1.64 Ma

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The Quaternary Period

• 1.64 Ma
• Only 38 seconds long!

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Cenozoic Time Scale
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PleistoceneHolocene Tectonism and Volcanism

• Best known for glaciation
• but also a time of volcanism and tectonic
  activity
• Continuing orogeny
• Himalayas
• Andes Mountains
• Deformation at convergent plate boundaries
• Aleutian Islands
• Japan
• Philippines

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Uplift and Deformation

• Interactions between
• North American and Pacific plates
• along the San Andreas transform plate boundary
• produced folding, faulting, and a number of
  basins and uplifts
• Marine terraces
• covered with Pleistocene sediments
• attest to periodic uplift in southern California

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Marine Terraces

• marine terraces on San Clemente Island,
  California
• each terrace represents a period when that area
  was at sea level
• highest terrace is now about 400 m above sea level

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N Ca marine terraces
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Cascade Range

• Ongoing subduction of remnants of the Farallon
  plate
• beneath Central America and the Pacific Northwest
  
• account for volcanism in these two areas
• The Cascade Range
• of California, Oregon, Washington, and British
  Columbia
• has a history dating back to the Oligocene
• but the large volcanoes now present formed during
  the last 1.6 million years

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Lassen PeakLava Dome

• Lassen Peak, a large lava dome,
• formed on the flank of an older, eroded composite
  volcano in California about 27,000 years ago
• It erupted most recently from 1914 to 1917

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Pleistocene Stratigraphy

• Began 1.6 Ma
• Ended 10,000 years ago
• Pleistocene-Holocene (Recent) boundary
• Based on
• climate change to warmer conditions concurrent
  with melting of most recent ice sheets
• oxygen isotope ratios determined from shells of
  marine organisms
• changes in vegetation

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Glaciers in North America
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Glaciers in Europe
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Four Glacial Stages

• Detailed mapping reveals several glacial advances
  and retreats
• North America had at least four major episodes of
  Pleistocene glaciation
• Each advance was followed by warmer climates
• The four glacial stages
• Wisconsin
• Illinoian
• Kansan
• Nebraskan
• named for the states of the southernmost advance

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Four Glacial Stages
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How Many Stages?

• Recent detailed studies of glacial deposits
  indicate
• there were an as yet undetermined number of
  pre-Illinoian glacial events
• history of glacial advances and retreats in North
  America is more complex than previously thought

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Correlation

• six or seven major glacial advances and retreats
  are recognized in Europe
• at least 20 major warmcold cycles can be
  detected in deep-sea cores
• Why isn't there better correlation among the
  different areas if glaciation was such a
  widespread event?

• chaotic sediments difficult to correlate
• minor fluctuations

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Evidence for Climatic Fluctuations

• Changes in surface ocean temperature
• recorded in the O18/O16 ratio in the shells of
  planktonic foraminifera
• provide data about climatic events

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Oxygen Isotope Ratio
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Onset of the Ice Age
Cenozoic Glaciations
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Why the Icehouse?

• Long-term climate drivers
• Plate tectonics
• Opening/closing of seaways
• Ocean currents are our heat and AC
• Uplift and erosion of mountains
• Weathering reduces atmospheric CO2
• Life catastrophic evolution of new capabilities
• O2
• Astronomical drivers
• Other bodies (moon, sun) pull on the Earth,
  changing its distance to the sun

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Why the Pleistocene Icehouse ?

• Long-term tectonic driver
• Redirection of ocean currents
• Isolation of Antarctica
• Collision of N and S America
• New mountains more weathering
• Mineral weathering reduces atmospheric CO2
• less CO2 less greenhouse effect

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Antarctica became isolated ocean circulation
changes, cools
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Why the Icehouse?

• Shut off E/W global ocean flow
• Isthmus of Panama North South American plates
  collided 3.5 Ma

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Glaciers need precipitation

• Caribbean warms
• Gulf Stream moves warm water north
• Increases ocean evaporation and precipitation on
  land

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Pleistocene Underway

• By Middle Miocene time
• an Antarctic ice sheet had formed
• accelerating the formation of very cold oceanic
  waters
• About 1.6 million years ago
• continental glaciers began forming in the
  Northern Hemisphere
• The Pleistocene Ice Age was underway

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But we didnt just get ONE ice age
You Are Here!
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We got dozens of them.
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The Milankovitch Theory

• Put forth by the Serbian astronomer
• Milutin Milankovitch while interned by
  Austro-Hungarians during WWI
• Minor irregularities in Earth's rotation and
  orbit
• are sufficient to alter the amount of solar
  radiation that Earth receives at 65 N
• and hence can change climate
• (criticism at the time why 65 N?!?)

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Three Variables
Ellipticity

• about 100,000 years

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Axis Tilt

• The angle between
• Earth's axis
• and a line perpendicular to the plane of its
  orbit around the Sun
• This angle shifts about 1.5
• from its current value of 23.5
• during a 41,000-year cycle

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Precession

• Earth moves around the Sun
• spinning on its axis
• which is tilted at 23.5 to the plane of its
  orbit
• Earths axis of rotation
• slowly moves
• and traces out the path of a cone in space

Plane of Earths Orbit
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Effects of Precession

• At present, Earth is closer to the Sun in January
• In about 11,000 years, closer to the Sun in July

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Makes a tippy system
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Convolve 100,000 41,000 26,000 years
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Pleistocene Glacial cycles
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Warming Trend

• 10,000-6,000 years ago, a warming trend
• pollen
• tree rings
• ice advance/retreat
• Then the climate became cooler and moister
• favoring the growth of valley glaciers on the
  Northern Hemisphere continents
• Three episodes of glacial expansion took place
  during this neoglaciation

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Little Ice Age

• The most recent glacial expansion
• between 1500 and the mid- to late 1800s
• was a time of generally cooler temperatures
• It had a profound effect on
• the social and economic fabric of human society
• accounting for several famines
• migrations of many Europeans to the New World
• Local phenomenon

Pieter Bruegel the Elder (15251569)
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GlaciersWhat Are They and How Do They Form?

• Geologists define a glacier
• as a mass of ice on land that moves by plastic
  flow
• internal deformation in response to pressure
• and by basal slip
• sliding over its underlying surface

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How do glaciers form?

• Any area receiving more snow in cold seasons
• than melts in warm seasons
• has a net accumulation over the years
• As accumulation takes place
• snow at depth is converted to ice
• when it reaches a critical thickness of about 40
  m
• it begins to flow in response to pressure

Marguerite Bay, 2002
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Glaciers Move

• Once a glacier forms
• it moves from a zone of accumulation
• toward its zone of wastage
• As long as a balance exists between the zones,
• the glacier has a balanced budget

Amundsen Sea, 1999
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Glaciation and Its Effects

• Climate itself
• Sea level change
• Sediments
• Landforms and topography
• Isostatic rebound

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Isostatic Rebound in Eastern Canada

• Uplift in meters
• during the last 6000 years

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U-Shaped Glacial Trough

• This U-shaped glacial trough
• in Montana
• was eroded by a valley glacier

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Proglacial Lakes

• Form where meltwater accumulates along a
  glacier's margin
• Deposits in proglacial lakes
• vary considerably from gravel to mud
• of special interest are the finely laminated mud
  deposits
• consisting of alternating dark and light layers
• Each darklight couplet is a varve
• representing an annual deposit

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Characteristics of Varves

• Light-colored layer of silt and clay
• formed during the summer
• The dark layer made up of smaller particles and
  organic matter
• formed during the winter when the lake froze over

Varves with a dropstone
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Moraines

• Most important glacial deposits
• chaotic mixtures of poorly sorted sediment
  deposited directly by glacial ice
• An end moraine is deposited
• when a glaciers terminus remains stationary for
  some time

Mt. Cook, 1999
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Recessional Moraine

• If the glaciers terminus
• should recede and then stabilize once again
• another end moraine forms
• known as a recessional moraine

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Glacial Features

• Features seen in areas once covered by glaciers
• glacial polish
• the sheen
• striations
• scratches?

Devils Postpile National Monument, California
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Glacial Sediment

• Glaciers typically deposit poorly sorted
  nonstratified sediment

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Cape Cod Lobe

• Position of the Cape Cod Lobe of glacial ice
• 23,000 to 16,000 years ago
• when it deposited the terminal moraine
• that would become Cape Cod and nearby islands

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Recessional Moraine

• Deposition of a recessional moraine
• following a retreat of the ice front

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Cape Cod

• By about 6000 years ago
• the sea covered the lowlands
• between the moraines
• and beaches and other shoreline features formed

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Changes in Sea Level

• Today, between 28 and 35 million km3 of water
• frozen in glaciers
• During the maximum extent of Pleistocene glaciers
• more than 70 million km3 of ice
• These huge masses of ice contained enough frozen
  water
• to lower sea level by 130 m

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Land Bridge

• Large areas of today's continental shelves were
  exposed
• The Bering Strait exposed
• Alaska connected with Siberia via a broad land
  bridge
• Native Americans and various mammals, such as the
  bison, migrated

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What would happen if all glaciers melted?

• Sea level would rise about 70 m
• many of the world's large population centers
  would be flooded

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Where is all that ice?
66 m is in Antarctica
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Isn't it stable?
We can watch it breaking up
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Change is ongoing
Anderson et al., 2002
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Difficult to Predict