Global ocean redox changes before and during the Toarcian Oceanic Anoxic Event

Area of Science:

• Paleoceanography
• Geochemistry
• Marine Geology

Background:

• Mesozoic oceanic anoxic events (OAEs) are linked to mass extinctions and large igneous provinces.
• The Toarcian OAE is hypothesized to be triggered by the Karoo-Ferrar igneous province.
• Global extent of anoxia and euxinia during the Toarcian OAE remains poorly understood.

Purpose of the Study:

• To estimate global anoxic and euxinic seafloor areas before and during the Toarcian OAE.
• To investigate the role of ocean redox changes in marine biodiversity.
• To reconstruct ocean redox conditions using geochemical proxies.

Main Methods:

• Analysis of rhenium and molybdenum enrichments in organic-rich mudrocks.
• Utilizing mudrocks from the Fernie Formation, British Columbia.
• Application of mass balance models to estimate seafloor areas.

Main Results:

• An expansion of up to ~7% in total seafloor anoxia occurred at the onset of the Toarcian OAE.
• Anoxic conditions were predominantly euxinic (sulfide-rich).
• Seafloor anoxia contracted before the end of the Toarcian OAE.

Conclusions:

• The Toarcian OAE significantly expanded global seafloor anoxia, dominated by euxinia.
• Ocean redox dynamics during the Toarcian OAE influenced marine biodiversity.
• Rhenium data reveals global ocean redox trends mirroring biodiversity patterns.