringhauser Tunnel (Rhenish Massif, Germany), the 13Ccarb values are generally low, and partly influenced by diagenesis, as reflected by negative values. However, highest values of more than 2.5, were measured in the Lower Annulata Limestone. Results at Geuser and Křtiny (Moravian Karst, Czech Republic) indicate a minor but distinct 13Ccarb excursion during the Ep Event in the Bispathodus aculeatus aculeatus (= Middle expansa) Zone, with isotope ratios ˜ 2.8 . The 13Ccarb values remain relatively high in strata equivalent to the Et Event in the B. ultimus ultimus (= Upper expansa) Zone. At Col de Tribes (Montagne Noire, France) and Křtiny, 13Ccarb values are also slightly higher in strata equivalent to the Et Event, with isotope ratios > 2.8. While the temperature variations at Beringhauser Tunnel are minor, with δ18Ophosph values from coeval conodonts between 17.5 and 18.0 below, above and around the Annulata events, δ18Ophosph values from Geuser vary between 16.7 and 18.9 . Highest values at Geuser are reported from the Annulata and Ep/Et events, while the lowest values, and thus the warmest sea water temperatures, are recorded from the Polygnathus styriacus (= Lower postera) and B. stabilis stabilis (= Lower expansa) zones. Although environmental changes and their impact on faunas during the studied crises are minor in magnitude when compared to the major biocrises in the late Frasnian (Kellwasser events) and at the Devonian-Carboniferous boundary (Hangenberg Event), this study could provide insights into the causes of repeated successions of low-order bioevents during the Famennian.

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Speaker Corresponding author: [email protected]

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