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Paleogeographic differences in temperature, water depth and conodont biofacies during the Late Devonian

Abstract : The Famennian (Late Devonian) started after and ended with two of the seven largest crises of the Phanerozoic, the Kellwasser and Hangenberg events, respectively. In between, global environmental trends have been identified , involving cooling and eustatic regression. Tropical and subtropical marine faunas were largely cosmopolitan. Overall, this suggests that the Famennian was marked by long-term environmental changes occurring in a relatively homogeneous manner despite being punctuated by several short-term events of limited faunal impact. How these trends were modulated according to geographic location is investigated in this study by comparing two continuous outcrops in the Montagne Noire (Col des Tribes section, France) and in Saxo-Thuringia (Buschteich section, Germany). Both were located in the subtropical area during this period and belonged to two former microcontinents bracketed between the closing Rheic Ocean and Gondwana. Sedimentary facies, oxygen isotopes, and the generic conodont composition (biofacies) were studied in a high resolution and in the same rock samples. Sedimentary facies provided an estimate of water depth and oxygen isotopes were used as pa-leotemperature proxy. Conodont biofacies were analyzed using a principal component analysis, allowing the expression of the variations in the two outcrops on the same axes, and a quantitative comparison with the other proxies. Sea-level and temperature variations were different between the two areas. Saxo-Thuringia displayed stable deep and warm conditions throughout. In contrast, the environment of the Montagne Noire was shallower and cooler during the Late and latest Famennian compared to the Early and Middle Famennian, congruent with the global change evidenced elsewhere. The location of Saxo-Thuringia, close to the first point of closure of the Rheic Ocean, might have favored active tectonics, causing a local departure from the eustatic trend. The stable temperatures at BU during the Late and latest Famennian may be due to the position of Saxo-Thuringia in the remnant Rheic Ocean, limiting water mass exchange with open seas, and favoring the persistence of warm conditions. Offshore taxa persisted later at high abundance in the Saxo-Thuringian record. The two conodont biofacies records were otherwise very comparable. This suggests that other factors mitigated the water depth forcing on these conodont assemblages.
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Soumis le : jeudi 18 octobre 2018 - 10:55:58
Dernière modification le : vendredi 18 septembre 2020 - 14:34:37

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Catherine Girard, Jean-Jacques Cornee, Michael Joachimski, Anne-Lise Charruault, Anne-Béatrice Dufour, et al.. Paleogeographic differences in temperature, water depth and conodont biofacies during the Late Devonian. Palaeogeography, Palaeoclimatology, Palaeoecology, Elsevier, 2018, ⟨10.1016/j.palaeo.2018.06.046⟩. ⟨hal-01895836⟩

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