Cenozoic Marine Tectonics

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Cenozoic Marine Tectonics

• Transitioning into the Ice House World

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Cenozoic Tectonism

• Long-term Climate
• Major Tectonic Events
• Case Studies
• Boundary events

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The Geologic Evidence

• Paleontological and Paleobotanical Remains

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The Arctic Environment
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The Arctic Environment
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The Geologic RecordEllesmere Island
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Ellesmere Island 50 MaMary Dawson of the
Carnegie Museum with 50 million year old fossil
of an alligator
http//www.post-gazette.com/magazine/20000319dawso
n1.asp
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Is this Possible?
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Eocene Forests in the Arctic Metasequoia stumps
at Axel Heiberg Is.
http//www.sas.upenn.edu/earth/arctic/data.html
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Metasequoia stumps Axel Heiberg Is.
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Eocene Fossils from WyomingCrocodile
Sycamore Borealosuchus Platanus
wyomingensis
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The Arctic

• Then
• Now

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The Hot House to Ice House Transition

• Greenhouse gases
• Thermohaline circulation
• Continental Configurations

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Greenhouse gases
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What caused the pCO2 to change?

• High pCO2 during early Eocene could have resulted
  from
• Seafloor spreading changes
• Large-scale volcanism

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High pCO2 during early Eocene

• Large-scale volcanism
• Giants Causeway in N. Ireland
• Early Tertiary age

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Decreasing pCO2 after 50 Ma
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Decreasing pCO2 after 50 Ma

• Collision began 50 Ma
• Increased weathering Atm. CO2 decrease
• CaSiO3 CO2
• CaCO3 SiO2

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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).

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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

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20-Dec-1998
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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.
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The ACC and Climate

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

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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.

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

• Modeling efforts by
• Larry Lawver - UT Austin
• Reconstructions by
• Peter Barker

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Lawver Model

• Switch to AKOG PPT

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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

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Barker Reconstruction

• Argues that it is much more complicated than the
  Antarctic Peninsula clearing South America

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Barker Conclusion

• Argues that Drake Passage is a Miocene event.
• Best guess is 22-17 Ma

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Wright Analysis

• In the early 1990s, 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

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Wright Conclusions

• Large-Scale Erosion
• Late Eocene
• Eocene-Oligocene boundary
• mid Oligocene
• Oligocene/Miocene boundary
• Middle Miocene

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Wright Conclusions

• Drake Passage
• Probably close to Oligocene/Miocene boundary
• Ongoing Discussion centers on effective opening

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Glacial History

• Zachos smoking gun
• Leg 120 drilled the Kerguelen Plateau. Zachos
  showed IRD and d18O increase were co-incident at
  Eocene/Oligocene boundary.

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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.
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Katabatic Winds
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Antarctic Surface Water
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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.

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Antarctica Ice Surges
http//eosweb.larc.nasa.gov/HPDOCS/misr/misr_image
s/larsen_ice_shelf.jpg
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Zachos results show that Antarctic Ice Sheet
reached the Continental shelf. Conclusion is
that part of this ?18O increase is ice related.
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Antarctic Ice Surges
http//www.ldeo.columbia.edu/res/fac/CORE_REPOSITO
RY/IRDslide.GIF
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Northern Hemisphere Glaciation

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

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

• Drilling in higher latitudes reveals different
  story.
• NHG during middle Miocene

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ODP LEG151
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The Miocene Perspective
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Generalization

• Middle to late Miocene Northern Hemisphere Ice
  Sheets were small but present

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Higher Frequency Climate

• The million year events.
• Miller and Wright identified a series of ?18O
  cycles with a duration of 1 to 2 million years
• Termed Oi and Mi events.

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Icehouse Events

• Miller and Wright argued that these were Ice
  Sheet Temperature
• Covariance in PF and BF records
• Correspondence to Glacial Sediments

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Northern Deep Water Circulation

• Erosion and Deposition
• Carbon Isotopes

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The Physical RecordErosion and Drifts
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Gardar DriftSnorri DriftFeni Drift
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The Eirik Drift - S. Greenland
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Erosion and Accumulation
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A North Atlantic Valve
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Greenland-Scotland RidgeMean Depth 300 m
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Mechanism to Change Mean Depth along GSRMantle
Plume Peter VogtG. Ito Modeling
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Garrett ItosModel ofMantle Plume
VariationsAnomalies Extend to 500 km from
Plume axis
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V-Shaped Ridges and Escarpments
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Anomalous Crustal Production
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Cruise V23-03 (1969) crossed the Reykjanes Ridge
10 Times. Seismic and magnetic data allow
identification and dating of V-shaped
features(Talwani et al. 1971)
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Tracing the Anomalies to Iceland16 cm/yr20
cm/yr33 cm/yr50 cm/yr100 cm/yr
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A Proxy for Mantle Plume Production
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The Messinian Salinity Crisis

• Tales from a Deep Desert

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The Messinian Deposit

• A layer of evaporites several kilometres thick
  exists in the sediments flooring the
  Mediterranean.
• The deposit is found throughout the basin.
• The layer mantles the underlying topography.
• The deposit is 5-6 My old.

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Thats Thick!

• Seawater contains 35 kg of salt per cubic metre.
• Salt has a density of 2165 kg m-3.
• Evaporation of a cubic meter of sea water
  produces a layer 1.6 cm thick.
• A layer several km thick requires a lot of sea
  water evaporation.

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So What Happened 5-6 MyBP?

• Did salt precipitate in a shallow basin that
  eventually deepened through tectonic processes?
• Did salt precipitate in deep water in the deep
  basin that we see today?
• Did salt precipitate in shallow water in the deep
  basin that we see today?

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Salt Precipitation from Sea Water

• Carbonate precipitates when seawater is
  concentrated 1.8 times.
• Gypsum precipitates when seawater is concentrated
  3.8 times.
• Halite precipitates when seawater is concentrated
  10.6 times.

CaCO3
CaSO4
NaCl
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Evaporite Basin Hydrology

• Inflow of water and salts required to form thick
  deposits.
• Seawater contains enough salt to deposit 16 m of
  salt per 1000 m of sea water.
• Thick deposits require continuous or episodic
  resupply of water and salts.

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Evaporite Basin Hydrology

• Basin restriction is required.
• Seas that exchange freely with the ocean maintain
  salinities near that of the open ocean.
• Basin restriction allows salinity to build to
  levels signficantly higher than open ocean waters.

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Mediterranean Bathymetry
http//www.unipv.it/webcib/MedBathy20800.gif
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Two Models for Evaporite Formation

• Salts precipitate from shallow water in a shallow
  basin.
• Salts precipitate from deep water in a deep basin.

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Shallow Water in a Shallow Basin

• Water fills a shallow basin when precipitation
  exceeds evaporation.
• Climate changes to drier conditions.
• Basin dries up.
• Salt deposits in centre.

www.geog.utah.edu/geoantiquities/ define.htm
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Evaporites in Deep-Water Deep Basins
Evaporation
Fresh Inflow
CaCO3
CaSO4
NaCl
Salty Outflow
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Deep Water in a Deep Basin
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Signatures of Shallow Water

• Wave bedforms in salt
• Dessication cracking
• Stromatolite fossils
• Dissolution surfaces

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Morphology of Shallow Evaporite Deposits
carbonate
gypsum
halite
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Signatures of Deep Water Formation

• Laterally extensive laminae
• Turbidites
• Little change in vertical composition

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Morphology of Deep Water Evaporites
Direction of Inflow
gypsum
halite
carbonate
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The Evaporite Layer
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Measure time for sound to travel to reflector and
back--- Two-way travel time.
Multiply by speed of sound in in medium to
estimate distance.
TWTT/(1500 m/s) 2 x thickness
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Shallow Water---Fossils

• Fossils in evaporites are shallow-water species.
• Fossils are also typical of brackish and
  freshwater environments.
• Were fossils transported to site, or are they in
  their original location?

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Shallow Water Formation

• Although not conclusive, the evidence supports
  the hypothesis that the Messinian evaporites
  formed in shallow water.
• How did shallow water evaporites get to the
  bottom of a 3000-m deep basin?

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Ways to Get Deep

• The basin deepened by tectonic processes.
• The basin dried up entirely!

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The Evaporite Layer
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Salt Layer in a Faulted Basin
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How Fast Did Infilling Occur?

• The evaporite layer shows evidence of shallow
  water.
• Immediately above it, sediments and fossils are
  typical of open ocean conditions.

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Core samples from boundary
Deep Water Oozes
Coarse Sand and Gravel
Shallow Water Evaporites
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Tale of a Giant Flood

• In the Miocene the Mediterranean, looking much as
  it does today, became isolated from the Atlantic.
• The Mediterranean dried up.
• At the end of the Miocene, a passage to the
  Atlantic re-opened, and the Mediterranean flooded
  catastrophically.

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How big was the flood?

• If you know the slope and channel dimensions of a
  river, you can calculate flow velocity.
• Discharge is flow velocity times cross-sectional
  area.

• RH hydraulic radius
• channel x-sectional area/perimeter
• slope
• n Manning roughness coefficient

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How big was the flood?

• A 6,000,000 m2
• P 24,000 m
• RH 250 m
• 1.5º
• n 0.05

U gt 100 m/s! Q gt 600,000,000 m3/s!
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Horseshoe Falls Comparison
Q 2,250 m3/s
http//www.niagarafallslive.com/Facts_about_Niagar
a_Falls.htm
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How big was the flood?

• Mediterranean holds 3.7e15 m3 of water.
• Volume divided by inflow rate yields filling
  time.
• Filling time would be several months!

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More than one Flood

• Thick evaporites require lots of sea water.
• Basin could have stayed isolated and been
  repeatedly filled by runoff.
• Or basin could have been isolated and connected
  to the Atlantic repeatedly.
• Presence of oozes interbedded with evaporites
  argues for the latter.

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Effect on global sea level

• Drying the Mediterranean would send water back to
  the worlds oceans, increasing sea level.
• Filling the Mediterranean would reduce global sea
  level.
• Magnitude of change is approximately 10 metres.

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A Spectacular Landscape
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Central American Seaway

• Complicated Tectonics
• Influence on water exchange between the Atlantic
  and Pacific

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Central American Seaway

• Show Droxler Overhead

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Water Exchange

• Benthic foraminiferal faunas indicate that the
  oceans were isolated at 1000m sometime around 10
  Ma.
• Surface Water
• exchange was
• at 4.6Ma

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Result of salinity increase affected No. Atlantic
Deep Water circulation and Climate Still Debated
Haug and Tiedemann, 1999
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Greenland to Faeroe Depths1) Itos model for
Radial Plume is Correct2) Excess Crust on
Reykjanes can be applied to GSR3) 550 km extent
of plume
Greenland to Faeroe Depths1) Itos model for
Radial Plume is Correct2) Excess Crust on
Reykjanes can be applied to GSR3) 550 km extent
of plume
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Critical Gateways

• Greenland-Scotland Ridge influences the potential
  source regions and outflow volume
• Panamanian Isthmus influences the water
  characteristics

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Lear et al., in press
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Late Cenozoic Gateways and Climate

• The Climate - Conveyor connection works for the
  Pliocene
• Strong Conveyor Warm Climates
• Weak Conveyor Cold Climates
• Also work on Milankovitch frequencies
• Mantle Plume variations allowed the GSR to act
  as a valve on the Conveyor

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Late Cenozoic Gateways and Climate

• Other Gateways were probably as important as
  well.
• Weak Conveyor during middle Miocene did not
  produce large No. Hemisphere Ice Sheets.
• Indonesia may have played role in heat and
  moisture fluxes
• The Panamanian Isthmus must have affected the
  water properties of NADW but was over-ridden by
  the GSR Valve

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Holocene Tectonics on the GSR?
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Cooler and Faster NADW?
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Early Holocene vs Modern

• Observations
• Ice on Center of Iceland 1km
• 300 m isostatic adjustment
• Coastal regions and shelves 300 m
• 100 m isostatic adjustment
• Iceland deglaciated 10 ky B.P (Volcanoes)
• Rebound completed within 1500 yrs

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Early Holocene vs ModernDifference is rapid
response of sea level vs sluggish isostatic
rebound
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Early Holocene Warmth

• Conveyor tectonics may have had a role in this
  climate event.

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The Heartbeat of Climate

• Earths climate engine is the Sun
• Small variations in solar radiation can have
  large climate effects
• Feedbacks can amplify or reduce the insolation
  changes

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The Heartbeat of Climate

• Daily Cycle

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The Heartbeat of Climate

• Daily Cycle
• Annual cycle

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What determines seasons on Earth?
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The Annual Cycle
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The Heartbeat of Climate

• Daily Cycle
• Annual cycle
• Milankovitch cycles

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Milankovitch Variations
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Milankovitch Variations

• Precession - Earths Wobble
• Obliquity - Earths Tilt
• Eccentricity - Earths Elliptical Orbit

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Precession - Earths Wobble
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Precession - 20,000 years
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Obliquity - 40,000 years
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Obliquity - 40,000 years
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Eccentricity - 100,000 years and 400,000 years
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Ceara Rise - Eq. Atlantic
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The Present and Future

• IPCC Report
• Global Temperature Changes
• Regional Patterns
• Atmospheric pCO2 Changes
• Sealevels
• Predictions

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Global Temperatures
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Regional Temperature Patterns
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Atmospheric pCO2
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Atmospheric pCO2
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Atmospheric pCO2
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Projections

• Atmospheric pCO2
• Temperature
• Sea level

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pCO2 Projections
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Temperature Forecasts
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Temperature Forecasts
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W. Antarctic Ice Sheet Collapse
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W. Antarctic Ice Sheet Collapse
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Large-scale Ice Sheet Collapse
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Sea Level Forecasts
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Climate System Inertia
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Have we ended the Pleistocene cycles?
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Conclusions

• Global Temperatures and Sea level have risen and
  will continue to rise
• The addition of Greenhouse gases may have kicked
  the Earth out of the rhythmic Glacial-interglacial
  cycles
• The climate system has a long-term memory