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The Quaternary Period
• 1.64 Ma
• Only 38
seconds
long!
Cenozoic Time
Scale
Pleistocene—Holocene
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
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
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
N Ca marine terraces
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
Lassen Peak—Lava 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
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
Glaciers in North America
Glaciers in Europe
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
Four Glacial Stages
How Many Stages?
• Recent detailed studies of glacial deposits
indicate
– there were an as yet undetermined number of preIllinoian glacial events
– history of glacial advances and retreats in North
America is more complex than previously thought
Correlation
– six or seven major glacial advances and retreats
are recognized in Europe
– at least 20 major warm–cold 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
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
Oxygen Isotope Ratio
Onset of the Ice Age
QUATERNARY
CENOZOIC ERA
Today
10,000
~2 Ma - Northern Hemisphere
~30 Ma - West Antarctic
~45 Ma - East Antarctic
60 Ma
Cenozoic
Glaciations
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
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
Antarctica became
isolated:
– ocean circulation
changes, cools
Why the Icehouse?
• Shut off E/W global ocean flow
Isthmus of Panama: North & South
American plates collided ~ 3.5 Ma
Glaciers need precipitation
Caribbean warms
Gulf Stream moves
warm water north
Increases ocean
evaporation and
precipitation on land
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
But we didn’t just get ONE
ice age…
You Are Here!
We got dozens of them.
The Milankovitch Theory
• Put forth by the Serbian astronomer
– Milutin Milankovitch while interned by AustroHungarians 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?!?)
Three Variables
Ellipticity
• about 100,000 years
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
Precession
• Earth moves
around the Sun
– spinning on its
axis
– which is tilted at
23.5° to the plane
of its orbit
• Earth’s axis of
rotation
– slowly moves
– and traces out
the path of a
cone in space
Plane of Earth’s Orbit
Effects of Precession
• At present, Earth is closer to the Sun in January
• In about 11,000 years, closer to the Sun in July
Makes a tippy system
Convolve 100,000 + 41,000 +
26,000 years…
Pleistocene Glacial cycles
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
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 (1525–1569)
Glaciers—What 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
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
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
Glaciation and Its Effects
•
•
•
•
•
Climate itself
Sea level change
Sediments
Landforms and topography
Isostatic rebound
Isostatic
Rebound in
Eastern
Canada
• Uplift in
meters
– during the
last 6000
years
U-Shaped Glacial Trough
• This U-shaped glacial trough
in Montana
– was eroded by a valley glacier
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 dark–light couplet is a varve
– representing an annual deposit
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
Moraines
• Most important glacial deposits
– chaotic mixtures of poorly sorted sediment
deposited directly by glacial ice
– An end moraine is deposited
– when a glacier’s terminus remains stationary for
some time
Mt. Cook, 1999
Recessional Moraine
• If the glacier’s terminus
– should recede and then stabilize once again
– another end
moraine forms
– known as a
recessional
moraine
Glacial Features
• Features seen in areas once covered by glaciers
• glacial polish
– the sheen
• striations
– scratches?
Devil’s Postpile
National
Monument,
California
Glacial Sediment
• Glaciers typically deposit poorly sorted
nonstratified sediment
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
Recessional Moraine
• Deposition of a recessional
moraine
– following a retreat of the ice front
Cape Cod
• By about 6000
years ago
– the sea covered the
lowlands
– between the
moraines
– and beaches and
other shoreline
features formed
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
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
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
Where is all that ice?
66 m is in
Antarctic
a
Isn't it stable?
We can
watch it
breaking up
Change is ongoing
Anderson et al., 2002
Difficult to Predict