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Gober Paleoclimatology Presentation.Pptx 3/8/15 Objective Uplift of Tibetan Plateau v Use Paleoarchives from the Tibetan Plateau to support the uplift weathering hypothesis for global cooling as Active Driver for over the last 50 million years Cenozoic Climate Change v Hypothesis: The uplift of the Tibetan Plateau is an active driver for global cooling of the Cenozoic period By Roslyn Gober 11 February 2015 onebigphoto.com/stunning-dolomites-mountains-italy/ Cenozoic Period Cenozoic: CO2 & Climate Change Global Atmospheric Cooling CO Levels 2 v Atmospheric CO2 and global temperature decline Uplift Weathering Hypothesis v Clear relationship between climate and atmospheric CO Tibetan 2 Plateau v Need to identify driver of atmospheric CO2 removal Extensive Physical Chemical High Terrain Weathering Weathering (Beerling, 2011) 1 3/8/15 Cenozoic: Icehouse Climate Uplift Weathering Hypothesis v Benthic foraminifera Uplift is the cause of large-scale climate changes, δ18O measurements through both direct physical impacts and indirect over last 70 Myr biochemical effects v Trend toward more v Proposed by Maureen Raymo in the late 1980’s positive values of δ18O v Physical impact v Progressive cooling of deep ocean v Changes in circulation of atmosphere and ocean v Continental ice sheet v Chemical impact growth v Drawdown of atmospheric CO2 is a result of chemical weathering of silicate rocks (Raymo, 1992) (Ruddiman, 1997) Uplift Weathering Hypothesis Uplift Weathering Hypothesis Positive Feedback Negative Feedback (Ruddiman, 2014) (Ruddiman, 2014) 2 3/8/15 Criteria for Uplift Weathering Extensive High Terrain: Tibetan Plateau 1) Extensive High Terrain v Collision between India v Must be proven to be uniquely high compared to past and Asia created most geologic eras extensive plateau on Earth v 55 Myr ago 2) Unusual Physical Weathering v 2.5 million km2 v High terrain must be causing large amounts of rock fragmentation v Avg. elevation > 5 km v Marine limestones show 3) Unusual Chemical Weathering plateau was below sea level v Exposure of fresh debris must be causing high rates of 70 Myr ago chemical weathering www.standeyo.com/NEWS/06_Earth_Changes/061117.Himalaya.megaEQ.html (Ruddiman, 2014) (Ruddiman, 2014) Extensive High Terrain: Is it uniquely high? Criteria for Uplift Weathering v Cannot prove modern elevations are unusually high or extensive based on age 1) Extensive High Terrain ✔ v Must be proven to be uniquely high compared to past v India-Asia first major continental collision in 150 Myr geologic eras v Sufficient evidence that amount of high terrain is more extensive than in earlier geologic eras 2) Unusual Physical Weathering v High terrain must be causing large amounts of rock fragmentation 3) Unusual Chemical Weathering v Exposure of fresh debris must be causing high rates of chemical weathering http://www.shantitravel.com/en/tibet-travel/ (Ruddiman, 2014) (Ruddiman, 2014) 3 3/8/15 Unusual Physical Weathering Unusual Physical Weathering: Himalayan Sediments v Ocean basin sediment influx is best record of physical weathering v Increase in sediment influx in last 40 Myr v Result of two factors: v Steep Terrain v Monsoons v Uplift of Tibetan Plateau led to increased physical weathering Himalayan Sediments in Indian Ocean (Ruddiman, 2014) (Ruddiman, 2014) Unusual Physical Weathering: Monsoons Criteria for Uplift Weathering 1) Extensive High Terrain ✔ v Must be proven to be uniquely high compared to past geologic eras 2) Unusual Physical Weathering ✔ v High terrain must be causing large amounts of rock fragmentation v Differential heating of Tibetan Plateau and Indian Ocean creates powerful monsoons 3) Unusual Chemical Weathering v Exposure of fresh debris must be causing high rates of v Causes greater physical weathering chemical weathering (Ruddiman, 2014) (Ruddiman, 2014) 4 3/8/15 Unusual Chemical Weathering: Chemical Weathering of Continental Rocks 87Sr/86Sr Isotope Record in Marine Limestones v Proxy of mantle processes and continental weathering v Removes CO2 from atmosphere through v Preserved in marine carbonates hydrolysis v Isotopic composition inputs v Measure ions v Low 87Sr/86Sr Ratio: Mantle dissolved in rivers v High 87Sr/86Sr Ratio: Continental Weathering v Difficult to determine chemical v Synthetic Stratigraphic Column of marine limestones weathering rates v Continuous over past 500 million years (Ruddiman, 2014) (Edmond, 1992) Unusual Chemical Weathering: Unusual Chemical Weathering: 87Sr/86Sr Isotope Record in Marine Limestones 87Sr/86Sr Isotope Record in Marine Limestones v Increase in oceanic 87Sr/86Sr due to chemical weathering v Marine isotopic oscillations signal dampened v Seafloor spreading too slow to impact record v Weathering of Himalayas caused dramatic increase in marine isotope ratio over last Late Cenozoic increase in 87Sr/86Sr 40 Myr (Edmond, 1992) (Edmond, 1992) (Raymo, 1992) 5 3/8/15 Unusual Chemical Weathering: Unusual Chemical Weathering: 87 86 87 86 Sr/ Sr Isotope Record in Marine Limestones Sr/ Sr and Atmospheric CO2 (Ruddiman, 2014) (Garzione, 2008) Criteria for Uplift Weathering Conclusion 1) Extensive High Terrain ✔ v Global cooling and declining atm. CO2 levels in last 50 Myr v Must be proven to be uniquely high compared to past v Evidence for Uplift Weathering Hypothesis in Cenozoic: geologic eras v Creation of Tibetan Plateau 55 Myr ago 2) Unusual Physical Weathering ✔ v Increased rate of sediment influx to Indian Ocean v High terrain must be causing large amounts of rock v Increased 87Sr/86Sr Isotope Ratio in Marine Limestones fragmentation v Hypothesis Supported 3) Unusual Chemical Weathering ✔ v The uplift of the Tibetan Plateau is an active driver for global v Exposure of fresh debris must be causing high rates of cooling during the Cenozoic period chemical weathering (Ruddiman, 2014) 6 3/8/15 References Questions? v Beerling, D.J. and Royer, D.L., 2011, Convergent Cenozoic CO2 History: Nature Geoscience V. 4, p. 418-420. v Edmond, J.M., 1992, Himalayan tectonics, weathering processes, and the strontium isotope record in marine limestones: Science, V. 258, p. 594–1,597. v Garzione, C. N., 2008, Surface uplift of Tibet and Cenozoic global cooling: Geology, V. 36, p. 1003–1004. v Raymo, M.E. and Ruddiman, W.F., 1992, Tectonic Forcing of Late Cenozoic Climate: Nature, V. 359, p. 117-122. v Ruddiman, W.F., 2014, Earth’s Climate Past and Future: New York, W.H. Freeman and Company, 445 p. v Ruddiman, W. F., 1997, Tectonic uplift and climate change. New York: Plenum Press. http://www.cits.net/china-guide/places/meili-snow-mountain.html 7 .
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