R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
Terrestrial Stratigraphy
Deep-Sea Stratigraphy
Climates of the Pleistocene and Holocene
Glaciers—How Do They Form?
Glacial Landforms
Changes in Sea Level
PERSPECTIVE Waterton Lakes National Park, Alberta, and Glacier National
Park, Montana
Glaciers and Isostasy
Pluvial and Proglacial Lakes
The Milankovitch Theory
Short-Term Climatic Changes
The following content objectives are presented in Chapter 17:
 The Pleistocene and the Holocene or Recent epochs encompass only the most recent
1.8 million years of Earth history.
 The Pleistocene Epoch, lasting from 1.8 million years to 10,000 years ago, is best
known for widespread glaciers but was also a time of continuing orogeny and
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
 Much of our information about Pleistocene climates comes from oxygen isotope
ratios, pollen analyses, and the distribution and coiling directions of planktonic
 Pleistocene continental glaciers were present on the Northern Hemisphere continents
as well as Antarctica, and thousands of small glaciers were in mountain valleys on all
 Sea level fell and rose during the several Pleistocene advances and retreats of
glaciers, depending on how much water from the ocean was frozen on land.
 The tremendous weight of continental glaciers caused Earth’s crust to subside into the
mantle and to rise again when the glaciers wasted away.
 Many now-arid regions far from glaciated areas supported large lakes as a result of
greater precipitation and lower evaporation rates during the Pleistocene, and
numerous other lakes formed along the margins of glaciers.
 A current widely accepted theory explaining the onset of ice ages relies on
irregularities in Earth’s rotation and orbit.
 Important Pleistocene mineral resources include sand and gravel, diatomite, peat, and
placer deposits of gold.
To exhibit mastery of this chapter, students should be able to demonstrate comprehension
of the following:
 plate tectonics’ role in shaping the paleogeography and climate of the Pleistocene and
Holocene epochs
 the methods used to determine Pleistocene climatic changes
 characteristics and recognition of the glacial and interglacial stages in North America
 the methods used to determine oceanic temperature changes and difficulties in
correlation of marine and terrestrial deposits for the Pleistocene Epoch
 effects of glaciation upon Earth's surface
 the North American Great Lakes’ geologic history
 the proposed hypotheses for the causes of glacial and interglacial periods
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
1. The most recent part of geologic time is the Pleistocene (1.8 million to 10,000
years ago) and the Holocene or Recent epochs (10,000 years ago to the present).
Enrichment Topic 1. Louis Agassiz and the History of Geology
When Louis Agassiz first proposed his hypothesis of glaciation, he encountered
geologists who could not conceive of glacial processes having once operated in an area
where ice was no longer present. One geologist who ascribed to the concept of
diluvium—or the sedimentation processes caused by an ancient, Noachian deluge—was
William Buckland, the first professor of geology at Oxford. However, Buckland kept an
open mind, and after Agassiz showed him erratics, moraines, striations, and roches
moutonnées, he changed his beliefs from the diluvial theory to support Agassiz’s glacial
theory. It was reported that, at an 1840 meeting of the Geological Society of London,
Buckland admitted that he set out from Neufchatel to discount the glacial theory, but had
instead become converted through Agassiz’s evidence. It was more often the case that the
early hypotheses were met with rejection, and only after considerable debate were they
accepted. Brock, “The Rev. William Buckland, the First Palaeoecologist,” Biologist,
1993 v.40 n.4 p.149-152.
2. Although the Pleistoceone is best known for widespread glaciers, it was also a time
of volcanism and tectonism.
Figure 17.1 Continental Glaciers, Ice Caps, and Valley Glaciers
Figure 17.2 Pleistocene Uplift and Tectonism
Figure 17.3 Pleistocene and Recent Volcanism
3. Pleistocene glaciers covered about 30% of the land surface, and were widespread
on the Northern Hemisphere continents.
Figure 17.4 Centers of Ice Accumulation and Maximum Extent of Pleistocene
4. At least four intervals of extensive Pleistocene glaciation took place in North
America, each separated by interglacial stages. Fossils and oxygen isotope data
indicate about 20 warm-cold cycles occurred during the Pleistocene.
Figure 17.5 Pleistocene Glaciers in North America
Figure 17.6 Climatic Changes During the Cenozoic
Figure 17.7 Pollen Analysis and Climate
5. Areas far beyond the ice were affected by Pleistocene glaciers: Climate belts were
compressed toward the equator, large pluvial lakes existed in what are now arid
regions, and sea level was as much as 130 m lower than now.
Figure 17.8 The Greenland Ice Sheet
Figure 17.9 Erosion by Continental and Valley Glaciers Yields Distinctive
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
6. Moraines, striations, outwash, and various other glacial landforms are found
throughout Canada, in the northern tier of states, and in many mountain ranges
where valley glaciers are present.
Figure 17.10 Origin of End Moraines and Outwash
Figure 17.11 Terminal and Recessional Moraines in the Mid-Continent Region
Figure 17.12 The Geologic Evolution of Cape Cod, Massachusetts, and Nearby
Areas During the Ice Age
Figure 17.13 The Bering Land Bridge
7. The tremendous weight of Pleistocene glaciers caused isostatic subsidence of
Earth’s crust. When the glaciers melted, isostatic rebound began and continues
even now in some areas.
Figure 17.14 Glaciers and Isostasy
8. During times of ice accumulation, large pluvial lakes existed in now arid areas
because of greater precipitation and overall cooler temperatures, which lowered the
evaporation rate. In contrast to pluvial lakes, which formed far from the areas of
glaciation, proglacial lakes form where meltwater accumulates along a glacier’s
margin. The Great Lakes formed when advancing glaciers deeply eroded the area.
As the glaciers melted and retreated, the lakes formed with water.
Figure 17.15 Pleistocene Lakes in the Western United States
Figure 17.16 Glacial Lake Missoula was a Proglacial Lake, Whereas Lake
Bonneville was a Pluvial Lake
Figure 17.17 Four Stages in the Evolution of the Great Lakes
9. Major glacial intervals separated by tens or hundreds of millions of years probably
stem from changing positions of plates, which in turn profoundly affect oceanic and
atmospheric circulation patterns.
10. According to the Milankovitch theory, minor changes in Earth’s rotation and orbit
bring about climatic changes that produce glacial-interglacial intervals.
Figure 17.18 According to the Milankovitch Theory, Minor Irregularities in
Earth’s Rotation and Orbit May Affect Climatic Changes
11. The causes of short-term climatic changes such as occurred during the Little Ice
Age are unknown; two proposed causes are variations in the amount of solar energy
and volcanism.
Figure 17.19 Glaciers in the Cascade Range
Enrichment Topic 2. The CO2 Culprit
For many years, researchers have questioned whether humans will have a major impact
on climate change. It has long been proposed that rising carbon dioxide levels will cause
global warming, and these increased CO2 levels are attributed to the Industrial Revolution
and the burning of fossil fuels. However, some scientists offered rebuttals about the
impact of humans on CO2 levels, as well as the role that humans play in CO2 production.
(“The Holocene CO2 Rise: Antropogenic or Natural?” Eos, Jan. 2006, v.87 n.3 p.27.)
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
Several researchers (Royer, Berner, Montanez, Tabor, and Beerling) reviewed geologic
records of CO2 and glaciations and demonstrated that CO2 was low (<500 ppm) during
periods of continental glaciation, and higher (>1000 ppm) during warmer periods. (“CO2
as a Primary Driver of Phanerozoic Climate,” GSA Today, March 2004 v.14 n.3 p.4-10) It
is predicted by some geologists that twice the CO2 level will exist in the atmosphere by
2100. (“No Easy Way Out of the Greenhouse,” Discover, Oct. 2005, v.26 n.10 p.30-31)
If the global warming predictions are correct, then humans could possible suffer adverse
health effects, including increase in asthma and respiratory ailments, and heat-wave
related deaths. (Perkins, “Dead Heat: The Health Consequences of Global Warming
Could Be Many,” Science News, July 3, 2004, v.166 n.1 p.10-12)
Enrichment Topic 3. Could Global Warming Start a Little Ice Age in Europe?
Oddly, global warming could bring about a new ice age in Europe. Europe is warmer
than it should be for its latitude. Warm water from the equator travels up North America,
and then the Gulf Stream moves eastward across the Atlantic, then south down the
European coast. The heat stored in these waters warms Europe. Global ocean circulation
is driven by the sinking of cold, dense water in the north Atlantic. If air temperature
warms so much that sea surface temperatures do not cool the North Atlantic waters
sufficiently, they will remain on the surface instead of sinking. This will shut down ocean
circulation, including the Gulf Stream. USA Today (Magazine), June 2002 v.130 n.2685
Enrichment Topic 4. Slight Changes in Climate May Trigger Abrupt Ecosystem
The U.S. Geological Survey assessed the implications that a warming Earth would have
on North American ecological thresholds. An ecological threshold is the point at which
large changes occur that are potentially irreversible. Some of the implications adversely
affect humans, including forest dieback, wildfire, and insect infestations. Humans can
also increase an ecosystem’s potential for reaching the threshold, including water use in
an area that is affected by drought. Although not enough is known about ecological
thresholds, researchers stated that ecosystems will differ significantly. The
Environmental Protection Agency, Synthesis and Assessment Product 4.2: Thesholds of
Climate Change in Ecosystems, http://climatescience.gov
Forest dieback has also been intensely studied. The death rates of trees in US western
forests have doubled over the past 20-30 years. The U.S. Geological Survey attributed the
die-back to higher temperatures as well as water scarcity. The scientists warned that if the
current rate of tree mortality continues, or accelerates, the U.S. forests “could shift from
being a carbon sink that takes greenhouse gases out of the atmosphere to becoming a net
emitter of carbon dioxide.” Eilperin, “Study Ties Tree Deaths to Change in Climate,” The
New York Times, January 23, 2009
12. Pleistocene mineral resources include sand and gravel, placer deposits of gold, and
some evaporite minerals such as borax.
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
Global Warming
1. Discuss the current controversy surrounding global warming. Why has it taken
scientists so long to support the idea of a human cause of a global temperature
increase? Why is it so difficult for scientists to model climate?
2. Discuss the inherent problems when geologists try to decipher human impact on a
climate, when the rock record and other geological data are measured on a much
larger geological time scale. Can scientists effectively measure short-term trends—
such as those that may exist from the start of the Industrial Revolution?
3. The controversy surrounding global warming has been debated on a national and
political level. Why would some businessmen not want to acknowledge global
warming? Who might profit if global warming is a reality? Which countries
produce the most CO2? Do these countries have the greatest population? Is it
morally acceptable for a few individuals to engage in activities that will influence
the entire Earth? This topic offers many opportunities for the integration of cultural,
political, social, and moral views.
4. Investigate how different governments respond to the concept of global warming.
Do third world countries embrace the concept? Do the superpowers embrace the
concept? How have various US administrations responded to requests to
voluntarily reduce the amount of CO2 emissions?
Plate Tectonics Continues
1. While the breakup of Pangaea was a central part of the Earth’s history during the
Mesozoic, it is also important to emphasize to students that the process is
continuing in the Cenozoic. Stress that the Laramide orogeny continued into the
Cenozoic Era, and the mountain-building events that began in the western United
States continue today on the western side of the craton. Have students compare the
amount of time involved in mountain building in the western United States versus
the amount of time involved in mountain building in the Appalachian orogenies.
2. Why is it important that tectonic processes continue on Earth? Have students
hypothesize what would happen if tectonic processes on Earth ceased.
3. What will the future hold for the Earth’s continents if present-day tectonics
continues? Discuss the possible arrangement of Earth’s continents in 1 million
years, 10 million years, and 100 million years. Note how difficult it is to predict
tectonic arrangements in the geologic future.
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
1. Consider the global impact of a new ice age. What would happen to seaports?
Which major cities of the world would be plowed over by ice? How would
agricultural and desert land shift? How would worldwide distribution of
vegetation change?
2. Consider the global impact of continued increased global temperatures. What
would happen to seaports? Which major cities of the world would be submerged?
How would worldwide distribution of vegetation change? How would agricultural
lands be affected? How would animal species that are restricted to certain
environments cope? What are the consequences for humans?
3. How can each one of us make a difference to combat human influence on
continental glacier
end moraine
glacial stage
ice cap
ice-scoured plain
interglacial stage
isostatic rebound
Little Ice Age
Milankovitch theory
pluvial lake
pollen analysis
proglacial lake
U-shaped glacial trough
valley glacier
1. Glaciers, Earth Revealed #23, Annenberg/CPB
2. Living Glaciers, Educational Images, Ltd.
3. Signs of Ancient Ice Sheets, Educational Images, Ltd.
4. A Visit to St. Helens, Educational Images, Ltd.
5. A Geology Field Trip through the Appalachians of Pennsylvania, Educational
Images, Ltd.
6. The Ice World, Discovery Channel
7. The Living Edens, Yellowstone: American’s Sacred Wilderness, PBS Home
8. Mystery of the Megaflood, WGBH Boston
9. Supervolcano, The Discovery Channel
10. Treasured Places in Peril: Global Warming Impacts of the Southeast, Films for
the Humanities and Sciences
11. Can We Save Planet Earth, Open University
12. The Truth About Climate Change, Open University
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
13. Eruption of Mount St. Helens, IMAX
14. Fire Below Us: Remembering Mount St. Helens, National Geographic
15. Glaciers and Icecaps: The Melting, Ambrose Video Publishing
16. Secrets of Glacier National Park, Discovery Communications, Inc.
17. Glaciers, Ambrose Video Publishing
18. Global Warning?, The History Channel
19. Journey to 10,000 B.C., The History Channel
20. Secret Yosemite, National Geographic
21. Secret Yellowstone, National Geographic
22. Ring of Fire, IMAX
23. Global Warming, NOVA
24. Earth in the Time of Climate Change, Classroom Encounters
Slides and Software
1. Ice & Its Effects on the European Landscape, slide set, Educational Images
2. Signs of Ancient Ice Sheets, Educational Images, Ltd.
3. Explore Climate Change CD-ROM, Geological Society of America
Multiple Choice Review Questions
9. d
10. a
Short Answer Essay Review Questions
11. Minor irregularities in Earth’s rotation and orbit are sufficient to alter the amount of
solar radiation that Earth’s receives at any given latitude and can affect climate
changes. When variations in Earth’s orbit and axial tilt combine to decrease net
solar radiation, a glacial onset occurs. Orbital eccentricity, the tilt of the Earth’s
axis, and the precession of the equinoxes all affect the amount of radiation reaching
the Earth.
Continental glaciers result in subdued topography, little or no soil, striated and
polished bedrock exposures and poor surface drainage, characteristic of an icescoured plain. Valley glaciers produce distinctive features such as cirques and
broad U-shaped glacial troughs.
13. The Little Ice Age was a cooling trend, with cooler summers, wetter winters, ice
cap growth, and more extensive and persistent sea ice, which occurred between
1300 and about 1850. Shortened growing seasons caused famine in some northern
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
In Europe and Iceland, glaciers reached their greatest historic extent by the early
1800s, and glaciers in the western United States, Alaska, and Canada also
expanded. Migrations of many Europeans to the New World resulted.
14. A pluvial lake exists during times of glaciation because of the greater precipitation
and overall cooler temperatures, especially during the summer, which results in
lower evaporation rate. Pluvial lakes form far from an area of glaciation. An
example of a pluvial lake was Glacial Lake Missoula.. Proglacial lakes form close
to glaciers, where meltwater accumulates along a glacier’s margin. An example of a
proglacial lake was Lake Bonneville.
15. Any moraine deposited at a glacier’s terminus is an end moraine. As a glacier
advances, it pushes material ahead of it. At its farthest point, it deposits its terminal
moraine. As it melts back, it dumps material, with recessional moraines marking
the places where it was stationary for a while. Therefore a terminal moraine would
mark the farthest point that the glacier traveled, and is also the place where outwash
forms in meltwater streams. Recessional moraines would be closer to the glacier’s
Isostatic rebound occurs when melting of large quantities of ice or erosion reduces
the load on top of the Earth’s crust. Then, the crust slowly rises or rebounds. In
Scandinavia, some coastal cities have rebounded enough so that docks built only
a few centuries ago are now far inland from the shore. In Canada, as much as 100
meters of isostatic rebound has taken place during the last 6000 years. When the
Great Lakes formed, ice sheets covered the land to the north. As the ice sheets
melted, the freed land experienced isostatic rebound.
Lake Missoula formed in Montana when an advancing glacier dammed a valley,
causing water to fill in behind it. When the ice dam failed, the water rushed out at
tremendous velocity and drained south across Idaho and into Washington. In
eastern Washington, the floodwaters stripped the soil and carved huge fluvial
features. This is called the scablands. This history repeated itself several times.
18. Oxygen isotope ratios (O18 to O16) from deep sea cores show the abundance of
glacial ice, because seawater has a higher O18-to-O16 ratio. This is because the
lighter isotope, O16, is more easily evaporated, and during times of glaciation, is
tied up in glacial ice. The declining percentage of O16 and the rise of O18 is
preserved in the shells of planktonic foraminifera, and reveal how the surface water
temperatures were fluctuating. Pollen analysis is used to determine past
environments. When paleontologists identify the type of plant the pollen came
from, they can look at the floral composition of the area and make climatic
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
19. The Cascade Range runs through California, Oregon, Washington, and British
Columbia. In California, basalt lava flows and cinder cones are present. The
volcanoes are still active, as demonstrated by the eruption of Mt. St. Helens in
1980, and recent eruptions of Lassen Peak. (See Chapter 16.) However, there is not
a continuous subduction zone along the western margin. The western margin
includes transform faults as well, and volcanic activity is not common along
transform boundaries.
20. High-resolution stratigraphy is not possible with these deposits. Minor fluctuations
in ice sheet position go unrecorded or unnoticed because glacial tillites are
generally unfossiliferous, unstratified, and difficult to correlate from one locality to
another. Also, the land record is incomplete, as melting and advancing ice sheets
may erase the record of a prior glacial advance.
Apply Your Knowledge
1. It appears that the glacier has a negative budget, or it is experiencing more loss in
volume than gains. The glacier’s terminus will retreat with a negative budget. Also,
the glacier can be moving faster because more meltwater is present that percolates
downward and facilitates basal slip. This would result in the debris moving several
hundred meters toward the glacier’s terminus.
2. From Figure 17.15 in the textbook, we can see that the western area of Nevada was
large covered by Pleistocene lakes. The flat surface, and fine sediments (mud) would
fit in with this scenario. The benches can be explained as terraces, or different
elevations that represent an extended period when the Pleistocene lake stood at that
3. Pleistocene glaciers deposited moraines as they retreated. Although these sediments
were initially deposited by ice, they were modified by wind-generated waves and
longshore currents. The curve of Cap Cod resembles a recurved spit, modified by
longshore currents that moved from the south to the north.
4. The base surface exhibits signs of glaciation. The linear scratches and polish were
probably created by glacial ice moving over the area. The nonstratified mixture of
mud, sand, and gravel indicate deposition by a glacier, since—unlike running water—
glacial ice does not sort. The large gravel—up to 2 m in diameter—also provides
evidence that glacial ice is responsible for the transportation of these sediments.
Neither wind nor ice is powerful enough to move such large sediments. The well
sorted cross-bedded sand indicates a warmer environment, in which deposition
occurred by water. Depending on the size of the cross beds, the sediments may have
been deposited by wind, or fluvial processes. The horizontal layers of conglomerate
also indicate deposition by water. The clasts are rounded (it is a conglomerate as
opposed to a breccia), and the clasts are large, eliminating deposition by wind. These
sediments probably represent an interglacial paleoenvironment.
R.M. Clary, Ph.D., F.G.S..
Department of Geosciences
Mississippi State University
Finally the light and dark clay layers are probably varves, representing an annual
deposit within a lake during a glacial event. The boulders within the varves are
probably drop stones, released from melting ice. Therefore, the area exhibits signs of
glaciation, followed by an interglacial period, and then further glaciation.

CHAPTER 17 - GeoClassroom

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