Abstract

New 40Ar/39Ar geochronology and global cyclostratigraphic calibration provide high-resolution insights into the timing of geochemical fluctuations across oceanic anoxic event II (OAE II). Five new 40Ar/39Ar data from a single section in western Canada suggest an age of 96.4 ± 1 Ma for the Cenomanian-Turonian (C-T) boundary. This is ∼3 m.y. older than previously dated. Time-series analysis (e.g., wavelet transform) reveals that OAE II was synchronously deposited worldwide over a period of ∼320 k.y. The preservation and stationarity of Milankovitch cyclicity in sections across the Atlantic indicates that no major fluctuations in sedimentation rate occur across the OAE II, except for a minor short- term decrease in the rate just before the C-T boundary. A δ13Corg increase of >2‰ took place at the beginning of OAE II over a period of ∼110 k.y., and likely represents a period of worldwide excessive organic carbon burial during transgression, leading to a 12C depletion of seawater and sedimentation. This interval was followed by a three-step decrease to pre-OAE II δ13C values.

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