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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

Published online by Cambridge University Press:  04 February 2016

JUSTYNA SMOLAREK ,
WIESŁAW TRELA ,
DAVID P. G. BOND  and
LESZEK MARYNOWSKI
JUSTYNA SMOLAREK
Affiliation:
Faculty of Earth Sciences, University of Silesia, Będzińska 60, 41–200 Sosnowiec, Poland
WIESŁAW TRELA
Affiliation:
The Polish Geological Institute – National Research Institute, Zgoda 21, 25–953 Kielce, Poland
DAVID P. G. BOND
Affiliation:
Department of Geography, Environment and Earth Sciences, University of Hull, Cottingham Road, Hull, HU6 7RX, United Kingdom
LESZEK MARYNOWSKI*
Affiliation:
Faculty of Earth Sciences, University of Silesia, Będzińska 60, 41–200 Sosnowiec, Poland Wrocław Research Centre EIT + Ltd, Stabłowicka 147, 54–066 Wrocław, Poland
*
†Author for correspondence: leszek.marynowski@us.edu.pl
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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. Total organic carbon 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, suggest oxygenated conditions prevailed. However, elevated total organic carbon 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 deposition, bottom-water conditions deteriorated from oxic during Telychian time to mostly suboxic/anoxic immediately prior to the L/W boundary, before a brief reoxygenation at the end of the Ireviken black shale sedimentation in the Sheinwoodian Stage. Rapid fluctuations in U/Mo during the Ireviken Event are characteristic of fluctuating redox conditions that culminated in an anoxic/euxinic seafloor in Sheinwoodian time. Following Ireviken black shale 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 Ireviken Event extinctions, which affected mainly pelagic and hemipelagic fauna.

Keywords

Ireviken Eventredox conditionsinorganic proxiespyrite framboidsSilurian

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Type
Original Articles
Information
Geological Magazine , Volume 154 , Issue 2 , March 2017 , pp. 247 - 264
Copyright
Copyright © Cambridge University Press 2016 

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