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Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: Sedimentary and geochemical controls on the Ireviken Event in a deep marine setting

Smolarek, Justyna; Trela, Wiesław; Bond, David P. G.; Marynowski, Leszek


Leszek Marynowski

Justyna Smolarek

Wieslaw Trela

Wiesław Trela


The stratigraphic variability and geochemistry of Llandovery/Wenlock (L/W) Series boundary sediments in Poland reveals that hemipelagic sedimentation under an anoxic/euxinic water column was interrupted by low density bottom currents or detached diluted turbid layers that resulted in intermittent seafloor oxygenation. TOC values and inorganic proxies throughout the Wilków 1 borehole section suggest variable redox conditions. U/Mo ratios >1 throughout much of the Aeronian and Telychian Stages, together with an absence of pyrite framboids, suggests oxygenated conditions prevailed. However, elevated TOC near the Aeronian/Telychian boundary, together with increased U/Th and V/(V+Ni) ratios and populations of small pyrite framboids are consistent with the development of dysoxic/anoxic conditions at that time. U/Th, V/Cr and V/(V+Ni) ratios, as well as Uauthig and Mo concentrations suggest that during the Ireviken black shale (IBS) deposition, bottom-water conditions deteriorated from oxic during the Telychian to mostly suboxic/anoxic immediately prior to the L/W boundary, before a brief reoxygenation at the end of the IBS sedimentation in the Sheinwoodian Stage. Rapid fluctuations in U/Mo during the Ireviken Event (IE) are characteristic of fluctuating redox conditions that culminated in an anoxic/euxinic seafloor in the Sheinwoodian. Following IBS deposition, conditions once again became oxygen deficient with the development of a euxinic zone in the water column. The Aeronian to Sheinwoodian deep-water redox history was unstable, and rapid fluctuations of the chemocline across the L/W Series boundary probably contributed to the IE extinctions, which affected mainly pelagic and hemipelagic fauna.

Journal Article Type Article
Publication Date Mar 1, 2017
Journal Geological magazine
Print ISSN 0016-7568
Electronic ISSN 1469-5081
Publisher Cambridge University Press (CUP)
Peer Reviewed Peer Reviewed
Volume 154
Issue 2
Pages 247-264
Keywords Irevekin Event; Redox conditions; Inorganic proxies; Pyrite framboids; Silurian
Publisher URL
Copyright Statement ©2015 University of Hull
Additional Information This is the author's accepted manuscript of an article published in Geological magazine, 2017, v.154 issue 2.


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