Download Chapter 15—Cenozoic Events

The Earth Through Time
CHAPTER 15—CENOZOIC EVENTS
CHAPTER OUTLINE FOR TEACHING
I.
Overview of Cenozoic
A. Subdivision of Cenozoic (m.y. = million years)
1. Three periods
a. Paleogene: 65.5 to 23 m.y.
b. Neogene: 23 m.y to 1.8 m.y.
c. Quaternary: 1.8 m.y. to present
2. Epochs of the Paleogene
a. Paleocene: 65.5 to 55.8 m.y.
b. Eocene: 55.8 to 33.9 m.y.
c. Oligocene: 33.9 to 23.0 m.y.
3. Epochs of the Neogene
a. Miocene: 23 to 5.3 m.y.
b. Pliocene: 5.3 to 1.8 m.y.
4. Epochs of the Quaternary
a. Pleistocene: 1.8 to 0.01 m.y.
b. Holocene: 0.01 m.y. to present
B. Plate Tectonics
1. Vast seafloor expansion
a. 50% of seafloor produced during last 65.5 m.y.
b. most new seafloor in Atlantic and Indian Oceans
2. Significant westward movement of N. and S. America
a. San Andreas fault system produced
b. Andean trench deformed
c. Cascade-Panamanian-Andean volcanic chain developed
d. extensive west coast orogensis
3. Significant rifting
a. North Atlantic: Greenland split from Scandinavia
b. South Pacific: Australia split from Antarctica
c. Indian Ocean: Arabia split from Africa (creating Gulf of Aden
and Red Sea)
4. Significant collision events
a. Africa-Eurasia: Alps built
b. India-Eurasia: Himalayas built
5. Cenozoic characteristics
a. continents stood high: transgressions limited
b. sharply defined climatic zones
c. cooling trend culminated in Pleistocene Ice Ages
II. Pre-Pleistocene Cenozoic History
A. Eastern United States
1. Structural changes
a. broad gentle uplifts
b. eastern tilting of Atlantic Coastal Plain and shelf
c. subsiding platforms in Florida-Bahamas area
d. Neogene uplift of Florida
2. Sedimentation and erosion
a. Appalachian plains beveled by erosion
b. valley and ridge topography sculpted
c. coastal plain alluvial sedimentation
d. reworking by marine transgressions
e. coralline carbonates (2500 m) in Florida area
B. Gulf Coast
1.
2.
3.
4.
5.
6.
Best stratigraphic record in N. America
8 major cycles of transgression/regression
Paleocene transgression as far north as Illinois
Common cyclic sequence: deltaic above offshore deposits
Comprise seaward-thickening wedge of clastics
Carbonates absent in region
C. Rocky Mountains and Cordillera
1. Structural changes
a. Late Cretaceous-Paleogene accretion events account for
major structural features of western Cordillera
b. Miocene uplift and erosion exposed present topography (e.g.,
Rocky Mountains)
c. Miocene uplift resulted in re-deposition of Paleogene
sediments of intermountain basins
d. Neogene normal faults elevated the Teton Range (6000 m
displacement): Teton fault scarp is 2500 m high
2. Volcanic activity: widespread in the region
3. Sedimentation
a. Paleocene (e.g., Fort Union Fm., 1800 m thick): clastics in
intermountain basins (silt, sand, shale, coal, lignite)
b. Eocene lake deposits in intermountain basins (e.g., Green River
Fm. in basins between Wind River and Owl Creek Mountains: 600
m of freshwater limestone and shale; seasonal varves; 6.5 m.y record of insect, plant,
and fish fossils; oil shales
c. Eocene stream deposits (e.g., Wasatch Fm.): intermountain basin
fills, red colors; fine upward from conglomerates to siltstones
d. Eocene-Oligocene floodplain deposits (e.g., White River Fm.):
clays, silts, and ash with extensive mammal accumulations in flood deposits
e. Oligocene lacustrine deposits filled with volcanic ash (e.g.,
Florissant beds): spectacular preservation of insects, leaves, fish,
birds, spores, pollen
f. Miocene fluvial and lacustrine sedimentation (intermountain
basins) and piedmont plains (east of Rocky Mountains: grasslands
with camels, horses, rhinoceroses, deer, other grazing
animals; Great Plains developed; spectacular erosional features
g. Pliocene floodplain deposits: reflect cooler, drier conditions
D. Basin and Range Province: Nevada-Utah to Mexico
1. Structural history
a. Mesozoic over-thrusting
b. Paleogene regional arch
c. Miocene-Holocene arch subsidence and normal faulting: northsouth trending fault-block mountains (horsts and grabens)
developed by tensional forces
2. Causes of structural development: four hypotheses
a. subduction hypothesis: Pacific spreading center active below
region as it was subducted
b. oblique shearing hypothesis: tension due to west coast
shearing
3. Sedimentation
a. Miocene evaporites in lakes
b. Miocene-Holocene coarse clastic shed off of mountains
c. Miocene-Holocene clastics fill grabens
4. Volcanism: different styles on different sides of province
a. western side: extensive lava flows
b. eastern side: explosive volcanism (ash and pumice deposits)
E. Colorado Plateau
1. Region of non-folded, flat-lying Paleozoic and Mesozoic rocks
a. crustal buttress with deformation all around it
b. plateau raised repeatedly during Early to Middle Pliocene (5 to
10 m.y. ago)
2. Structure and volcanics: steep faults are avenues for lavas (e.g., in the
San Francisco Mountains, AZ)
3. Uplift and erosion: Grand Canyon cut down 2600 m into crystalline
Precambrian rocks
F. Columbia Plateau and Cascades
1. Region built by two styles of volcanic activity
a. relatively quiet fissure eruptions covering 1/2 million km 2 with
2800 m of lava
b. explosive, violent volcanic mountain chains issuing lava,
pyroclastics, and ash clouds (nuée ardente)
2. Columbia Plateau: Neogene basaltic fissure eruptions; layered basalts
3. Cascade range
a. volcanism due to melting of down-going Juan de Fuca plate
b. volcanism began 4 m.y. ago (Pliocene)
c. recent eruptions: Mt. St. Helens, WA (1980)
d. other recent eruptions: Mt. Lassen (1914-15); Mt. Rainier (2000
years ago)
e. caldera-producing eruption: Mt. Mazama exploded to form
Crater Lake (OR) today
G. Sierra Nevada and western California
1. Sierra Nevada Mountains
a. not supported by thick crust, rather by buoyant liquid rock
b. Jurassic: formed by plutonism in Nevadan orogeny
c. Cretaceous and Cenozoic: eroded deeply
d. Pliocene-Pleistocene: range uplifted 4000 m along huge normal
faults on east side; range tilted west depressing the California
trough on west side
e. Pliocene-Pleistocene: rejuvenated streams and valley glaciers
cut present topography (e.g., Yosemite Park)
2. California west of Sierra Nevada Mountains
a. Paleocene-Miocene: affected by subduction tectonics,
deformation, volcanism
b. Miocene: conversion to strike-slip (transform) fault tectonics;
cease subduction in area
c. Miocene-Pliocene: regression due to uplift
d. Miocene-present: creation of submarine basins due to fault
movements; clastics, cherts, diatomites
e. Holocene: final regression from most western California
marine basin
3. Alaska and arctic islands of Canada
a. Aleutian chain volcanics
b. Aleutian back-arc basin: clastics, pyroclastics, lavas
c. Alaska and Canada: clastics with coal
4. West Coast tectonics
a. East-dipping subduction: Mesozoic and Paleogene
orogenesis
b. Orogenic effects: batholiths, compressional structures,
volcanism, metamorphism, ore emplacement
c. Farallon plate: extensively melted (including spreading ridge);
northern segment = Juan de Fuca plate; southern segment =
Cocos plate
d. Pacific plate: moving northeast prior to west coast contact,
therefore strike-slip fault motion was assumed (Miocene)
e. Baja California split from Mexico: Pliocene (5 m.y. ago);
moving north on Pacific plate
H. South America: Andean orogenic belt
1. Cretaceous: deformation, metamorphism, granitic plutonism
2. Cenozoic (especially Miocene): folding and volcanism
3. Miocene-Pliocene: highlands eroded
4. Late Pliocene: renewed uplift; present-day relief
5. Cenozoic tectonics due to continual subduction of South Pacific
plate under western S. America
6. Cenozoic clastics shed off Andes: Amazon and Orinoco basins
or intermountain rifts
I.
Tethyan Realm (Europe)
1. Eocene deformation
a. Africa moves north toward Eurasia deforming Europe and
creating Pyrenees and Atlas Mountains
b. Northern movement converts to scissor-like closure: beginning
formation of Alps
c. Flysch deposition in basins: dark marine shales, immature
sands, cherts
2. Oligocene deformation
a. enormous recumbent folds form and rise to form mountains from Tethys marine
sediments
b. compression forces folds to north on to Eurasia
c. thrust faults cut folds on undersides
d. molasse deposits: Piedmont clastic wedge shed on north side of
rising Alps
3. Miocene deformation and sedimentation
a. glacial-induced sea-level drop of 50 m
b. tectonic restriction of inlet at straits of Gibraltar
c. factors above isolated the proto-Mediterranean from global sea;
evaporation 5.5 m.y. ago turned basin into an evaporitic basin and
eventually a desert (like Death Valley, CA today)
4. Pliocene-Holocene deformation
a. Jura folds form: older rocks transported over molasse; form
northern front of Alps today
b. Post-Pliocene uplifts continued to today
5. Similar age deformation: Apennines, Caucasus, Carpathians, and
Himalayas
J. Tethyan Realm (India)
1. Paleocene-Oligocene: folding, thrusting, granitic plutonism as ocean
closed between India and Eurasia
2. Miocene: intensive orogenic episode; elongate tracts of seafloor folded
and thrust south onto India; northern trough of India formed (5000 m
continental clastics)
3. Pliocene-Holocene: great elevation of plateaus and folded ranges;
retreat of marginal seas; continued collision of India-Eurasia; Himalaya
Mountains thus built
K. Northern Europe (France, Scotland, Ireland, Spitzbergen, Greenland, Baffin
Island)
1. Early Cenozoic lavas: Giant’s Causeway of Ireland; same age as
Greenland-Europe split
2. Paleocene-Eocene-Oligocene: repeated cyclic transgressions and
regressions into Europe
a. Oligocene: greatest transgression
b. Flooding from North Sea toward SE
c. Paris Basin: thick section above Cretaceous chalks
3. Miocene-Holocene: uplift prevented further transgressions
L. Africa
1. Northern region near Tethys: little deformation, flat-lying rocks
2. Southern region: emergent in Cenozoic
3. Eastern region: Cenozoic uplift and rifting
a. 3000 m of uplift in a broad arch
b. fracturing and normal faulting on arch crest
c. east African rift valleys formed
d. volcanic development in rifts (e.g., Mt. Kenya and Mt.
Kilimanjaro)
e. elongate lakes formed in rifts
M. Antarctica
1. Paleocene-Eocene: Antarctica was joined with Australia and was relatively warm
2. Miocene: Separation from Australia caused warm currents to flow northward and Antarctica
became cold like today
III. Quaternary (Pleistocene and Holocene) History: the last 1.8 m.y.
A. Overview of Epochs
1. Time of ice ages
a. 40 million km3 snow and ice covered 1/3 Earth’s surface
b. glacial terrains created
c. climatic zones shifted southward
d. Arctic conditions in Europe, N. America
e. intensive rain in lower latitudes
f. human evolution and migrations
2. Climatic characteristics
a. glacial and integlacial intervals
b. ocean cooling events independent from glaciation
B. Pleistocene-Holocene Chronology (m.y. = million yrs)
1. Original concept of Pleistocene base (Lyell, 1839)
a. Marine strata young enough to contain 90-100% of presently
living mollusks as fossils
b. Lyell’s concept applied to marine strata in Italy, not worldwide
c. Non-marine record not well defined as a result
2. Modern concept: Pleistocene base = 1.8 m.y. ago
a. 1.8 m.y. widely accepted date of base
b. 1.8 m.y. does not coincide with onset of glaciation; glaciation
not a synchronous event; oldest extensive glaciation = 1.0 m.y.
c. Marine sediments: base is extinction (last occurrence) of
discoasters
d. Continental deposits: base is first occurrence of modern horse
fossils (Equus), elephants, etc.
3. Modern Concept: Holocene base
a. base defined as level (age) of melting of ice sheets to
approximately their present position and sea level rise to near
present level
b. base defined as above = 8000 yr ago
c. some geologists define base as mid-point in glacial retreat and
sea-level rise
d. base defined as above = 11,000-12,000 yr ago
4. Independence from “ice age” concept
a. pre-1975 concept: Pleistocene consisted of 4 glacial intervals
and 3 interglacial intervals; Holocene was final interglacial
interval
b. post-1975 concept: glacial intervals are not synchronous and
more than 4 occurred, therefore epochs independent of such
constraints
c. reasoning for above: discovery of 30 intervals of severe cold
over last 3 m.y.
5. Variables affecting Earth’s climates over time
a. atmospheric changes: greenhouse versus icehouse
b. geographic and tectonic changes
c. oceanographic changes
d. astronomic changes: sunspot cycles, Milankovitch cycles, etc.
C. Terrestrial Stratigraphy of Pleistocene
1. Sedimentary deposits by environment (facies)
a. glacial (till): terminal moraine, ground moraine
b. fluvial (stratified drift): braided and meandering streams
c. lacustrine
2. Erosion surfaces
a. bedrock scour by ice
b. melt-water stream incision
c. melt-water flood (scablands)
3. Correlation and relative-age determination requires mutually sustaining
criteria
a. degree of stream dissection of moraine
b. depth of oxidation of sediment layer
c. degree of chemical weathering of layer
d. fossil pollen as climatic indicators
e. varved clays in lake deposits
f. C14 dating of wood, bone, shell, peat (note: 1/2 life = 5,570 yr)
D. Marine Stratigraphy of Pleistocene: correlation methods in continuous core
1. Oxygen-isotope ratios in calcareous planktonic foraminifers: indicator
of water volume stored as ice in glaciers
a. O18 is heavier and is not evaporated as readily as O16, thus snow
and ice are enriched in O16
b. O18/O16 ratios from cores plotted versus depth in core show
variations in ice volume (thus, sea level) over time; also shows
climate changes
2. Relative abundance of foraminifera sensitive to temperature changes
a. Globorotalia menardii: tropical species associated with warm
waters
b. Globorotalia truncatulinoides: coils right in warm water; coils
left in cold water
c. Background sedimentation rates and ages in core determined by
C14 dating of foraminiferal tests
3. Remnant magnetism
a. depositional remnant magnetism may be correlated with known
geomagnetic time scale
b. age check by allied C14 dating
c. magnetism may be disturbed by bioturbation
E. Effects of Pleistocene Glaciation
1. Sea-level drop: 75 m below today’s level at maximum
a. continental shelves as dry lands (forests, grassland, plains)
inhabited by humans
b. land bridges: British Isles-Europe, Siberia-Alaska
c. interglacial intervals inundated shelves and bridges; forced
animal migrations
2. Glacial physical effects
a. ice-caused erosion
b. weight of ice depressed crust 200-300 m below pre-glacial level;
interglacial crustal rebound (as today); elevation of glacial
coastlines
c. obliteration of river systems by continental glaciers
d. establishment of new glacial and interglacial river drainage
basins (e.g., Missouri and Ohio Rivers)
e. changes in stream gradient and sediment load in glacial versus
interglacial times; sea level affected base levels worldwide
f. continental lakes (e.g., Great Lakes of N. America) scoured in
lowlands by continental ice sheets
g. development of huge ice-dammed lakes of a temporary nature;
huge lake bed deposits exist today (e.g., Lake Agassiz of ND,
MN, and central Canada)
h. pluvial lakes formed: thousands of large and small lakes formed
in low latitudes by excess rainfall in glacial intervals (dry during
interglacials); example: Lake Bonneville, site of salt flats and
Great Salt Lake, UT today
i. glacial impoundment lakes: impoundment floods created
channeled scablands (e.g., draining of Lake Missoula (MT)
resulted in flood of 2000 km 3 water and severe erosion
j. soil erosion: soil stripped off craton of Canada and
transported south
k. loess-blanket deposition: dense, cold air flowing off glaciers
blew fine material from tills and drift to lower latitude areas (e.g.,
loess blankets of Missouri River valley U.S.; central Europe;
northern China)
F. Causes of Pleistocene Climates
1. Any theory must account for reasons whya. climates grew cooler from Middle Cenozoic to Pleistocene
(long-term trend)
b. glacial-interglacial intervals alternate (short term trends)
c. temperature and precipitation conditions mitigate to form
proper combination
d. many factors may be involved
2. Milankovitch theory of solar radiation
a. Earth’s astronomical motion accounts for changes in amount of
solar energy received, thus spawning glacial intervals
b. Earth’s axial tilt: varies 22o to 24o over 41,000 year period
(changes seasonal length-of-day and amount of solar energy at
high latitude)
c. Earth’s axial precession: axis of rotation moves in circle with
period of 26,000 yr
d. Earth’s orbital eccentricity: varies by 2% with a period of
100,000 yr (thus Earth is closer to the sun at times)
e. Support for theory: radiometric and oxygen-isotope studies
show strong correlation to Milankovitch calculations, especially to
role of eccentricity at 100,000 yr intervals over last 600,000 yr
f. Criticism of theory: why not operative over all of geological
time?
3. Other factors affecting Milankovitch climatic change
a. albedo (reflectivity of Earth): currently 33% solar energy
reflected during this interglacial and sea level high stand; during
extreme low sea levels more continent would be exposed and
albedo higher (thus lower global temperatures); 8o C drop per 1% change
b. cloud-ash-dust absorption of solar energy
c. greenhouse gas content (especially CO2); decrease CO2 =
cooling, increase = warming temporarily but cloud cover and
excess precipitation may trigger ice buildup
d. oceanic effects: northward deflection of Gulf Stream-type
currents (e.g., 3.5 m.y. ago when Isthmus of Panama formed)
would send warmth and moisture to northern regions
e. Continental positions: continents must be at or near poles or
snow will fall in ocean and melt
4. Milankovitch predictions of future
a. 20,000 cooling trend going into next glacial
b. unknown factors: CO2 and other atmospheric changes by humans
G. Cenozoic Climates: Global Warming, then Cooling
1. PETM – Paleocene-Eocene Thermal Maximum
a. Global warming from carbon-dioxide buildup in atmosphere
b. Gradual event spanning 10,000 years
c. Melting of sea-floor methane hydrate released methane, which formed carbon dioxide
in the atmosphere
d. Global temperatures rose 8oC during the PETM
e. Disastrous effects
(i) acid rain and acidification of the oceans
(ii) foraminiferal extinction in the oceans
(iii) major shifts of plants and animals on land
2. Oligocene cooling
3. Miocene warming
4. Pleistocene and Holocene cooling and the ice ages
Answers to Discussion Questions
1. (a) Mountains of the Basin and Range were formed during Miocene when the crust under that region
was stretched and such tension caused up-thrown blocks (horsts) to become mountains and downdropped blocks (grabens) to become valleys. (b) The Great Plains was formed during Miocene when
uplift of the Rocky Mountains caused great volumes of clastic sediments to be eroded from the
mountains and deposited eastward. (c) Columbia and Snake River Plateau were formed during
Cenozoic by vast outpouring of basaltic lavas erupted along deep fissures in an area of 500,000 km 2.
(d) The Red Sea was formed during Cenozoic when a branch of the Indian Ocean rift split Arabia
away from Africa and in the process opened this seaway. (e) The Teton Range was formed when
normal faulting accompanying Neogene uplifts affected northwestern Wyoming. (f) The Cascade
Range was formed over the last 4 million years as viscous lavas were intruded into the western
margin of the American plate as a result of subduction of the Juan de Fuca plate of the eastern
Pacific.
2. The Alps, Atlas, Apennines, Carpathians, Caucasus, Pyrennes, and Himalayas are all mountain
ranges formed by the closure of the Tethys seaway.
3. Paleogene Period includes (in order from oldest) Paleocene, Eocene, and Oligocene. Whereas,
Neogene includes Miocene, Pliocene, Pleistocene, and Holocene Epochs.
4. The Green River Formation is economically significant because it contains shales rich in waxy
hydrocarbons, a deposit called oil shale that can be processed to yield petroleum. The Green River
Formation is also the source of crude oil pumped from the adjacent Wasatch Formation. The Fort
Union Formation is economically significant because it contains immense tonnages of low-sulfur coal
in its lower levels.
5. Lake Nyasa and Lake Tanganyika are lakes formed by fault-bounded, down-dropped crustal blocks.
This normal faulting is the result of Cenozoic rifting along a north-south trend in eastern Africa.
6. The Great Salt Lake is part of a much larger, Pleistocene lake called Lake Bonneville which once
covered an area of 50,000 km2 and was as deep as 300 m. Lake Bonneville formed during pluvial or
high-precipitation periods that were the result of glacial stages. Such lakes shrink during drier
interglacial stages like the current stage.
7. Glacial versus interglacial (i.e., cold versus warm) sediment records may be determined by study of
oxygen-isotopic ratios (O18 versus O16) in shells of planktonic marine invertebrates and (or) by
studying changes in relative abundances of foraminifers known to be sensitive to temperature.
8. The Bering land bridge across the Bering Straight was an important connection between Asia and
America. A 50-meter sea-level drop will cause the land bridge to develop. This event likely occurred
occasionally during Cenozoic.
9. Land-level rise around Hudson Bay, the Great Lakes, and Baltic Sea during historic time is the result
of removal of the last glacial ice sheet (which had down-warped the crust owing to its weight) and a
resultant rebound of land elevation.
10. New and faster, Cenozoic westward movement on the American plate and northward movement of
the Pacific plate caused a lateral fault (strike-slip) boundary to develop in the San Andreas fault of
California.
11. Deposition of a seaward-thickening wedge of clastic sediments many 1000s m thick under relatively
shallow-water conditions indicates profound and continual subsidence during Cenozoic.
12. The Green River oil shales contain prolific amounts of hydrocarbons and thus are a rich energy
source. They are located at surface or shallow depth and thus easily
obtained.
Unfortunately, the mining of such deposits deeply scars and affects the land. Hydrocarbons are
tightly bound in the rock and much energy is required to
liberate them. Processing oil shales is
not a clean or efficient operation.
13. Albedo (reflectivity) can be increased by exposing more land surface (as in regression or
deforestation), adding cloud cover or dust/ash content to the atmosphere (as in volcanic eruptions,
great dust storms, or great fires), or adding snow/ice cover. Such changes generally accompany
global climatic change. At the beginning of Pleistocene, sea levels were significantly lowered and
increased snow/ice cover was forming at high latitudes due to oceanic current diversion.
14. Thick Pleistocene loess deposits formed as cold moist winds flowed toward lower latitudes from
continental ice sheets. The winds picked up fine material from glacial surfaces and out-washed drift
and transported it to new sites away from glacial margins. The sediments were originally soils and
pulverized rock entrained by mountain and continental glaciers at higher latitudes. The narrow size
range of loess particles reflects the wind’s narrow size-range capacity for moving particles and
keeping them suspended for significant times in air.
15. O18, being relatively heavy as compared to O16, is preferentially left behind in sea water upon
evaporation. During cool periods the O18 precipitated in snow does not return to the sea, thus the sea
is enriched in heavy O18. The foraminifers taking oxygen to build their carbonate (CaCO 3) tests do
not discriminate between isotopes; therefore their tests are enriched in O 18 during cool intervals.
16. Methane hydrates are cold, sea-floor deposits of methane gas (CH4) that is dissolved in or trapped in
water ice. As methane hydrates melt due to volcanic activity on the sea floor or global warming
effects, the released methane gas breaks down and the carbon in the methane combines with oxygen
in the atmosphere to make carbon-dioxide, a greenhouse gas.
17. d
18. a
19. d
20. c
Chapter Activities
Student activities for in-depth learning.
1. Using the resources on this page about the Channel Scablands (http://www.uwsp.edu/geo/
projects/geoweb/participants/dutch/vtrips/Scablands0.HTM), describe how these unusual Pleistocene
features formed and their relationship to glacial ice melting. What is the relationship of the scablands
deposits to the Columbia Plateau?
2. Use the web resources of the University of California, Berkeley, Museum of Paleontology web page on
the Green River Formation (http://www.ucmp.berkeley.edu/tertiary/eoc/greenriver.html) to learn about
how that formation was deposited and the types of fossils found there. Describe these fossils and the
environment of the lake during Eocene.
CHAPTER 15—CENOZOIC EVENTS
CHAPTER OVERVIEW
The era we call Cenozoic is divided into three periods: Paleogene; Neogene; and Quaternary. The
Cenozoic, although covering only the last 65 million years of Earth’s history, encompasses major
worldwide changes. One such change occurred when the North Atlantic rift extended to the north,
separating Greenland from Scandinavia and thereby destroying the land connection between Europe and
North America. During late Eocene, Australia separated from Antarctica and then began its journey to its
present location. This is considered the only major continental breakup during Cenozoic; however, it
appears to have affected climates around the world.
The stratigraphy of the Cenozoic of North America is explored with some of the more noteworthy
exposures: the Gulf Coast, Rocky Mountains, High Plains, Basin and Range, Colorado Plateau, Columbia
Plateau and Cascades, Sierra Nevada, and California are discussed. Cenozoic sedimentation and
deformation outside North America is also discussed in order to complete this phase of Cenozoic history.
Pleistocene glaciation is a focal point in this chapter which highlights the glacial and interglacial stages in
North America and Europe as well as discussing variations in climatic conditions.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:






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
Sketch and label the three periods - Paleogene, Neogene, and Quaternary - and the epochs
within each.
Discuss the tectonic-climate connection.
Locate on a map the major mountain systems that were formed by the northward moving
African block as it collided with the southern margin of Europe.
Explain the origin of the following physiographic features of North America – Rocky
Mountains/High Plains, Basin and Range, Colorado Plateau, Columbia Plateau and
Cascades, Sierra Nevada, and California.
Describe the origin of the San Andreas Fault.
Explain the orogenic events along the Tethys seaway and the orogenic events that led to the
formation of the Alps, Carpathian, Pyrenees, Apennines, and Himalayas.
Discuss the origin of Lake Molawi and Lake Tanganyika in eastern Africa.
List the four Glacial/Interglacial Stages for North America and Europe from oldest to


youngest.
Discuss the impacts of Pleistocene glaciation.
Explain the Milakovich effect (theory) and its possible interpretation of the Pleistocene
glaciation including the three variables in your explanation.
CHAPTER OUTLINE
I.
The Tectonics-Climate Connection
II.
Stability and Erosion Along the North American Margin
III.
Gulf Coast: Transgressing and Regressing Sea
IV.
The Mighty Cordillera
A. Sediment and Mineral Wealth
B. Remarkable Fossils
C. Majestic Scenery
V.
Creating the Basin and Range Province
VI.
Colorado Plateau Uplift
VII.
Columbia Plateau and Cascades Volcanism
VIII.
Sierra Nevada and California
IX.
The New West Coast Tectonics
X.
Meanwhile, Drama Overseas …
A. Northern Europe
B. Rifting Africa
C. Semitropical Antarctica
XI.
Big Freeze: the Pleistocene Ice Age
A. Pleistocene and Holocene Chronology
B. Stratigraphy of Terrestrial Pleistocene Deposits
C. Pleistocene Deep-Sea Sediments
D. Many Impacts of Pleistocene Glaciation
1. Shifting Sea Level
2. Depressed Crust Rebounds
3. Redirecting Mighty Rivers
4. Forming Lakes, Great and Small
5. Washington’s Alien Land: the Channeled Scablands
6. Windblown Sediment
XII.
What Caused the Ice Age?
A. Milankovitch Cycles
B. Earth’s Albedo
C. Other Factors
XIII.
Cenozoic Climates: Global Warming then Cooling
KEY TERMS (pages given in parentheses)
albedo (500):
albedo.
The fraction of solar energy reflected back into space is termed the Earth’s
channeled scablands (497): With the recession of the glacier, the ice dam broke, and
tremendous floods of water rushed out catastrophically across eastern Washington, causing
severe erosion and depositing huge volumes of gravel, boulders, and cobbles. The dissected
region is appropriately termed the channeled scablands. This event was associated with the
formation of Pleistocene lakes in the northwestern corner of the United States.
discoasters (493): Calcareous, often star-shaped fossils believed to have been produced by
golden-brown algae related to coccoliths.
kettle (496): A depression in glacial drift that is formed by the melting of a detached block of ice
that was buried in the drift.
little ice age (493): The four-century period (AD 1540 and 1890) when temperatures were often
1.5° C cooler than today in Europe and the United States.
loess (497): Deposits of thick layers of windblown silt formed from fine-grained glacial sediments
that have been spread across outwash plains and floodplains by wind transportation.
Neogene (470): The middle period during Cenozoic that encompasses two ages, Miocene and
Pliocene. Neogene is followed by the latter period of Cenozoic, called Quaternary, which is
comprised of Pleistocene and Holocene.
oil shale (476): A dark-colored shale rich in organic material that can be heated to liberate
gaseous hydrocarbons.
Paleogene (470): The initial period of Cenozoic that encompasses three ages, Paleocene,
Eocene, and Oligocene.
Pleistocene Ice Age (491): About one-third of the Earth’s land surface became buried beneath
more than 40 million cubic kilometers of snow and ice.
pluvial lakes (496): A lake formed in an earlier climate when rainfall was greater than at present.
precession (499): The way the axis of rotation moves slowly in a circle that is completed every
26,000 years.
stratified drift (494): Deposits of glacial clastics that have been sorted and stratified by the
action of meltwater.
Tethys sea (488): A great east-west trending sea which laid between Laurasia and Gondwonland
during the Paleozoic and Mesozoic from which arose the Alpine-Himalayan mountain range.
till (494): Unconsolidated, unsorted, unstratified glacial debris.
varves (475): Seasonal layers of dark and light sediment formed in glacier-related lakes.
1
THE EARTH THROUGH TIME
TENTH EDITION
H A R O L D L. L E V I N
CHAPTER 15
Cenozoic Events
2
THE CENOZOIC ERA
3
ny other organisms
Paleozoic and Mesozoic.
ion of humans
THE CENOZOIC ERA
4
PERIODS OF CENOZOIC
see these terms
on older maps and in older publications.
and Quaternary. The two new periods of the Cenozoic are now internationally recognized as
Paleogene and Neogene.
5
PALEOGENE PERIOD
Paleogene is divided into three epochs:
6
NEOGENE PERIOD
Neogene is divided into four epochs:
7
QUATERNARY PERIOD
Quaternary is divided into two epochs:
8
NAMING THE EPOCHS
fossil marine invertebrates, found in rocks of that time, that are still living.
example, only 3% of Eocene organisms found as fossils are still living, whereas 17% of
Miocene organisms found as fossils are still alive, and 50-67% of Pliocene fossils are still living.
9
NAMING THE EPOCHS
The meanings of the root words for the epochs refer to the proportions of fossil species that are
still alive.
Pleist = most
Pleion = more
Meion = less
Oligos = few
Eos = dawn
Paleo = ancient
10
PALEOGEOGRAPHY AND PLATE TECTONICS
ents moved to their
current positions.
-ocean ridges since the beginning of
Cenozoic.
11
Position of the continents
during Eocene, about 50 m.y. ago.
Yellow = areas of major
tectonic changes.
PALEOGEOGRAPHY AND PLATE TECTONICS
(J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.)
12
Position of the continents today .
Yellow = areas of major tectonic changes.
PALEOGEOGRAPHY AND PLATE TECTONICS
(J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.)
13
EOCENE VS. TODAY
Yellow = areas of major tectonic changes.
PALEOGEOGRAPHY AND PLATE TECTONICS
(J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.)
14
EXOTIC TERRANES
As the North American plate moved westward (accompanying the widening of the Atlantic
Ocean), subduction of ocean crust and accretion of exotic terranes occurred along its western
edge.
15
moving Pacific Plate, forming the San Andreas Fault system.
SAN ANDREAS FAULT SYSTEM
16
CLOSURE OF THE TETHYS SEA
he Alps and Himalayas.
17
TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE
American plates.
This caused the formation of the Isthmus of Panama, a land bridge linking North and South
America.
18
TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE
was deflected to the north (turning to the right, as a result of the Coriolis Effect), and formed the
Gulf Stream.
hward and resulted in bringing warmer climates to
northwestern Europe.
in precipitation which helped build the glacial ice sheets.
19
IMPORTANT CONTINENTAL BREAKUPS:
1.North Atlantic rift separated Greenland from Scandinavia
2.Australia separated from Antarctica. Circumpolar currents isolated Antarctica from warmer
waters. Led to cooling of Antarctica.
3.Cold, dense ocean waters around Antarctica drifted northward along ocean floor, contributing to
global cooling and the Ice Age.
4.Rifting occurred between Africa and Arabia, forming the Red Sea and the Gulf of Aden.
20
TECTONIC AND PALEOGRAPHIC CHANGES AND THEIR EFFECTS ON CLIMATE
nts retreated toward the equator.
21
PALEOGENE PERIOD
Paleogene was dominated by:
FIGURE 15-7
22
EASTERN AND SOUTHEASTERN NORTH AMERICA
proceeded, gentle isostatic uplift occurred. This stimulated more erosion, as streams cut
downward.
23
EASTERN AND SOUTHEASTERN NORTH AMERICA
Uplift in the eroding Appalachians was coupled with downward tilting and deposition of sediments
on the Atlantic Coastal Plain and continental shelf.
Sediments thicken seaward forming a clastic wedge.
24
EASTERN AND SOUTHEASTERN NORTH AMERICA
sediments accumulated in Florida where less terrigenous clastic sediment was
available.
Atlantic and Gulf Coastal Plains.
ght Gulf of Mexico waters inland as far as
southern Illinois.
25
EASTERN AND SOUTHEASTERN NORTH AMERICA
region. These sediments provided ideal conditions for formation and entrapment of oil and gas.
Much of the oil was trapped around salt domes.
sediments are >10,000 m (>5.5 mi) thick.
ing rapidly.
26
ROCKY MOUNTAINS AND HIGH PLAINS
deformation.
intermontane basins.
Pliocene sands, shales, and lignites were deposited on western high plains.
27
ROCKY MOUNTAINS AND HIGH PLAINS
ediments, indicating volcanic activity, and
providing radiometric dates for correlation.
shales, lignites, and low sulfur coals, deposited in swamps in the intermontane basins.
low sulfur content.
28
ROCKY MOUNTAINS AND HIGH PLAINS
laminated oil shale, and limestone.
The Green River fish, Diplomystis
The Green River Formation, Utah
29
ROCKY MOUNTAINS AND HIGH PLAINS
well-preserved skeletons of Oligocene mammals. Also makes
up the Badlands of South Dakota.
in Colorado. They were buried when Oligocene volcanic ash settled into a lake. Large petrified
stumps of sequoia trees are also present.
Harold Levin
30
ROCKY MOUNTAINS AND HIGH PLAINS
the Miocene epoch.
y Miocene time.
horses, rhinos, deer, and other grazing mammals.
31
ROCKY MOUNTAINS AND HIGH PLAINS
n Rockies.
32
ROCKY MOUNTAINS AND HIGH PLAINS
scenery.
33
BASIN AND RANGE PROVINCE
in Nevada and western Utah, extending
southward into Mexico.
-faulted mountain ranges and down-faulted basins.
34
THE BASIN AND RANGE FORMED AS FOLLOWS:
1.The region was up-arched during Mesozoic.
2.Subsidence occurred along normal faults beginning during Miocene.
3.Up-faulted crustal blocks formed linear mountains that shed sediment into the adjacent downdropped basins.
4.Faults opened conduits for igneous rock, producing lava flows and volcanism.
35
5.Erosion followed the volcanism. Sediments eroded from the mountains filled the down-faulted
basins, clogged rivers, and caused closed-basin (no outlet) lakes to form.
6.Evaporite minerals (gypsum and salt) were deposited as the lakes evaporated.
THE BASIN AND RANGE FORMED AS FOLLOWS:
36
COLORADO PLATEAU UPLIFT
The best-known feature in the Colorado Plateau is the Grand Canyon.
Eroded by the Colorado River to a depth of more than 1.6 miles.
The river eroded through Phanerozoic strata and into the Precambrian basement rocks.
Harold Levin
37
COLORADO PLATEAU UPLIFT
-lying. They were not deformed during Mesozoic orogenies.
providing conduits for volcanic rocks.
38
COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM
volcanic activity.
Washington, Oregon, and parts of Idaho during Miocene, about 15 m.y. ago.
ons on Earth.
39
COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM
Above: Columbia Plateau basalts in a canyon of the Snake River. Right: Mt. St. Helens,
Washington, prior to eruption and during eruption (1980).
40
COLUMBIA PLATEAU AND CASCADE RANGE VOLCANISM
Range.
eastern Pacific.
FIGURE 15-23 The small Juan de Fuca plate plunges beneath Oregon and Washington.
41
VOLCANOES OF THE CASCADE RANGE
42
CRATER LAKE
Crater Lake, Oregon formed from the eruption and collapse of Mt. Mazama in the Cascade
Range about 6800 years ago.
43
The Sierra Nevada batholith formed as the Farallon plate was being subducted under the western
edge of the North American continental plate during Mesozoic.
SIERRA NEVADA BATHOLITH
44
SIERRA NEVADA MOUNTAINS
Erosion during Paleogene removed the overlying rocks and caused the granite batholith to be
exposed at the surface.
45
SIERRA NEVADA MOUNTAINS
to a height of 4000 m (more than 2 miles) above the California trough to the west.
– Yosemite, Lake Tahoe
46
CALIFORNIA
Miocene, strike-slip movement replaced subduction.
47
NEW WEST COAST TECTONICS
cific rise spreading center was subducted under North America.
48
NEW WEST COAST TECTONICS
movement changed.
rally along the edge of the North American
plate.
-slip motion, and ended subduction in this area.
49
AROUND THE WORLD
–New Mexico, Arizona, Idaho
–Mexico
–Iceland
–Pacific rim
–Tetons of Wyoming
–Sierra Nevada
–central and northern Rockies
–Alps
–Himalayas
50
EOCENE VS. TODAY
Yellow = areas of major tectonic changes.
(J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.)
51
Basaltic lava flows in northern Europe and neighboring areas that resulted from Greenland rifting
from Europe
- columnar basalts of Giant's Causeway
CLOSING OF TETHYS SEA AND FORMATION OF MOUNTAIN RANGES
52
Paris" gypsum deposits during Paleogene (Eocene to Oligocene)
and volcanoes
EUROPE, AFRICA, AUSTRALIA, AND ANTARCTICA
53
CENOZOIC PALEOCLIMATES
54
GLOBAL SURFACE COOLING
end of Cretaceous Period.
nd.
-20o closer to the poles than at present.
55
ANTARCTICA DURING PALEOGENE
spores and pollen, despite the fact that it sat on the South Pole.
more equatorial latitudes.
56
nts developed around Antarctica, cutting it off from equatorial
currents.
Yellow = areas of major tectonic changes.
ANTARCTICA DURING PALEOGENE
(J. C. Brider, G. E. Dreway, and M. G. Smith, 1974, Jour. Geol., 82:556–558.)
57
GLOBAL SURFACE COOLING
-13o C (roughly 22o F) near the Eocene-Oligocene boundary,
as indicated by isotope data from brachiopods from New Zealand.
orm by 38 m.y. ago.
58
WORLDWIDE COOLING RESULTED IN:
1.First Cenozoic widespread growth of glaciers in Antarctica about 38-22 m.y. ago.
2.Global sea level dropped by about 50 m during early Oligocene, as glaciers formed.
3.Cold, dense polar water flowed northward across ocean bottom.
4.Upwelling of cold bottom waters affected world climate.
59
5.Decrease in diversity and extinctions of many:
ifera
6.Extinctions were earlier and more severe at higher latitudes.
7.Reefs shifted toward the equator.
8.Calcarous biogenic deep sea sediments (foraminiferal ooze) shifted toward the equator and
were replaced by siliceous biogenic sediments (diatom and/or radiolarian ooze) at higher
latitudes.
WORLDWIDE COOLING RESULTED IN:
60
9.Changes in pollen indicate long term cooling and drying.
ed to tropical, equatorial areas.
10.Glaciation occurred in other areas in Pliocene (and younger) deposits - Sierra Nevada,
Iceland, South America, and Russia.
WORLDWIDE COOLING RESULTED IN:
61
MEDITERRANEAN EVAPORITE DEPOSITS
with glaciation during Miocene, resulted in the isolation of the
Mediterranean basin.
-2000 m) evaporite deposits (gypsum,
halite), 5-6 m.y. ago.
62
ANTARCTIC ICE
t Miocene (about 5 m.y. ago), ice volume in Antarctica was greater than today.
63
ANTARCTIC BOTTOM WATERS
(Cold water is denser than warmer water.)
ocean-floor waters moved downward and outward, away from Antarctica.
Eocene and early Oligocene, and ultimately led to the Pleistocene Ice Age.
64
PLEISTOCENE
cene began 1.8 m.y. ago.
-Holocene boundary is placed between about 12,000 and 11,000 years ago, at
the midpoint of the warming of the oceans.
65
PLEISTOCENE ICE AGE
land area.
Alps, and other mountain ranges of Europe.
66
AS A RESULT OF THE ICE AGE:
1.Climatic zones in the Northern Hemisphere were shifted southward.
2.Arctic conditions prevailed across Europe and the U.S.
3.Sea level dropped as much as 75 m (225 ft) and the shoreline shifted seaward, exposing the
continental shelves as dry land.
4.Streams cut deep canyons into the continental shelves and on land.
67
5.Land bridges existed and led to migrations of mammals, including humans
6.The land was sculpted by glaciers in Europe and North America.
7.U-shaped valleys formed in mountainous areas
AS A RESULT OF THE ICE AGE:
68
8.Rainfall increased at lower latitudes.
9.Large lakes formed in the Basin and Range Province.
AS A RESULT OF THE ICE AGE:
69
10.Winds coming off glaciers blew sediment southward forming löess deposits (Missouri River
area, central Europe, northern China)
11.Parts of northern and eastern Africa that are currently arid had abundant water and were fertile
and populated by nomadic tribes.
12.Nomadic tribes hunted along the edges of the continental glaciers. Wild game was abundant,
furs provided warm clothing, and there were less problems with spoiled meat in the cold
temperatures.
AS A RESULT OF THE ICE AGE:
70
13.Formation of the Great Lakes (depressions scoured by glaciers and flanked by moraines)
14.Formation of Cape Cod, MA - a moraine
15.Formation of Long Island, NY - a terminal moraine
16.Formation of Niagara Falls
17.Formation of large ice-dammed lakes, including Lake Missoula which drained catastrophically,
forming the channeled scablands
18.Formation of hummocky topography and Pleistocene sand dunes
AS A RESULT OF THE ICE AGE:
71
19.Weight of the ice depressed the continental crust to as much as 200-300 m downward.
20.Uplift (isostatic rebound) after ice melted. Coastal features are now elevated high above sea
level.
Map illustrating post-glacial uplift in North America.
AS A RESULT OF THE ICE AGE:
FIGURE 15-43
72
ADVANCE OF THE ICE SHEETS
had strong, rapid, climatic fluctuations.
-1970's, Pleistocene was divided into four glacial stages with intervening warmer
interglacial stages.
ore recent investigations have shown that there may have been as many as 30 glacial
advances over the past 3 million years (roughly every 100,000 years.)
73
NAMES OF THE "TRADITIONAL" GLACIAL AND INTERGLACIAL STAGES IN NORTH
AMERICA
74
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
Pleistocene deposits are difficult to date and correlate.
Pleistocene sedimentary deposits, however, may show evidence of fluctuating climatic conditions,
which can be used to mark times of glacial advance and retreat.
75
1.Evidence of Glacial Conditions
- unsorted mixture of clay to boulder-sized particles. Amount of weathering of glacial
deposits or soils, and the amount of dissection by streams may help with relative dating.
rift - glacial deposits which have been washed and sorted by meltwater
- seasonal laminations deposited in glacial lakes. Counting varves may reveal the
number of years during which they clay was deposited.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
76
2.Plant Remains
- types of plants indicate climate
= COOL climate
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
77
3.Radiometric dating of wood, bone, or peat using carbon-14.
-life of carbon-14 (5730 yrs).
4.Magnetic stratigraphy
The record of magnetic reversals in cores of deep sea sediments can be correlated to magnetic
reversals in volcanic rocks.
same magnetic characteristics.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
78
5.Correlation of deep-sea sediments from cores, using fossil remains, particularly microfossils
such as foraminifera. Fossils can be dated by relating them to paleomagnetic data and to
radiometric dates.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
79
6.Oxygen Isotope Ratios
-18 to O-16 in foram shells from cores tells us the volume of water stored in glacial
ice.
atom.
-16 has 8 neutrons, and
xygen-18 has 10 neutrons.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
80
6.(cont.) Oxygen Isotope Ratios
that make up the shells of forams.
-18 to O-16 in the water (and in shells) depends on temperature.
-16) accumulate in glacial ice. Why? During evaporation, lighter
isotopes are concentrated in the water vapor in the air. Water with lighter oxygen (O-16) is easier
to evaporate than water with heavier oxygen (O-18).
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
81
6.(cont.) Oxygen Isotope Ratios
result, O-16 becomes trapped in glacial ice.
-18 remains in the oceans, because water with O-18 did not evaporate as readily.
r becomes drier, and the percentage of O-18 in seawater (and in foram
shells) increases.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
82
6.(cont.) Oxygen Isotope Ratios
-16/18 signal:
-18 = COLD & DRY, or glacial conditions.
-16 = WARM & WET, or interglacial conditions.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
83
Graph representing variations in the oxygen isotope ratios in foram shells (and in the global
volume of ice) over the past 500,000 years.
6.(cont.) Oxygen Isotope Ratios
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
84
7.The type of foraminifera fossil present may indicate something about the paleoclimate.
Some species live in warmer water. If those species are absent, it may indicate that the water
was colder due to a glaciation.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
85
8.Coiling directions in foraminifera shells
One particular species of foraminifera, Globorotalia truncatulinoides, is known to coil:
left in colder waters.
By examining the percentage of right- and left-coiled specimens, a cyclic pattern representing
glacial advances and retreats can be determined.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
86
Graphs illustrating the percentages of right-coiling and left-coiling foraminifera, Globorotalia
truncatulinoides.
The vertical scale is depth in deep sea sediment cores, in centimeters.
STRATIGRAPHY OF PLEISTOCENE DEPOSITS
87
WHY DID EARTH'S SURFACE COOL?
There was both a long-term decline in temperatures, as well as an oscillation of glacial and
interglacial stages.
Any hypothesis for the cooling must consider both of these factors.
88
MILANKOVITCH CYCLES
oscillations.
referred to as the Milankovitch cycles.
89
MILANKOVITCH CYCLES
relationships
between the Earth and Sun due to periodic fluctuations in Earth's orbit.
- Earth's axis wobbles or moves in a circle like a spinning top over 26,000 years,
affecting the amount of solar radiation received at the poles.
90
MILANKOVITCH CYCLES
2.Orbital eccentricity - Earth's orbit around the Sun changes from more circular to more elliptical
by about 2% over about 100,000 years, moving the Earth closer to or farther from the Sun, and
varying the amount of solar radiation received by the Earth.
91
MILANKOVITCH CYCLES
3.Angle of tilt of Earth's axis - currently about 23.5o, this tilt angle causes the seasons.
Tilt angle varies from about 21.5o - 24.5o over about 41,000 years, changing length of days and
amount of solar radiation received at the poles.
92
MILANKOVITCH CYCLES
radiation received by the Earth, which causes cycles of cooling and periodic glaciations.
well to glaciation episodes, which have occurred every 100,000
years over the past 600,000 years, as indicated by oxygen isotope data.
93
1.Albedo or reflectivity of the Earth
If Earth's albedo increased, due to snow cover, cloud cover, or dust in the atmosphere, the
atmospheric temperatures would decrease due to reflection of solar radiation into space.
As snow cover increased, albedo would increase, producing a positive feedback relationship,
accelerating the rate of glacial growth. A 1% loss of incoming solar energy would result in a
temperature drop of about 8o C, which might be sufficient to trigger glacial buildup.
NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE
94
2.A decrease in atmospheric CO2 would cause a decrease in the greenhouse effect, and lead to
cooling.
3.Conversely, an increase in atmospheric CO2 would cause warming, which would result in more
rapid evaporation, more cloud cover, and an increase in albedo, which could trigger glaciation.
NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE
95
4.Plate tectonics is important in that a continent must lie on or near a pole for snow to build up to
form a glacier.
5.Plate tectonics is further involved because the formation of the Isthmus of Panama diverted the
Gulf Stream northward about 3.5 million years ago. The warm, moist air associated with this
ocean current led to an increase in snowfall in northern areas and the development of continental
glaciers.
NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE
96
6.The impact of human activities, such as increased burning of fossil fuels and the associated
buildup of greenhouse, is having and will continue to have an effect.
NON-MILANKOVITCH FACTORS IN GLOBAL CLIMATE CHANGE
97
THE "LITTLE ICE AGE"
– 1890. Temperatures were several degrees cooler than
today.
pot activity from 1645 -1715 is known as the Maunder Minimum.
98
THE "LITTLE ICE AGE" – CONT’D
incoming solar radiation.
Summer."
Europe.
99
END OF THE "LITTLE ICE AGE"
-induced warming may be the reason for the end of the "Little Ice Age."
global warming and climate change today.
100
• FIGURE 15-7 Generalized paleogeographic map of North America during the Paleogene.
Source:
• FIGURE 15-23 The small Juan de Fuca plate plunges beneath Oregon and Washington.
Source:
• FIGURE 15-43 Postglacial uplift (rebound). Source:
IMAGE CREDITS
101