Stratigraphic Record of Oceanic Anoxic Events Andrea Ziegler
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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