• 1.64 Ma

• Only 38 seconds long!

The Quaternary Period

Cenozoic Time Scale

• 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

Pleistocene—Holocene Tectonism and

Volcanism

• 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

Uplift and Deformation

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

• 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

Cascade Range

• 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

Lassen Peak—Lava Dome

• 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

Pleistocene Stratigraphy

Glaciers in North America

Glaciers in Europe

• 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

Four Glacial 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

How Many Stages?

– 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?

Correlation

•chaotic sediments difficult to correlate•minor fluctuations

• Changes in surface ocean temperature – recorded in the O18/O16 ratio in the shells of planktonic foraminifera

– provide data about climatic events

Evidence for Climatic Fluctuations

Oxygen Isotope Ratio

QUATERNARY

60 Ma

Today

~2 Ma - Northern Hemisphere

10,000

CENOZOIC ERA

~45 Ma - East Antarctic

~30 Ma - West Antarctic

Cenozoic Glaciatio

ns

Onset of the Ice Age

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

•Shut off E/W global ocean flow

Isthmus of Panama: North & South American plates collided ~ 3.5 Ma

Why the Icehouse?

Caribbean warms

Gulf Stream moves warm water north

Increases ocean evaporation and precipitation on land

Glaciers need precipitation

• 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

Pleistocene Underway

You Are Here!

But we didn’t just get ONE ice age…

We got dozens of them.

• 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?!?)

The Milankovitch Theory

Three Variables

• about 100,000 years

Ellipticity

• 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

Axis Tilt

• 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

Precession

Plane of Earth’s Orbit

• At present, Earth is closer to the Sun in January

• In about 11,000 years, closer to the Sun in July

Effects of Precession

Makes a tippy system

Convolve 100,000 + 41,000 + 26,000 years…

Pleistocene Glacial cycles

• 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

Warming Trend

• 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

Little Ice Age

Pieter Bruegel the Elder (1525–1569)

• 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

Glaciers—What Are They and How Do They 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

How do glaciers form?

Marguerite Bay, 2002

• 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

Glaciers Move

Amundsen Sea, 1999

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

Glaciation and Its Effects

• Uplift in meters – during the last 6000 years

Isostatic Rebound

in Eastern Canada

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

U-Shaped Glacial Trough

• 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

Proglacial Lakes

• 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

Characteristics of Varves

Varves with a dropstone

• 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

Moraines

Mt. Cook, 1999

• If the glacier’s terminus – should recede and then stabilize once again

– another end moraine forms

– known as a recessional moraine

Recessional Moraine

• Features seen in areas once covered by glaciers

• glacial polish – the sheen

• striations– scratches?

Glacial Features

Devil’s Postpile National Monument, California

• Glaciers typically deposit poorly sorted nonstratified sediment

Glacial 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

• 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

Changes in Sea Level

• 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

Land Bridge

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

What would happen if all glaciers melted?

Where is all that ice?

66 m is in Antarctica

Isn't it stable?

We can watch it breaking up

Anderson et al., 2002

Change is ongoing

Difficult to Predict