Historical Geology
INTRODUCTION
CENOZOIC PLATE TECTONICS—AN OVERVIEW
CENOZOIC OROGENIC BELTS
Alpine-Himalayan Orogenic Belt
Circum-Pacific Orogenic Belt
NORTH AMERICAN CORDILLERA
Laramide Orogeny
Cordilleran Igneous Activity
Basin and Range Province
Colorado Plateau
Rio Grande Rift
Pacific Coast
THE CONTINENTAL INTERIOR
CENOZOIC HISTORY OF THE APPALACHIAN MOUNTAINS
¨ Perspective The Great Plains
NORTH AMERICA’S SOUTHERN AND EASTERN CONTINENTAL MARGINS
Gulf Coastal Plain
Atlantic Continental Margin
PALEOGENE AND NEOGENE MINERAL RESOURCES
The following content objectives are presented in Chapter 16:
¨ Geologists divide the 66-million-year-long Cenozoic Era is into two periods, the Paleogene and the Neogene, each of which consists of several epochs.
¨ The breakup of Pangaea began during the Triassic Period and continues to the present, giving rise to the present distribution of land and sea.
¨ Cenozoic orogenies were concentrated in two belts, one that nearly encircles the Pacific Ocean basin, and another that trends east-west through the Mediterranean basin and on into southeast Asia.
¨ The Late Cretaceous to Eocene Laramide orogeny resulted in deformation of a large area in the west, called the North American Cordillera, which extends from Alaska to Mexico.
¨ Following the Laramide orogeny, the North American Cordillera continued to evolve as it experienced volcanism, uplift of broad plateaus, large-scale block faulting, and deep erosion.
¨ The Great Plains consist of huge quantities of sediments that were eroded from the Rocky Mountains and transported eastward.
¨ A subduction zone was present along the western margin of the North American plate until the plate collided with a spreading ridge, producing the San Andreas and Queen Charlotte transform faults.
¨ An epeiric sea briefly occupied North America’s continental interior during the Paleogene.
¨ Thick deposits of sediment accumulated along the Gulf and Atlantic Coastal plains.
¨ Renewed uplift and erosion account for the present-day Appalachian Mountains.
¨ Paleogene and Neogene rocks contain mineral resources such as oil, oil shale, coal, phosphorus, and gold.
To exhibit
mastery of this chapter, students should be able to demonstrate comprehension
of the following:
¨ the continuation of Pangaea’s breakup
¨ the nature of orogenic activity and plate tectonic setting of the major orogenic belts
¨ the Laramide orogeny as a continuation of the Mesozoic Cordilleran orogenic activity
¨ the differences between the Laramide orogeny and the earlier Cordilleran orogenic episodes
¨ the erosion of Laramide uplifts and deposition in the Interior Lowlands
¨ the nature of sedimentation and intrusion of salt domes on the Gulf Coastal Plain
¨ the Cenozoic evolution of the Appalachians and the Atlantic Coastal Plain
¨ the major types and origins of Cenozoic ore deposits
1. The Late Triassic rifting of Pangaea continued through the Cenozoic and accounts for the present distribution of continents and oceans.
Figure 16.1 Geologic Time Scale for the Cenozoic Era
Figure
16.2 Cenozoic Sedimentation and
Volcanic Rocks in the Western United
States
Figure
16.3 Paleogeography of the World
During the Cenozoic
Enrichment Topic 1. The
Future of the Quaternary
Although the Quaternary Period was an important term in geological vernacular for decades, the Geological Time Scale 2004 of the International Commision for Stratigraphy (ICS) removed the Quaternary as a formal unit. The unit formerly known as the Quaternary was subsumed into the Neogene Period, although the epochs of the former Quaternary, the Pleistocene and the Holocene, remained. It seems that the Quaternary had never been formally defined, and in terms of its length, the Quaternary was an anomaly as the shortest period. Also, the Quaternary and the Pleistocene were nearly synonymous. However, not all geologists have embraced the new division: The Journal of Quaternary Science continues to be published. “The Future of the Quaternary,” Geoscientist, 2006 v.16 n.7 p.28-29.
2. Cenozoic orogenic activity was concentrated mostly in two major belts: the Alpine-Himalayan orogenic belt and the circum-Pacific orogenic belt. Each belt is composed of smaller units called orogens.
Figure 16.4 Earth’s Present-Day Orogenic Belts
3. The Alpine orogeny resulted from convergence of the African and Eurasian plates. Mountain building took place in southern Europe, the Middle East, and North Africa. Plate motions also caused the closure of the Mediterranean basin, which became a site of evaporite deposition.
Figure 16.5 The Alps in Europe are Part of the
Alpine-Himalayan Orogenic
Belt
4. India separated from Gondwana, moved north, and eventually collided with Asia, causing deformation and uplift of the Himalayas.
Figure 16.6 Plate Tectonics and the Himalayan Orogen
5. Orogens characterized by subduction of oceanic lithosphere and volcanism took place in the western and northern Pacific basin. Back-arc spreading produced back-arc marginal basins such as the Sea of Japan.
Figure 16.7 Back-arc Spreading and the Sea of Japan
6. Subduction of oceanic lithosphere occurred along the western margins of the Americas during much of the Cenozoic.
Figure 16.8 The Andes Mountains in South America
7. Subduction continues beneath Central and South America, but the North American plate is now bounded mostly by transform faults, except in the Pacific Northwest.
8. The North American Cordillera is a complex mountainous region extending from Alaska into Mexico. Its Cenozoic evolution included deformation during the Laramide orogeny, extensional tectonics that formed the Basin-and-Range structures, intrusive and extrusive volcanism, and uplift and erosion.
Figure 16.9 The North American Cordillera and the Major Provinces in the
United States and Canada
9. Shallow angle subduction of the Farallon plate beneath North America resulted in the vertical uplifts of the Laramide orogeny. The Laramide orogen is centered in the middle and southern Rockies, but deformation also took place far to the north and south.
Figure 16.10 Laramide Orogeny
Figure 16.11 Laramide Deformation in the Northern Rocky Mountains
10. Cordilleran volcanism was more or less continuous through the Cenozoic. The Columbia River basalts represent one of the world's greatest eruptive events. Volcanism continues in the Cascade Range of the Pacific Northwest.
Figure 16.12 Cenozoic Volcanism
Figure 16.13 Cenozoic Volcanism in California and Oregon
Figure 16.14 Cascade Range Volcanism
Beneath the Pacific Northwest, the Juan de Fuca plate is subducting beneath North America. Above it lays a volcanic arc, the Cascade Range. Its most famous member, Washington’s Mount St. Helens, exploded in 1980 and killed 57 people. But the eruption of St. Helens was not a large one; the mountain’s 1480 eruption was five times larger. Mount Rainier, also in Washington, doesn’t tend to explode; it is prone to large mudflows and some nearby towns are built on old ones. Large mudflows have extended to the Seattle and Tacoma areas in the past. Mount Shasta in northern California is even more dangerous, but it is not near any large population centers. Although these mountains could kill a lot of people and do a lot of damage, earthquakes may represent an even greater danger. While the Pacific Northwest is not known for its earthquakes, many appear in the geological record. The last earthquake was about 300 years ago, when it is likely that the entire subduction zone ruptured at once, resulting in a quake that seismologists say would have measured approximately 9 on the Richter scale. While 700 years passed between that quake and the previous one, the two previous earthquakes had intervals of only 300 years. Tsunamis generated by such large quakes would be 15 to 25 feet high, or even higher. The rarity and magnitude of these quakes is thought to be caused by the locking of the fault zone, which allows stresses to build up so high that the eventual rupture is enormous. National Geographic, May 1998 v.193 n.5 p.6 (32).
Enrichment Topic 3. Mt. Ranier
The eruption and collapse of Mt. St. Helens in 1980 changes volcanologists’ understanding of volcanic processes. Investigation of prominent volcanoes, including Mt. Ranier, indicates that catastrophic gravitational collapses have occurred in the past, and are likely in the future.
Not only will the collapsing volcano affect the landscape immediately surrounding it, but rocky debris can be swept great distances from the source, creating tsunamis if it enters into the ocean. The study of Mt. St. Helens’ eruption in 1980 educated researchers that many volcanic deposits are the result of edifice failures and resulting volcanic avalanches. Researchers now acknowledge that of the 1500 volcanoes active during the Holocene, one-sixth of them have experienced edifice collapse. The US Geological Survey has made recent improvements to its educational programs as well as its methods for predicting collapses around Mt. Rainier. L. Siebert, “Blown Away,” Natural History, Oct. 2005, v.115 n.8 p. 50-55.
Enrichment Topic 3. Yellowstone
The Yellowstone Plateau is the product of three volcanic cycles, lasting about 2 million years. The first cycle, which produced the Huckleberry Ridge Tuff, about 2.1 million years ago, involved a cataclysmic eruption that spewed more than 2450 km3 of volcanic materials and created a 75 km long caldera (Island Park caldera). The second eruption, which produced the Mesa Falls Tuff, occurred 1.3 million years ago and formed the 16-km wide Henry Fork caldera. However, this was a smaller eruptive cycle—by Yellowstone standards. Volcanic activity then shifted to the Yellowstone Plateau. About 640,000 years ago, more than 1000 km3 of material was erupted to form the Lava Creek Tuff and the present caldera. Rhyolitic lava flows—from which Yellowstone gets its name—were erupted 150,000-70,000 years ago. A comparison diagram of the volumes produced by Yellowstone eruptions, compared to the catastrophic Krakatau in 1883 and the 1980 Mount St. Helens eruption, can be viewed at http://www.nps.gov/yell/naturescience/images/caldera_eruptions2_1.jpg . The United State Geological Survey also has additional information on Yellowstone at http://volcanoes.usgs.gov/yvo/about/index.php .
11. Crustal extension in the Basin and Range Province yielded north-south oriented, normal faults. Differential movement on these faults produced uplifted ranges separated by broad, sediment-filled basins.
Figure 16.15 The Basin and Range Province
12. The Colorado Plateau was deformed less than other areas in the Cordillera. Late Neogene uplift and erosion were responsible for the present topography of the region.
Figure 16.16 Rocks of the Colorado Plateau
13. The Rio Grande rift formed as north-south oriented rifting took place in an area extending from Colorado into Mexico. The basins within this rift filled with sediments and volcanic rocks.
Figure 16.17 The Rio Grande Rift
14. The westward drift of North America resulted in its collision with the Pacific-Farallon ridge. Subduction ceased, and the continental margin became bounded by major transform faults, except where the Juan de Fuca plate continues to collide with North America.
Figure 16.18 Origin
of the San Andreas and Queen Charlotte Faults
15. Sediments eroded from Laramide uplifts were deposited in intermontane basins, on
the Great Plains, and in a remnant of the Cretaceous epeiric seas in North Dakota.
Figure 16.19 Huge Amounts of Sediments Shed from the Laramide Highlands
Were Deposited on the Great Plains
Figure 16.20 Cenozoic Volcanism in the Great Plains
16. Cenozoic uplift and erosion were responsible for the present topography of the Appalachian Mountains. Much of the sediment eroded from the Appalachians was deposited on the Atlantic Coastal Plain.
Figure 16.21 Landsat Image of the Appalachian Mountains
Figure 16.22 Evolution of the Present Topography of the Appalachian
Mountains
17. Deposition on the Gulf Coastal Plain and Atlantic Coastal Plain took place throughout the Cenozoic, resulting in seaward-thickening wedges of rocks grading seaward from terrestrial facies to marine facies.
Figure 16.23 Cenozoic Deposition on the Gulf Coastal Plain
Figure 16.24 The
Continental Margin in Eastern North America
Figure
16.25 Sedimentary Rocks of the Atlantic
Coastal Plain
18. Paleogene and Neogene mineral resources include oil and natural gas, gold, and phosphorus-rich sedimentary rocks.
The Cenozoic Era
Types of Deformation
1. To demonstrate elastic deformation to a class, use a green twig or a large thick rubber band. For effect, continually deform it and allow it to rebound to the original shape while discussing the deformation with the class.
2. Plastic deformation is most easily demonstrated using Silly Putty® and pulling very slowly. Brittle deformation can be accomplished using either the twig or silly putty. Bend the twig until it snaps in a brittle fashion. Silly Putty® can be pulled very quickly or hit with a hammer in order to demonstrate brittle deformation.
3. Point out to the class the amount of time needed for these types of deformation to occur. Silly Putty® can be pulled slowly to demonstrate plastic deformation, while a sudden snap of the wrist will break the Silly Putty® and demonstrate brittle deformation.
Basin and Range
extension
Candy bars with a hard chocolate top and soft gooey caramel centers (such as Snickers®) make effective models for Basin and Range faulting. Stretch the candy bar so that the hard chocolate top breaks in a brittle fashion while the soft caramel center flows. The hard top represents the brittle part of the crust; the caramel represents the lower ductile crust.
1. How much extension has taken place in the Basin and Range? How much shortening and thickening took place during Sevier compressional tectonics? How would geologists calculate these figures?
2. If the Basin and Range Province is undergoing extension, is this area the beginning of a divergent plate boundary?
3. Consider movement along the San Andreas Fault. What will eventually happen to Southern California if the strike-slip movement continues?
4. What will happen to the North American continent if the Rio Grande Rift accelerates?
5. The Yellowstone hot spot and the Cascade volcanoes are geologically young and active. How does “human time” differ from “geologic time?” How can we reconcile the two time frames? Which time frame should we consider when planning for the safety of citizens living near a geologically active area?
|
Alpine-Himalayan orogenic belt |
Farallon plate |
|
Alpine orogeny |
Gulf Coastal Plain |
|
Atlantic Coastal Plain |
Laramide orogeny |
|
back-arc marginal basin |
North American Cordillera |
|
Basin and Range Province |
orogen |
|
Cascade Range |
Pacific-Farallon ridge |
|
circum-Pacific orogenic belt |
Rio Grande rift |
|
Colorado Plateau |
San Andreas transform fault |
|
continental interior |
Tejas epeiric sea Zuni epeiric sea |
1. In the Path of a Killer Volcano, PBS Home Video
2. Living Edens: Yellowstone, Sacred Wilderness, PBS Home Video
3. Supervolcano, The Discovery Channel
4. Exotic Terrane: Geological Discoveries in the Pacific Northwest, Bullfrog Films
5. Eruption of Mount St. Helens, IMAX
6. Fire Below Us: Remembering Mt. St. Helens, National Geographic
7. Ring of Fire, IMAX
8. Secret Yellowstone, National Geographic
9. Yellowstone: Imprints of Geologic Time, Terra
10. A Visit to St. Helens, Educational Images, Ltd.
1. Submarine Canyons and Deep Sea Fans, Educational Images, Ltd.
2. Satellite Imagery
– Earth from Space, slide set, Educational Images, Ltd.
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1. b |
5. c |
9. a |
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2. a |
6. d |
10. d |
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3. e |
7. a |
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4. c |
8. c |
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11. The Colorado Plateau is the vast, elevated region in Colorado, Utah, Arizona, and New Mexico. During the Paleogene, the Laramide deformation yielded broad anticlines and arches and basins, and a number of normal faults. However, deformation was far less intense than elsewhere in the Cordillera.
12. The Cascade Range begins in northern California, and continues through Oregon, Washington, and into British Columbia. Subduction of the Juan de Fuca Plate beneath the North American continent has resulted in the formation of a line of composite volcanoes.
13. The descending plate was subducted at a shallow angle beneath the continental lithosphere. Igneous activity shifted farther inland and finally ceased because the descending plate no longer penetrated to the mantle.
14. Both areas have horizontal or gently seaward-dipping strata deposited mostly by streams flowing across them. Seaward of the coastal plains are the continental shelf, slope, and rise. However, many of the sedimentary rocks in the Gulf Coastal Plain are either source rocks or reservoirs for hydrocarbons. The Gulf Coastal Plain was dominated by detrital deposition, but there was some carbonate deposition in the Florida section.
15. India broke away from Gondwana and began moving north in the Early Cretaceous. The subduction of oceanic lithosphere beneath Asia caused volcanism and plutonism in what is now Tibet. These volcanoes were destroyed as the Indian plate smashed into Asia, forming the Himalayan orogen. Since then India has been thrusting beneath Asia, causing crustal thickening and uplift.
16. The San Andreas Fault formed by migration of two triple junctions north and south, respectively, as the Pacific-Farallon Ridge subducted beneath the North American plate. The westward movement of the North American plate resulted in a collision with the Pacific-Farallon ridge. In southern California, two triple junctions formed, one at the intersection of the North American, Juan de Fuca, and Pacific plates, and the other at the intersection of the North American, Cocos, and Pacific plates. Continued westward movement of the North American plate over the Pacific plate cuased the triple junctions to migrate, one to the north and one to the south, giving rise to the San Andreas fault.
17. The Basin and Range Province is centered on
Nevada, but extends into the adjacent states and northern Mexico. Here, the
Earth’s crust has been stretched and thinned producing north-south oriented
mountain ranges with intervening basins.
Geologists have proposed several models to account for basin-and-range
structure, including back-arc spreading, spreading at the East Pacific Rise,
spreading above a mantle plume, and deformation related to movements along the
San Andreas fault.
18. Other than a brief period of marine
deposition early in the Cenozoic, sedimentation in the Great Plains took place
in terrestrial environments, especially fluvial systems. The only local
sediment source was the Black Hills in South Dakota.
19. A
back-arc marginal basin, such as that in the Sea of Japan, begins with
subduction at a convergent plate boundary. However, as the descending plate
reaches depth, partial melting will create magma, which will rise toward the
overriding plate. This rising magma may
initiate spreading within the overriding plate.
20. Africa
and Arabia moved north toward western Eurasia, pushing seafloor in front of
them, which was subducted under Eurasia. This zone is seismically active today.
In this region, collisional tectonics were complicated by the impact of several
terranes against southern Eurasia. Subduction in the eastern Mediterranean
resulted in a trench and active andesitic volcanism (Etna, Vesuvius).
Apply Your Knowledge
1. The
western coast of North America is an active continental margin, where
subduction is occurring as an oceanic plate is subducted beneath the North
American plate. Transform faults are also present. Therefore, because this region is along an
active boundary, it is associated with mountain building, volcanic activity,
and earthquakes. Glaciers form in higher
elevations, which are present in the young mountains. On the eastern coast of North America, a
passive continental margin exists. The eastern margin of North America lies
within a plate. Therefore, earthquakes,
volcanoes, and active mountain building are not found here. The situation was
reversed, in the Paleozoic Era. During the Paleozoic, the eastern coast of
North America was an active margin and the site of mountain building, while the
western margin was passive.
2. If the U.S. produces 8.45 billion barrels per day, and imports 12.36
million barrels of oil per day, then the total U.S. production/import is 20.81
million barrels per day (2.081 x 107 barrels per day). The Green River oil shales would contribute
80 billion barrels of oil, or 8.0 x 1010 barrels of oil. This would amount to 3844 days of US
production/import, or about 10.5 years of the current US production/import.
Problems with this projection include 1) the amount of petroleum use can
fluctuate, depending upon whether the US population conserves energy and/or
finds alternative energy sources; 2) the extraction of petroleum from oil
shales is not the same as extraction from sandstone reservoirs, and may present
technological problems, and/or greater expense in oil recovery.
3. (A metric ton is 1000 kg, although this information is not needed to calculate the answer.) If the US uses 1.0 billion tons annually, then the reserve of 250 billion metric tons should last
1 year / (1 x 109 metric tons) x (250 x 109 metric tons) = 250 years.
It is unlikely that the current rate of consumption will hold for 250 years. As the population increases, there are more demands on fuel reserves. Of course, we cannot predict whether more efficient methods of extracting energy from coal will exist in the future, or whether the rate of consumption will change as alternative energy sources are utilized. In addition, with current mining techniques, it is unlikely that the all of this reserve could be mined.
4. Student answers will vary greatly. For example, you could use large Earth slabs (plates), with one slab sliding beneath another. When the big piece of oceanic Earth (plate) moves far enough into the Earth, it begins to melt. The melted rock acts like the rising blobs in lava lamps, and comes toward the surface. This would produce volcanoes. However, if the angle of that descending slab of oceanic Earth does not go in steeply under the continent, it takes the slab of Earth (plate) a farther distance to get to the point where it is deep enough and hot enough to melt. So, the volcanoes would move farther in from the coast. Eventually, the slab of Earth (plate) does not go in steep enough to melt. So, although we may see deformation in the Rocky Mountains, volcanoes aren’t being produced.
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