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Cenozoic Marine Tectonics

Cenozoic Marine Tectonics

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Cenozoic Marine Tectonics

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  1. Cenozoic Marine Tectonics Transitioning into the Ice House World

  2. Cenozoic Tectonism • Long-term Climate • Major Tectonic Events • Case Studies • Boundary events

  3. The Geologic Evidence • Paleontological and Paleobotanical Remains

  4. The Arctic Environment

  5. The Geologic RecordEllesmere Island

  6. Ellesmere Island 50 MaMary Dawson of the Carnegie Museum with ~50 million year old fossil of an alligator

  7. Is this Possible?

  8. Eocene Forests in the Arctic Metasequoia stumps & logs atAxel Heiberg Is.

  9. Eocene Fossils from WyomingCrocodile SycamoreBorealosuchusPlatanus wyomingensis

  10. The Arctic Then Now

  11. The Hot House to Ice House Transition • Greenhouse gases • Thermohaline circulation • Continental Configurations

  12. Greenhouse gases

  13. What caused the pCO2 to change? • High pCO2 during early Eocene could have resulted from: • Seafloor spreading changes • Large-scale volcanism

  14. High pCO2 during early Eocene • Large-scale volcanism • Brito-Artic Volcanism • Giant’s Causeway in N. Ireland • Early Tertiary age

  15. Decreasing pCO2after ~50 Ma

  16. Decreasing pCO2 after ~50 Ma • Collision began ~50 Ma • Increased weathering = Atm. CO2 decrease • CaSiO3 + CO2 = CaCO3 + SiO2

  17. Transition into Psychrosphere • In 1976, Jim Kennett and Nick Shackleton published a paper proposing that the Eocene-Oligocene boundary represented a transition into a Psychrosphere (warm surface ocean above a cold deep water mass).

  18. Thermal Isolation • In a series of papers, Kennett and Shackleton laid the grounds for a tectonic trigger - Thermal Isolation of Antartica • Two barriers cleared and allowed the Antarctic Circumpolar Current to initiate. • Tasman Rise and Drake Passage

  19. 20-Dec-1998

  20. The Southern Ocean circles the world in the Southern Hemisphere between latitudes 40 degrees and 60 degrees South. Unlike the Northern Hemisphere, there are no land masses to break up this great continuous stretch of sea water.

  21. The ACC and Climate • The ACC and its effect on climate. They find it controls climate in three ways: • 1. By connecting the world’s oceans, the ACC redistributes heat and other properties influencing the patterns of temperature and rainfall.

  22. The ACC and Climate 2. The vertical movement of water, caused by Antarctic freezing during the winter and warming during summer, controls the renewal of deep water in the worlds oceans. 3. There is an exchange of gases, such as oxygen and carbon dioxide, with the atmosphere at the sea surface. The ocean contains 50 times more carbon than the atmosphere, so the rate at which carbon dioxide is absorbed by the Southern Ocean can directly affect climate change.

  23. ODP Leg 189 Kennett and Exxon were Co-chief Scientists. Constrained the opening of this barrier to ~Eocene-Oligocene boundary

  24. Drake Passage • Modeling efforts by • Larry Lawver - UT Austin • Reconstructions by: • Peter Barker

  25. Lawver Model • Switch to AKOG PPT

  26. Lawver Model • In a conversation with Larry, I asked him when the Drake opened. • His response was: that we (paleoceanographers) would tell him. The tectonic models get you into the ball park. • The answer is: some time in the Oligocene

  27. Barker Reconstruction Argued that it is much more complicated than the Antarctic Peninsula clearing South America

  28. Barker Conclusion • Argued that Drake Passage is a Miocene event. • Best guess is 22-17 Ma

  29. Wright Analysis • In the early 1990’s, I borrowed an idea from Kennett. I looked at the distribution of sediments in the Southern Ocean recovered during DSDP and ODP drilling. • The following was published in: Wright and Miller 1993

  30. Wright Conclusions • Large-Scale Erosion: • Late Eocene • Eocene-Oligocene boundary • ‘mid’ Oligocene • Oligocene/Miocene boundary • Middle Miocene

  31. Wright Conclusions • Drake Passage: • Probably close to Oligocene/Miocene boundary • Ongoing Discussion centers on “effective” opening

  32. Glacial History • Zachos’ smoking gun: • Leg 120 drilled the Kerguelen Plateau. Zachos showed IRD and 18O increase were co-incident at Eocene/Oligocene boundary.

  33. Katabatic Winds The highest wind speeds ever recorded at sea level anywhere in the world were at Cape Denison in Adelie Land. Ninety years ago Sir Douglas Mawson landed there and dubbed the area "Home of the Blizzard" because the winds blew men off their feet. Peak gusts have been clocked moving faster than 100 mph.

  34. Katabatic Winds

  35. Antarctic Surface Water

  36. Antarctic Ice Surges • Mechanism • Ice surges out of interior of Antarctica. • Increased albedo in southern ocean causes cooling. • Predictions • Ice-rafted debris in southern ocean increases at onset of glaciation.

  37. Zachos’ results show that Antarctic Ice Sheet reached the Continental shelf. Conclusion is that part of this 18O increase is ice related.

  38. Antarctic Ice Surges Note the old time scale. 35.8 Ma = 33.5 Ma on the Berggren et al. 1995 TS

  39. Ken will cover cover the probability of ice sheets prior to the Eocene Boundary. SO GO TO HIS NOTES ON THIS.

  40. Northern Hemisphere Glaciation • Traditional view based on Shackleton landmark paper. • Northern Hemisphere glaciation began in late Pliocene - 2.6 Ma

  41. Northern Hemisphere Glaciation

  42. Northern Hemisphere Glaciation Site 659 Tiedemann et al., 1994

  43. Northern Hemisphere Glaciation • Drilling in higher latitudes reveals different story. • NHG during middle Miocene

  44. ODP LEG151

  45. The Miocene Perspective

  46. Generalization • Middle to late Miocene Northern Hemisphere Ice Sheets were small but present • ACEX drilling recovered middle Eocene (~45 Ma) that show evidence for Ice Rafting • Missing much of the record between the late Eocene and middle Miocene