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Pulses of enhanced continental weathering associated with multiple Late Devonian climate perturbations : evidence from osmium-isotope compositions.

Percival, L.M.E. and Selby, D. and Bond, D.P.G. and Rachocinski, M. and Racki, G. and Marynowski, L. and Adatte, T. and Spangenberg, J.E and Follmi, K.B. (2019) 'Pulses of enhanced continental weathering associated with multiple Late Devonian climate perturbations : evidence from osmium-isotope compositions.', Palaeogeography, palaeoclimatology, palaeoecology., 524 . pp. 240-249.

Abstract

Anomalously high rates of continental weathering have frequently been proposed as a key stimulus for the development of widespread marine anoxia during a number of Late Devonian environmental and biospheric crises, which included a major mass extinction during the Frasnian–Famennian transition (marked by the Upper and Lower Kellwasser horizons). Here, this model is investigated by presenting the first stratigraphic record of osmium-isotope trends (187Os/188Os) in upper Devonian strata from the Kowala Quarry (Holy Cross Mountains, Poland). Changes in reconstructed 187Os/188Os seawater values to more radiogenic compositions are documented at the base of both the Lower (~0.42 to ~0.83) and Upper (~0.31 to ~0.81) Kellwasser horizons characteristic of the Frasnian–Famennian transition, and additionally within upper Famennian shales that record a more minor environmental perturbation known as the Annulata Event (~0.20 to ~0.53). These shifts indicate the occurrence of extremely enhanced continental weathering rates at the onsets of the Kellwasser crises and during the later Annulata Event. The similarity of 187Os/188Os values in this study from Frasnian–Famennian boundary and lower Famennian strata (between 0.4 and 0.5) to those from North American stratigraphic equivalents suggests that the 187Os/188Os values record global trends. These findings support a causal relationship between increased continental weathering (and thus, nutrient supply to the marine shelf) and the environmental perturbations that occurred during numerous Late Devonian events, including both of the biospherically catastrophic Kellwasser crises as well as other, less severe, oceanic anoxic events.

Item Type:Article
Full text:(AM) Accepted Manuscript
Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.palaeo.2019.03.036
Publisher statement:© 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Date accepted:22 March 2019
Date deposited:01 April 2019
Date of first online publication:26 March 2019
Date first made open access:26 March 2020

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