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

Abstract

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.

Citation

Smolarek, J., Trela, W., Bond, D. P. G., & Marynowski, L. (2017). Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: Sedimentary and geochemical controls on the Ireviken Event in a deep marine setting. Geological magazine, 154(2), 247-264. https://doi.org/10.1017/s0016756815001065

• Journal Article Type: Article
• Acceptance Date: Nov 23, 2015
• Online Publication Date: Feb 4, 2016
• Publication Date: Mar 1, 2017
• Deposit Date: Dec 21, 2015
• Publicly Available Date: Nov 23, 2017
• Journal: Geological magazine
• Print ISSN: 0016-7568
• Publisher: Cambridge University Press
• Peer Reviewed: Peer Reviewed
• Volume: 154
• Issue: 2
• Pages: 247-264
• DOI: https://doi.org/10.1017/s0016756815001065
• Keywords: Irevekin Event; Redox conditions; Inorganic proxies; Pyrite framboids; Silurian
• Public URL: https://hull-repository.worktribe.com/output/383267
• Publisher URL: https://www.cambridge.org/core/journals/geological-magazine/article/lower-wenlock-black-shales-in-the-northern-holy-cross-mountains-poland-sedimentary-and-geochemical-controls-on-the-ireviken-event-in-a-deep-marine-setting/F12E14EB73896AE55BA97FDFFE1FED58
• Additional Information: This is the author's accepted manuscript of an article published in Geological magazine, 2017, v.154 issue 2.
• Contract Date: Nov 23, 2017