California State University Long Beach 

Cretaceous Greenhouse

• Mid-Cretaceous
• Superplume episode (124-83 Ma)
• Greenhouse conditions
• 4-8 times modern atmospheric CO₂ levels
• Increased weathering rates
• Increased nutrient flux to oceans
• High Sea Level
• Flooded North America and Europe
• Abundant Black Shale deposits
• Organic-rich marine sediments deposited under anoxic, stagnant conditions
• Huge oil accumulations
• 60% of known reserves
• Volcanic outpouring from core/mantle boundary
• Built numerous Pacific seamounts and plateaux
• Flood basalts on land
• Increased rates of seafloor spreading
• Also subduction related volcanism
• Abnormally long episode of stable magnetic polarity
• Cretaceous Long Normal
• May reflect increased convection in outer core

Superplumes may occur episodically

• Pennsylvanian-Permian event?
• High sea level
• Long, stable reversed magnetic polarity
• Warm
• Coal deposits
• Gas accumulations
• Earlier Paleozoic events?
• Other intervals of very high sea level
• Poor, fragmental magnetic polarity record

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Middle Miocene cooling step

• Chicken or the egg?
• Increased silicate weathering through Cenozoic
• Indicated by trend in strontium isotope ratios
• 87Sr/86Sr
• Strontium isotope variation derived from
• River influx from weathering of continental rocks
• Hydrothermal input from spreading centers
• Silicate weathering draws down atmospheric CO₂
• Entering the icehouse
• Colder temperatures slows weathering

Uplift of the Himalayas and Tibetan plateau

• Especially rapid uplift and erosion
• 21-17 Ma
• Increased mechanical and chemical weathering
• Sharp rise in ⁸⁷Sr/⁸⁶Sr ratio
• Increased flux of nutrients to the sea
• Increased fertility and productivity of phytoplankton
• Increased organic carbon burial (Monterey Formation)
• Shown by carbon isotopes
• Decreased atmospheric CO₂
• Global cooling
• Growth of Antarctic ice sheet
• Shown by oxygen isotopes

Original Monterey Hypothesis for Miocene cooling

• Tectonic movement
• Opening of Drake's Passage
• Unimpeded flow of circumpolar current
• Polar cooling
• Formation of Pacific Rim basins
• Flow of old, nutrient-rich water into Pacific
• Increased upwelling and phytoplankton productivity
• Increased preservation and burial of organic matter in restricted basins
• Drawdown of CO₂ from ocean and atmosphere
• Global cooling

Growth of Antarctic ice sheet

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