Stratigraphic Record of Oceanic Anoxic Events Andrea Ziegler

Stratigraphic Record of Oceanic Anoxic Events Andrea Ziegler Stratigraphy 12 April 2007

Anoxic? • Oxygen depletion • Multiple reasons: – Stagnation conditions – Density stratification – Organic material input – Strong thermoclines

Oceanic Anoxic Events (OAEs) • Schlanger and Jenkyns, 1976 – Deep Sea Drilling Project from the Pacific Ocean – Black, carbon-rich shales – Same age as similar sediments from other localities – Represent unusual oceanic conditions

Lithographic Characteristics • • • Black shales and mudstones Very thinly laminated Undisturbed Anomalous amounts of organic carbon Other significant isotopic anomalies

Causes of OAEs • Change in ocean fertility – Increase in organic walled plankton/bacteria • Expanded/intensified oxygen minimum zone • Enhanced amounts of organic carbon is sediments *This hypothesis requires that there was a major climactic change on the global scale. . .

Possible Igneous Germination? • Volcanic eruption – Huge volume of CO 2 released • • • Rise in global temperature Increased weathering rates Increased fluvial nutrient flux Rise in organic productivity Increase in organic carbon burial

Mesozoic OAEs • The Early Toarcian – 183 mya • Cenomanian-Turonian – 93. 5 mya

Cenomanian. Turonian OAE Early Toarcian OAE

Mesozoic OAEs in the grand scale

Specific Characteristics • Span less than 0. 5 million years (typical for OAEs) • Proceeded by regional erosion and upwelling • Early Toarcian – More concentrated organic matter – Hydrogen rich • Cenomanian-Turonian – Less concentrated organic matter – Hydrogen poor

Conclusion • Important for many reasons – Scientific: • Paleoclimatology • Paleontology • Evolutionary Biology – Economic • Petroleum/Natural Gas reserves