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Historical Geology

 

CENOZOIC GEOLOGIC HISTORY:

THE PALEOGENE AND NEOGENE

 

OUTLINE

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

SUMMARY

 

 

CHAPTER OBJECTIVES

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.

 

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LEARNING OBJECTIVES

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

 

 

CHAPTER SUMMARY

   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

 

Enrichment Topic 2. The Dangers of the Pacific Northwest

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.

           

 

LECTURE SUGGESTIONS

 

The Cenozoic Era

 

  1. Although many major events have occurred in the Cenozoic Era, it might be a good idea to use a visual time line to remind students just how incredibly small the amount of time is contained in our modern era.  Only 1.4% of the Earth’s history is contained in the Cenozoic Era.

 

  1. After demonstrating the small amount of time contained in the Cenozoic Era, ask students to list ten important events in our human history, such as the founding of the United States of America and the building of the Great Pyramid. Place these historical items within the context of geological time. Although the Cenozoic Era represents on 1.4% of Earth’s history, recorded human history still constitutes only a minute part of 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.

 

CONSIDER THIS

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?

 


IMPORTANT TERMS

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

 

 

SUGGESTED MEDIA

Videos

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.

 

Slides and Demonstration Aids

   1.    Submarine Canyons and Deep Sea Fans, Educational Images, Ltd.

   2.    Satellite Imagery – Earth from Space, slide set, Educational Images, Ltd.

     

 

CHAPTER 16 - ANSWERS TO QUESTONS IN TEXT

Multiple Choice Review Questions

   1.    b

   5.    c

   9.    a

   2.    a

   6.    d

10.    d

   3.    e

   7.    a

 

   4.    c

   8.    c

 

 

 

 

Short Answer Essay Review Questions

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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