Cenozoic Marine Tectonics Transitioning into the Ice House World
Cenozoic Tectonism • Long-term Climate • Major Tectonic Events • Case Studies • Boundary events
The Geologic Evidence • Paleontological and Paleobotanical Remains
Ellesmere Island 50 MaMary Dawson of the Carnegie Museum with ~50 million year old fossil of an alligator http://www.post-gazette.com/magazine/20000319dawson1.asp
Eocene Forests in the Arctic Metasequoia stumps atAxel Heiberg Is. http://www.sas.upenn.edu/earth/arctic/data.html
Eocene Fossils from WyomingCrocodile SycamoreBorealosuchusPlatanus wyomingensis
The Arctic Then Now
The Hot House to Ice House Transition • Greenhouse gases • Thermohaline circulation • Continental Configurations
What caused the pCO2 to change? • High pCO2 during early Eocene could have resulted from: • Seafloor spreading changes • Large-scale volcanism
High pCO2 during early Eocene • Large-scale volcanism • Giant’s Causeway in N. Ireland • Early Tertiary age
Decreasing pCO2 after ~50 Ma • Collision began ~50 Ma • Increased weathering = Atm. CO2 decrease • CaSiO3 + CO2 = CaCO3 + SiO2
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).
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
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.
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.
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.
ODP Leg 189 Kennett and Exxon were Co-chief Scientists. Constrained the opening of this barrier to ~Eocene-Oligocene boundary
Drake Passage • Modeling efforts by • Larry Lawver - UT Austin • Reconstructions by: • Peter Barker
Lawver Model • Switch to AKOG PPT
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
Barker Reconstruction • Argues that it is much more complicated than the Antarctic Peninsula clearing South America
Barker Conclusion • Argues that Drake Passage is a Miocene event. • Best guess is 22-17 Ma
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
Wright Conclusions • Large-Scale Erosion: • Late Eocene • Eocene-Oligocene boundary • ‘mid’ Oligocene • Oligocene/Miocene boundary • Middle Miocene
Wright Conclusions • Drake Passage: • Probably close to Oligocene/Miocene boundary • Ongoing Discussion centers on “effective” opening
Glacial History • Zachos’ smoking gun: • Leg 120 drilled the Kerguelen Plateau. Zachos showed IRD and d18O increase were co-incident at Eocene/Oligocene boundary.
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.
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.
Antarctica Ice Surges http://eosweb.larc.nasa.gov/HPDOCS/misr/misr_images/larsen_ice_shelf.jpg
Zachos’ results show that Antarctic Ice Sheet reached the Continental shelf. Conclusion is that part of this 18O increase is ice related.