EXAMINING THE ROLE OF VOLCANISM ON BIOTIC CHANGES AT THE CENOMANIAN-TURONIAN BOUNDARY

The Cenomanian – Turonian boundary Oceanic Anoxic Event (OAE2, 93.9 Ma), was an episode of widespread and prolonged organic carbon burial implying significant disruption to the carbon cycle. Previous studies suggest that this event was triggered by an episode of mantle plume volcanism, which injected large amounts of carbon dioxide into the atmosphere. Many calcareous marine species, including nannofossils, foraminifera, and ammonites, exhibited increased turnover rates suggesting that these abiotic changes caused significant alterations to the marine environment. The precise temporal succession of volcanism, organic carbon burial, and biotic turnover is a key target of our OAE research.

Strontium isotopes can be used to trace hydrothermal activity as non-radiogenic Sr is introduced into the ocean at hydrothermal vents, causing a negative excursion in the ⁸⁷Sr/⁸⁶Sr record. Such an excursion has been documented at the Cenomanian – Turonian boundary (Ando et al., 2009), however, the resolution of this record is insufficient to definitively conclude that volcanism predated the onset of OAE2. Trace metals have also been used to track hydrothermal plume events. The interaction of very high temperature magmatic fluids with basaltic rocks produces a distinct trace metal signal. Snow et al., (2005) discovered two trace element peaks bracketing the onset of OAE2 and suggested that hydrothermal plumes triggered the event.

We present new strontium isotope and trace metal records from a core from the western margin of the Cretaceous Western Interior Seaway. Due to the proximity of this site to the paleoshoreline, the section is highly expanded, enabling us to study the onset of OAE2 at a higher resolution than previously possible. Strontium isotopes are analyzed on the carbonate fraction of bulk samples, extracted using an acetic acid leach. Trace metals are measured on lithium metaborate fused beads using LA-ICPMS. These records of hydrothermal activity are compared to TOC and nannofossil assemblages from the same site. By studying this expanded record, we are able to isolate the biotic and abiotic events that occurred during the onset of OAE2 and move towards understanding the precise relationships between volcanism, carbon burial and biotic turnover.