Paleoredox chemistry of Cenomanian–Coniacian black shales at high paleolatitudes: Implications for the extent of anoxia during OAE2

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Marc Lenniger, Henrik Nøhr-Hansen, Len V Hills, Christian J. Bjerrum

Cretaceous oceanic anoxic events (OAEs) have been studied in detail during the last decades. OAE2 is of particular interest as it reflects one of the largest perturbations of the global carbon cycle in the Mesozoic. It is characterised by a
widespread deposition of organic rich sediments which is reflected by a positive carbon isotope excursion (CIE) in the terrestrial and marine record. Whereas the paleoredox conditions in low and mid-paleolatitudes are well constrained
for OAE2, data from high paleolatitudes are still scarce.
The paleoceanographic response at high paleolatitudes during OAE2 is here characterized by samples from Axel Heiberg Island in Canada. Preliminary palynological analyses indicate a Late Cenomanian!Coniacian age for the section.
Bulk organic carbon isotope data have been corrected using the hydrogen index (Rock Eval pyrolysis) to account for changes in organic matter sourcing. Our corrected isotope record correlates in detail with the European carbonate
reference curve and confirms our biostratigraphic model. Iron speciation (FeHR/FeT and FePy/ FeHR) data point to anoxic but non-euxinic conditions at high paleolatitudes during OAE2.
Furthermore the Sverdrup Basin was intermittently suboxic to anoxic (ferruginous) throughout most of the latest Cenomanian–Coniacian. Despite very high TOC (>10%) and hydrogen index values, molybdenum concentrations are
relatively low during OAE2 but increase after the event. This suggests a global drawdown of the seawater molybdenum reservoir caused by the widespread extent of ocean anoxia/euxinia in the Cretaceous oceans during OAE2.
Original languageEnglish
JournalMineralogical Magazine
Volume77
Issue number5
Pages (from-to)1585
Number of pages1
ISSN0026-461X
DOIs
Publication statusPublished - 2013

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