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Mesozoic Earth History


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Title: Mesozoic Earth History

Chapter 14
Mesozoic Earth History
Nevadan Orogeny and Gold
  • Approximately 150 to 210 million years after
  • the emplacement of massive plutons created the
    Sierra Nevada
  • Nevadan orogeny
  • gold was discovered at Sutter's Mill
  • on the South Fork of the American River at
    Coloma, California
  • On January 24, 1848, James Marshall,
  • a carpenter building a sawmill for John Sutter,
  • found bits of the glittering metal in the mill's

Gold Rush
  • Soon, settlements throughout the state
  • were completely abandoned as word
  • of the chance for instant riches
  • spread throughout California
  • Within a year after
  • the news of the gold discovery reached the East
  • the Sutter's Mill area was swarming with more
    than 80,000 prospectors,
  • all hoping to make their fortune

Gold Mining
  • By 1852,
  • mining operations were well underway
  • on the American River near Sacramento

Prospecting Was Very Hard Work
  • At least 250,000 gold seekers
  • prospected the Sutter's Mill area,
  • and although most were Americans,
  • they came from all over the world,
  • even as far away as China
  • Most of them thought
  • the gold was simply waiting to be taken,
  • and didn't realize that prospecting
  • was very hard work

Shopowners Made More Money
  • Of course, no one gave any thought
  • to the consequences of so many people converging
    on the Sutter's Mill area,
  • all intent on making easy money
  • In fact, life in the mining camps
  • was extremely hard and expensive
  • Frequently, the shop owners and traders
  • made more money than the prospectors

Abandoning Their Dream
  • In reality, only a small percentage of
  • ever hit it big
  • or were even moderately successful
  • The rest barely eked out a living
  • until they eventually abandoned their dream and
    went home

Placer Gold
  • The gold these prospectors sought was mostly in
    the form of placer deposits
  • Placer deposits form
  • when gold-bearing igneous rocks weather
  • and stream transport mechanically separates
  • by density
  • Although many prospectors searched for the mother
  • all of the gold recovered during the gold rush
    came from placers

Gold Panning
  • Panning is a common method of mining placer
  • In this method,
  • a shallow pan is dipped into a streambed,
  • the material is swirled around
  • and the lighter material is poured off
  • Gold, being about six times heavier
  • than most sand grains and rock chips,
  • concentrates on the bottom of the pan
  • and can then be picked out

200 million in gold
  • Although some prospectors
  • dug 30,000 worth of gold dust a week
  • out of a single claim
  • and some gold was found sitting on the surface
  • most of this easy gold was recovered
  • very early during the gold rush
  • Most prospectors made only a living wage working
    their claims
  • Nevertheless, during the five years
  • from 1848 to 1853
  • that constituted the gold rush proper,
  • miners extracted more than 200 million in gold

Mesozoic Era
  • The Mesozoic Era
  • 251 to 66 million years ago
  • was an important time in Earth history
  • The major geologic event
  • was the breakup of Pangaea,
  • which affected oceanic and climatic circulation
  • and influenced the evolution of the terrestrial
    and marine biotas

Other Mesozoic Events
  • Other important Mesozoic geologic events
  • resulting from plate movement
  • include
  • the origin of the Atlantic Ocean basin
  • and the Rocky Mountains
  • accumulation of vast salt deposits
  • that eventually formed salt domes
  • adjacent to which oil and natural gas were
  • and the emplacement of huge batholiths
  • accounting for the origin of various mineral

The Breakup of Pangaea
  • Just as the formation of Pangaea
  • influenced geologic and biologic events
  • during the Paleozoic,
  • the breakup of this supercontinent
  • profoundly affected geologic and biologic events
  • during the Mesozoic
  • The movement of continents
  • affected the global climatic and oceanic regimes
  • as well as the climates of the individual

Effect of the Breakup
  • Populations became isolated
  • or were brought into contact
  • with other populations,
  • leading to evolutionary changes in the biota
  • So great was the effect of this breakup
  • on the world,
  • that it forms the central theme of the Mesozoic

Progress of the Breakup
  • The breakup of Pangaea
  • began with rifting
  • between Laurasia and Gondwana during the Triassic
  • By the end of the Triassic,
  • the expanding Atlantic Ocean
  • separated North America from Africa
  • This change was followed
  • by the rifting of North America from South
  • sometime during the Late Triassic and Early

Paleogeography of the World
  • During the Triassic Period

Paleogeography of the World
  • During the Jurassic Period

Paleogeography of the World
  • During the Late Cretaceous Period

Oceans Responded to Continental Separation
  • Separation of the continents
  • allowed water from the Tethys Sea
  • to flow into the expanding central Atlantic
  • while Pacific Ocean waters
  • flowed into the newly formed Gulf of Mexico,
  • which at that time was little more than a
    restricted bay
  • Evaporites formed in these areas

Early Mesozoic Evaporites
  • Evaporites accumulated in shallow basins
  • as Pangaea broke apart during the Early Mesozoic
  • Water from the Tethys Sea flowed into the Central
    Atlantic Ocean

Early Mesozoic Evaporites
  • Water from the Pacific Ocean flowed into the the
    newly formed Gulf of Mexico
  • Marine water from the south flowed into the area
    that would eventually become the southern
    Atlantic Ocean

Evaporite Deposits
  • During that time, these areas were located
  • in the low tropical latitudes
  • where high temperatures
  • and high rates of evaporation
  • were ideal for the formation
  • of thick evaporite deposits

Further Breakup
  • During the Late Triassic and Jurassic periods,
  • Antarctica and Australia,
  • which remained sutured together,
  • began separating from South America and Africa
  • Also during this time,
  • India began rifting from the Gondwana continent
  • During the Jurassic,
  • South America and Africa began separating

Paleogeography of the World
  • During the Jurassic Period

Thick Evaporites from the Southern Ocean
  • The subsequent separation of South America and
  • formed a narrow basin
  • where thick evaporite deposits
  • accumulated from the evaporation
  • of southern ocean waters

Thick Southern Ocean Evaporites
  • Marine water flowed into the southern Atlantic
    Ocean from the south

Tethys Sea
  • During this time, the eastern end of the Tethys
  • began closing
  • as a result of the clockwise rotation
  • of Laurasia and the northward movement of Africa
  • This narrow Late Jurassic and Cretaceous seaway
  • between Africa and Europe
  • was the forerunner
  • of the present Mediterranean Sea

End of the Cretaceous
  • By the end of the Cretaceous,
  • Australia and Antarctica had separated,
  • India was nearly to the equator,
  • South America and Africa were widely separated,
  • and Greenland was essentially an independent

Paleogeography of the World
  • During the Late Cretaceous Period

Higher Heat Flow Caused Sea Level Rise
  • A global rise in sea level
  • during the Cretaceous
  • resulted in worldwide transgressions
  • onto the continents
  • These transgressions were caused
  • by higher heat flow along the oceanic ridges
  • caused by increased rifting
  • and the consequent expansion of oceanic crust

Middle Cretaceous Sea Level Was High
  • By the Middle Cretaceous,
  • sea level was probably as high
  • as at any time since the Ordovician,
  • and approximately one-third of the present land
  • was inundated by epeiric seas

Paleogeography of the World
  • During the Late Cretaceous Period

Final Stage in Pangaea's Breakup
  • The final stage in Pangaea's breakup
  • occurred during the Cenozoic
  • During this time,
  • Australia continued moving northward,
  • and Greenland completely separated
  • from Europe and North America
  • and formed a separate landmass

The Effects on Global Climates and Ocean
Circulation Patterns
  • By the end of the Permian Period,
  • Pangaea extended from pole to pole,
  • covered about one-fourth of Earth's surface,
  • and was surrounded by Panthalassa,
  • a global ocean that encompassed about 300 degrees
    of longitude
  • Such a configuration exerted tremendous influence
  • on the world's climate
  • and resulted in generally arid conditions
  • over large parts of Pangaea's interior

Paleogeography of the World
  • For the Late Permian Period

Ocean Currents and Continents
  • The world's climates result from the complex
    interaction between
  • wind and ocean currents
  • and the location and topography of the continents
  • In general, dry climates occur
  • on large landmasses
  • in areas remote from sources of moisture
  • and where barriers to moist air exist,
  • such as mountain ranges
  • Wet climates occur
  • near large bodies of water
  • or where winds can carry moist air over land

Climate-Sensitive Deposits
  • Past climatic conditions can be inferred from
  • the distribution of climate-sensitive deposits
  • Evaporites are deposited
  • where evaporation exceeds precipitation
  • While dunes and red beds
  • may form locally in humid regions,
  • they are characteristic of arid regions
  • Coal forms in both warm and cool humid climates
  • Vegetation that is eventually converted into coal
  • requires at least a good seasonal water supply
  • Thus, coal deposits are indicative of humid

Evaporites, Red Beds, Dunes, Coal
  • Widespread Triassic evaporites, red beds, and
    desert dunes
  • in the low and middle latitudes
  • of North and South America, Europe, and Africa
  • indicate dry climates in those regions,
  • while coal deposits
  • are found mainly in the high latitudes,
  • indicating humid conditions
  • These high-latitude coals are analogous to
  • today's Scottish peat bog
  • or Canadian muskeg

Bordering the Tethys Sea
  • The lands bordering the Tethys Sea
  • were probably dominated by seasonal monsoon rains
  • resulting from the warm, moist winds
  • and warm oceanic currents
  • impinging against the east-facing coast of

Faster Circulation
  • The temperature gradient
  • between the tropics and the poles
  • also affects oceanic and atmospheric circulation
  • The greater the temperature difference
  • between the tropics and the poles,
  • the steeper the temperature gradient
  • and the faster the circulation of the oceans and

Global Temperature Gradient
  • The breakup of Pangaea
  • during the Late Triassic
  • caused the global temperature gradient to
  • because the Northern Hemisphere continents
  • moved farther northward,
  • displacing higher-latitude ocean waters
  • Decrease in temperature in the high latitudes
  • and the changing positions of the continents,
  • caused the steeper global temperature gradient
  • Thus, oceanic and atmospheric circulation
  • greatly accelerated during the Mesozoic

Oceanic Circulation Evolved
  • From a simple pattern in a single ocean
    (Panthalassa) with a single continent (Pangaea)

Oceanic Circulation Evolved
  • to a more complex pattern in the newly formed
    oceans of the Cretaceous Period

Areas Dominated by Seas are Warmer
  • Oceans absorb about 90 of the solar radiation
    they receive,
  • while continents absorb only about 50,
  • even less if they are snow covered
  • The rest of the solar radiation is reflected back
    into space
  • Therefore, areas dominated by seas are warmer
  • than those dominated by continents

Oceans Still Quite Warm
  • By knowing the distribution of continents and
    ocean basins,
  • geologists can generally estimate
  • the average annual temperature
  • for any region on Earth,
  • as well as determining a temperature gradient
  • Though the temperature gradient and seasonality
    on land
  • were increasing during the Jurassic and
  • the middle- and higher-latitude oceans
  • were still quite warm

Equable Worldwide Climate
  • Higher-latitude oceans remained warm
  • because warm waters from the Tethys Sea
  • were circulating to the higher latitudes
  • The result was a relatively equable worldwide
  • through the end of the Cretaceous

The Mesozoic History of North America
  • In North America, the beginning of the Mesozoic
  • was essentially the same in terms of tectonism
    and sedimentation
  • as the preceding Permian Period
  • Terrestrial sedimentation continued over much of
    the craton,
  • while block faulting and igneous activity
  • began in the Appalachian region
  • as North America and Africa began separating

Permian Period
  • Paleogeography of North America during the
    Permian Period

Triassic Period
  • Paleogeography of North America during the
    Triassic Period

Gulf of Mexico
  • The newly forming Gulf of Mexico
  • experienced extensive evaporite deposition
  • during the Late Triassic and Jurassic
  • as North America separated from South America

Jurassic Period
  • Paleogeography of North America during the
    Jurassic Period

Global Sea-Level Rise
  • A global rise in sea level
  • during the Cretaceous
  • resulted in worldwide transgressions
  • onto the continents such that marine deposition
  • was continuous over much of the North American

Volcanic Island Arc at the Western Edge of the
  • A volcanic island arc system
  • that formed off the western edge of the craton
  • during the Permian
  • was sutured to North America
  • sometime later during the Permian or Triassic
  • This event is referred to as the Sonoma orogeny

Cordilleran Area
  • During the Jurassic,
  • the entire Cordilleran area
  • was involved in a series
  • of major mountain-building episodes
  • that result in the formation of the Sierra
  • the Rocky Mountains,
  • and other lesser mountain ranges
  • Although each orogenic episode
  • has its own name,
  • the entire mountain-building event
  • is simply called the Cordilleran orogeny

Next, Specific Regions
  • Keeping in mind this simplified overview
  • of the Mesozoic history of North America,
  • we will now examine the specific regions of the

Continental Interior
  • Recall that the history of the North American
  • can be divided into unconformity-bound sequences
  • reflecting advances and retreats of epeiric seas
  • over the craton
  • While these transgressions and regressions
  • played a major role in the Paleozoic geologic
    history of the continent,
  • they were not as important during the Mesozoic

Cratonic Sequences of North America
  • White areas represent sequences of rocks
  • that are separated by large-scale uncon-formities
  • shown in brown

Continental Interior With Inundation
  • Cratonic sequences are less important because
  • most of the continental interior
  • during the Mesozoic
  • was well above sea level
  • and did not experience epeiric sea inundation
  • As we examine the Mesozoic history
  • of the continental margin regions of North
  • we will combine the two cratonic sequences,
  • the Absaroka Sequence
  • Late Mississippian to Early Jurassic
  • and Zuni Sequence
  • Early Jurassic to Early Paleocene

Cratonic Sequences of North America
  • Absaroka sequence
  • Zuni sequence

Eastern Coastal Region
  • During the Early and Middle Triassic,
  • coarse detrital sediments derived from the
    erosion of the recently uplifted Appalachians
  • Alleghenian Orogeny
  • filled the various intermontane basins
  • and spread over the surrounding areas
  • As erosion continued during the Mesozoic,
  • this once lofty mountain system was reduced to a
    low-lying plain

Fault-block Basins
  • During the Late Triassic,
  • the first stage in the breakup of Pangaea began
  • with North America separating from Africa
  • Fault-block basins developed
  • in response to upwelling magma
  • beneath Pangaea
  • in a zone stretching
  • from present-day Nova Scotia to North Carolina

Triassic Fault Basins
  • Areas where Triassic fault-block basin deposits
  • crop out in eastern North America

Fault-Block Basins
  • After the Appalachians were eroded to a low-lying
  • by the Middle Triassic,
  • fault-block basins formed
  • as a result of Late Triassic rifting
  • between North America and Africa

Newark Group
  • Erosion of the adjacent fault-block mountains
  • filled these basins with great quantities
  • up to 6000 m
  • of poorly sorted red nonmarine detrital sediments
  • known as the Newark Group

Down-dropped valleys accumulated sediments
  • Down-dropped valleys accumulated tremendous
    thickness of sediments
  • and were themselves broken
  • by a complex of normal faults during rifting

Reptile Footprints
  • Reptiles roamed along the margins
  • of the various lakes and streams
  • that formed in these basins,
  • leaving their footprints and trackways
  • in the soft sediments
  • Although the Newark Group rocks contain numerous
    dinosaur footprints,
  • they are almost completely devoid of dinosaur
  • The Newark Group is mostly Late Triassic,
  • but in some areas deposition began in the Early

Reptile Tracks
  • Reptile tracks in the Triassic Newark Group
  • were uncovered during the excavation
  • for a new state building in Hartford, Connecticut
  • Because the tracks were so spectacular,
  • the building side was moved
  • and the excavation was designated as a state park

Reptile Tracks
Igneous Activity
  • Concurrent with sedimentation
  • in the fault-block basins
  • were extensive lava flows
  • that blanketed the basin floors
  • as well as intrusions of numerous dikes and sills
  • The most famous intrusion
  • is the prominent Palisades sill
  • along the Hudson River
  • in the New York-New Jersey area

Palisades Sill of the Hudson River
  • This sill was one of many that were intruded into
    the Newark sediments
  • during the Late Triassic rifting
  • that marked the separation
  • of North America from Africa

Passive Continental Margin
  • As the Atlantic Ocean grew,
  • rifting ceased along the eastern margin
  • of North America,
  • and this once active plate margin
  • became a passive, trailing continental margin
  • The fault-block mountains
  • that were produced by this rifting
  • continued eroding
  • during the Jurassic and Early Cretaceous
  • until all that was left was a large low-relief

Eastern Continental Shelf
  • The sediments produced
  • by this erosion
  • contributed to the growing eastern continental
  • During the Cretaceous Period,
  • the Appalachian region was re-elevated
  • and once again shed sediments
  • onto the continental shelf,
  • forming a gently dipping,
  • seaward-thickening wedge of rocks
  • up to 3000 m thick

Seaward-Thickening Wedge
  • The seaward-thickening wedge of rocks
  • is currently exposed
  • in a belt extending from
  • Long Island, New York,
  • to Georgia

Gulf Coastal Region
  • Paleogeographic Map of North America during the
    Triassic Period
  • The Gulf Coastal region was above sea level until
    the Late Triassic
  • -

Evaporites in Gulf of Mexico
  • As North America separated from South America
  • during the Late Triassic and Early Jurassic,
  • the Gulf of Mexico began to form
  • With oceanic waters flowing into
  • this newly formed, shallow, restricted basin,
  • conditions were ideal for evaporite formation
  • These Jurassic evaporites
  • are thought to be the source
  • for the Paleogene salt domes
  • found today in the Gulf of Mexico and southern

Jurassic Period
  • Paleogeographic reconstruction for the Jurassic
  • The Gulf of Mexico began to form
  • with the precipitation of evaporites

Paleogene Salt Domes
Evaporite Deposition Ended
  • The history of the Paleogene salt domes
  • and their associated petroleum accumulations
  • will be discussed with the Cenozoic
  • By the Late Jurassic,
  • circulation in the Gulf of Mexico
  • was less restricted,
  • and evaporite deposition ended

Normal Marine Conditions
  • Normal marine conditions
  • returned to the area
  • with alternating transgressing and regressing
  • The resulting sediments were
  • covered and buried by thousands of meters
  • of Cretaceous and Cenozoic sediments
  • During the Cretaceous,
  • the Gulf Coastal region,
  • like the rest of the continental margin,
  • was flooded by northward-transgressing seas

Cretaceous Period
  • Paleogeography of North America during the
    Cretaceous Period
  • with its northward-transgressing seas

Transgressions and Regression
  • As a result of the transgression,
  • nearshore sandstones
  • are overlain by finer sediments
  • characteristic of deeper waters
  • Following an extensive regression
  • at the end of the Early Cretaceous,
  • a major transgression began
  • during which a wide seaway extended
  • from the Arctic Ocean to the Gulf of Mexico
  • Sediments that were deposited in the Gulf Coastal
  • formed a seaward-thickening wedge

Cretaceous Period
  • Paleogeography of North America during the
    Cretaceous Period
  • Cretaceous Interior Seaway

Cretaceous Bivalve Reefs
  • Reefs were also widespread
  • in the Gulf Coastal region during the Cretaceous
  • Bivalves called rudists
  • were the main constituent
  • of many of these reefs
  • Because of their high porosity and permeability,
  • rudistoid reefs make excellent petroleum
  • A good example of a Cretaceous reef complex
    occurs in Texas

Reef-Building Bivalves
  • Two genera of Cretaceous bivalves known as
    rudists replaced corals as the main reef-building
    animals of the Mesozoic

Gulf Shelf-Margin Facies
  • Early Cretaceous shelf-margin facies around the
    Gulf of Mexico Basin
  • The reef trend shows as a black line

Reef Environments
  • Depositional environment and facies changes
    across the Stuart City reef trend, South Texas

Rudist Reef Facies Patterns
  • Here the reef trend
  • had a strong influence
  • on the carbonate platform deposition of the
  • The facies patterns of these carbonate rocks
  • are as complex as those found
  • in the major barrier-reef systems
  • of the Paleozoic Era

Western RegionMesozoic Tectonics
  • The Mesozoic geologic history
  • of the North American Cordilleran mobile belt
  • is very complex,
  • involving the eastward subduction
  • of the oceanic Farallon plate
  • under the continental North American plate
  • Activity along this oceanic-continental
    convergent plate boundary,
  • resulted in an eastward movement of deformation

Cordilleran Orogenic Activity
  • This orogenic activity
  • progressively affected
  • the trench and continental slope, the continental
    shelf, and the cratonic margin,
  • causing a thickening of the continental crust
  • The accretion of terranes and microplates
  • played a significant role in this area

Sonoma Orogeny
  • Except for the Late Devonian-Early Mississippian
    Antler orogeny,
  • the Cordilleran region of North America
    experienced little tectonism during the Paleozoic
  • During the Permian, however, an island arc and
    ocean basin formed
  • off the western North American craton
  • followed by subduction of an oceanic plate
  • beneath the island arc
  • and the thrusting of oceanic and island arc rocks
  • eastward against the craton margin

Sonoma Orogeny
  • This event, known as the Sonoma orogeny,
  • occurred at or near the Permian-Triassic boundary
  • and resulted in the suturing of island-arc
  • along the western edge of North America.

Triassic Period
  • Paleogeography of North America during the
    Triassic Period
  • with a volcanic island arc in the west

Sonoma Orogeny
  • Tectonic activity that culminated
  • in the Permian-Triassic Sonoma orogeny
  • in western North America
  • was the result of a collision
  • between the southwestern margin of North America
  • and an island arc system

Oceanic-Continental Convergent Plate Boundary
  • Following the Late Paleozoic-Early Mesozoic
  • destruction of the volcanic island arc
  • during the Sonoma orogeny,
  • the western margin of North America
  • became an oceanic-continental convergent plate

Steeply Dipping Subduction Zone
  • During the Late Triassic,
  • a steeply dipping subduction zone developed
  • along the western margin of North America
  • in response to the westward movement
  • of North America over the Farallon plate
  • This newly created oceanic-continental plate
  • controlled Cordilleran tectonics
  • for the rest of the Mesozoic Era
  • and for most of the Cenozoic Era
  • This subduction zone marks the beginning
  • of the modern circum-Pacific orogenic system

Steeply Dipping Subduction Zone
  • Interpretation of the tectonic setting
  • of western North America
  • during the Late Triassic to Early Jurassic
  • Plutons of the Sierra Nevada began forming

Two Subduction Zones
  • Two subduction zones,
  • dipping in opposite directions from each other,
  • formed off the west coast of North America
  • during the Middle and early Late Jurassic

The North American Overrode the Farallon Plate
  • The more westerly subduction zone
  • was eliminated
  • by the westward-moving North American plate,
  • which overrode the oceanic Farallon plate

Continued Tectonic Evolution
Franciscan Complex
  • The Franciscan Complex, California,
  • which is up to 7000 m thick,
  • is an unusual rock unit
  • consisting of a chaotic mixture of rocks
  • that accumulated during the Late Jurassic and
  • The various rock types include
  • graywacke, volcanic breccia, siltstone, black
  • chert, pillow basalt, and blueschist metamorphic
  • a low temperature, high pressure metamorphic rock

Franciscan Complex
  • The rock types suggest
  • that continental shelf, slope, and deep-sea
  • were brought together
  • in a submarine trench
  • when North America overrode the subducting
    Farallon plate

Franciscan Complex
  • Map showing the location of the Franciscan Complex

Depositional Environment
  • Reconstruction of the depositional environment
  • of the Franciscan Complex
  • during the Late Jurassic and Cretaceous periods

Franciscan Complex
  • Exposures of the Franciscan Complex along the
    central California coast

Great Valley Group
  • East of the Franciscan Complex
  • and currently separated from it
  • by a major thrust fault
  • is the Great Valley Group
  • It consists of more than 16,000 m
  • of conglomerates, sandstones, siltstones, and
  • These sediments were deposited
  • on the continental shelf and slope
  • at the same time the Franciscan deposits
  • were accumulating in the submarine trench

Great Valley Group Environment
  • Environments of the Great Valley Group
  • in relation to the Franciscan Complex

Cordilleran Orogeny
  • The general term Cordilleran orogeny
  • is applied to the mountain-building activity
  • that began during the Jurassic
  • and continued into the Cenozoic
  • The Cordilleran orogeny
  • consisted of a series
  • of individual mountain-building events
  • that occurred in different regions at different
  • Most of this Cordilleran orogenic activity
  • is related to the continued westward movement of
    the North American plate

Cordilleran Mobile Belt
  • Mesozoic orogenies
  • occurring in the Cordilleran mobile belt

Nevadan Orogeny
  • The first phase of the Cordilleran orogeny,
  • the Nevadan orogeny,
  • began during the Late Jurassic
  • and continued into the Cretaceous
  • as large volumes of granitic magma
  • were generated at depth
  • beneath the western edge of North America
  • These granitic masses
  • ascended as huge batholiths
  • that are now recognized as
  • the Sierra Nevada, Southern California, Idaho,
    and Coast Range batholiths

Cordilleran Mobile Belt
  • Mesozoic orogenies
  • occurring in the Cordilleran mobile belt

  • Location of Jurassic and Cretaceous batholiths
  • in western North America

Plutonic Activity Migrated Eastward
  • By the Late Cretaceous,
  • most of the volcanic and plutonic activity
  • had migrated eastward into Nevada and Idaho
  • This migration was probably caused
  • by a change from high-angle to low-angle
  • resulting in the subducting oceanic plate
  • reaching its melting depth farther east

Eastward Migrating
  • A possible cause
  • for the eastward migration
  • of Cordilleran igneous activity
  • during the Cretaceous
  • was a change from high angle subduction to

Lower-Angle Subduction
  • to low-angle subduction
  • As the subducting plate
  • moved downward
  • at a lower angle,
  • its melting depth
  • moved farther to the east

Sevier Orogeny
  • Thrusting occurred progressively farther east
  • so that by the Late Cretaceous,
  • it extended all the way
  • to the Idaho-Washington border
  • The second phase of the Cordilleran orogeny,
  • the Sevier orogeny,
  • was mostly a Cretaceous event

Cordilleran Mobile Belt
  • Mesozoic orogenies
  • occurring in the Cordilleran mobile belt

Thrust Faults
  • Subduction of the Farallon plate
  • beneath the North American plate continued during
    this time,
  • resulting in numerous overlapping,
  • low-angle thrust faults
  • in which blocks of older strata
  • were thrust eastward
  • on top of younger strata
  • This deformation produced
  • generally north-south-trending mountain ranges
  • that stretch from Montana to western Canada

Sevier Orogeny
  • Associated tectonic features
  • of the Late Cretaceous Sevier orogeny
  • caused by subduction of the Farallon plate
  • under the North American plate

Keystone Thrust Fault
Keystone Thrust Fault
  • The Keystone thrust fault is a major fault in the
    Sevier overthrust belt
  • It is exposed west of Las Vagas, Nevada
  • The sharp boundary
  • between the light-colored Mesozoic rocks
  • and the overlying dark-colored Paleozoic rocks
  • marks the trace of the Keystone thrust fault

Keystone Thrust Fault
Laramide orogeny
  • During the Late Cretaceous to Early Cenozoic,
  • the final pulse of the Cordilleran orogeny
  • The Laramide orogeny
  • developed east of the Sevier orogenic belt
  • in the present-day Rocky Mountain areas
  • of New Mexico, Colorado, and Wyoming

Cordilleran Mobile Belt
  • Mesozoic orogenies
  • occurring in the Cordilleran mobile belt

Present-Day Rocky Mountains
  • Most of the features
  • of the present-day Rocky Mountains
  • resulted from the Cenozoic phase
  • of the Laramide orogeny

Mesozoic Sedimentation
  • Concurrent with the tectonism
  • in the Cordilleran mobile belt,
  • Early Triassic sedimentation
  • on the western continental shelf
  • consisted of shallow-water marine
  • sandstones, shales, and limestones
  • During the Middle and Late Triassic,
  • the western shallow seas
  • regressed farther west,
  • exposing large areas of former seafloor to erosion

Marine and Nonmarine Triassic Rocks
  • Marginal marine and nonmarine Triassic rocks,
  • particularly red beds,
  • contribute to the spectacular
  • and colorful scenery of the region
  • The Lower Triassic Moenkopi Formation
  • of the southwestern United States
  • consists of a succession of brick-red
  • and chocolate-colored mudstones

Triassic and Jurassic Formations
  • Triassic and Jurassic formations in the western
    United States

Sedimentary Structures
  • Such sedimentary structures
  • as desiccation cracks and ripple marks,
  • as well as fossil amphibians and reptiles and
    their tracks,
  • indicate deposition in a variety of continental
  • including stream channels, floodplains, and fresh
    and brackish water ponds
  • Thin tongues of marine limestones
  • indicate brief incursions of the sea,
  • while local beds with gypsum and halite crystal
  • attest to a rather arid climate

Shinarump and Chinle
  • Unconformably overlying the Moenkopi
  • is the Upper Triassic Shinarump Conglomerate,
  • a widespread unit generally less than 50 m thick
  • Above the Shinarump
  • are the multicolored shales, siltstones, and
  • of the Upper Triassic Chinle Formation
  • This formation is widely exposed
  • throughout the Colorado Plateau
  • and is probably most famous for its petrified
  • spectacularly exposed in Petrified Forest
    National Park, Arizona

Triassic and Jurassic Formations
  • Triassic and Jurassic formations in the western
    United States

Petrified Wood and Plants Fossils
  • Whereas fossil ferns are found here,
  • the park is best known for
  • its abundant and beautifully preserved logs
  • of gymnosperms especially conifers
  • and plants called cycads
  • Fossilization resulted from the silicification of
    the plant tissues
  • Weathering of volcanic ash beds
  • interbedded with fluvial and deltaic Chinle
  • provided most of the silica for silicification

  • Some trees were preserved in place,
  • but most were transported during floods
  • and deposited on sandbars
  • and on floodplains,
  • where fossilization took place
  • After burial, silica-rich groundwater
  • percolated through the sediments
  • and silicified the wood

Other Fossils
  • Though best known for its petrified wood, the
    Chinle Formation has also yielded fossils of
  • labyrinthodont amphibians,
  • phytosaurs,
  • and small dinosaurs

Upward in the Stratigraphy
  • The Wingate Sandstone,
  • a desert dune deposit,
  • and the Kayenta Formation,
  • a stream and lake deposit,
  • overlie the Chinle Formation
  • These two formations are well exposed
  • in southwestern Utah

Triassic and Jurassic Formations
  • Triassic and Jurassic formations in the western
    United States

Early Jurassic Sandstones
  • The thickest and most prominent of the Jurassic
    cross-bedded sandstones
  • is the Navajo Sandstone,
  • a widespread formation
  • that accumulated in a coastal dune environment
  • along the southwestern margin of the craton

Navajo Sandstone, Zion Canyon
Navajo Sandstone, Zion Canyon
  • View of East Entrance of Zion Canyon, Zion
    National Park, Utah
  • The light-colored massive rocks
  • are the Jurassic Navajo Sandstone
  • while the slope-forming rocks below the Navajo
  • are the Upper Triassic Kayenta Formation

Navajo Sandstone, Zion Canyon
Navajo Sandstone's Large-Scale Cross-Beds
  • The Navajo Sandstone's most distinguishing
  • is its large-scale cross-beds,
  • some of which are more than 25 m high

Navajo Sandstone
  • Large cross-beds of the Jurassic Navajo Sandstone
    in Zion National Park, Utah

Sundance Sea
  • The upper part of the Navajo
  • contains smaller cross-beds
  • as well as dinosaur and crocodilian fossils
  • Marine conditions returned to the region
  • during the Middle Jurassic
  • when a seaway called the Sundance Sea
  • twice flooded the interior of western North

Sundance Sea
  • The resulting deposits,
  • the Sundance Formation,
  • were produced from erosion
  • of tectonic highlands to the west
  • that paralleled the shoreline

Sundance Sea Retreated Northward
  • These highlands
  • resulted from intrusive igneous activity
  • and associated volcanism
  • that began during the Triassic
  • During the Late Jurassic,
  • a mountain chain formed
  • in Nevada, Utah, and Idaho
  • as a result of the deformation
  • produced by the Nevadan orogeny
  • As the mountain chain grew
  • and shed sediments eastward,
  • the Sundance Sea began retreating northward

Morrison Formation
  • A large part of the area
  • formerly occupied by the Sundance Sea
  • was then covered
  • by multicolored sandstones, mudstones, shales,
    and occasional lenses of conglomerates
  • that comprise the world-famous Morrison Formation
  • The Morrison Formation
  • contains the world's richest assemblage
  • of Jurassic dinosaur remains

Morrison Formation
  • View of the Jurassic Morrison Formation
  • from the Visitors center
  • at Dinosaur National Monument, Utah

Skeletons Deposited on Sandbars
  • Although most of the dinosaur skeletons
  • are broken up,
  • as many as 50 individuals
  • have been found together in a small area
  • Such a concentration indicates
  • that the skeletons were brought together
  • during times of flooding and deposited on
  • in stream channels
  • Soils in the Morrison indicate
  • that the climate was seasonably dry

Dinosaur National Monument
  • Although most major museums have either
  • complete dinosaur skeletons
  • or at least bones from the Morrison Formation,
  • the best place to see the bones still embedded in
    the rocks
  • is the visitors' center at Dinosaur National
    Monument near Vernal, Utah
  • The north wall of the visitors center
  • shows dinosaur bones in bas relief
  • just as they were deposited 140 million years ago

North Wall
Mid-Cretaceous Transgressions
  • Shortly before the end of the Early Cretaceous,
  • Arctic waters spread southward
  • over the craton, forming a large inland sea
  • in the Cordilleran foreland basin area
  • Mid-Cretaceous transgressions
  • also occurred on other continents,
  • and all were part of the global mid-Cretaceous
  • rise in sea level
  • that resulted from accelerated seafloor spreading
  • as Pangaea continued to fragment

Cretaceous Interior Seaway
  • By the beginning of the Late Cretaceous,
  • this incursion
  • joined the northward-transgressing waters from
    the Gulf area
  • to create an enormous Cretaceous Interior Seaway
  • that occupied the area east of the Sevier
    orogenic belt

Cretaceous Interior Seaway
  • Extending from the Gulf of Mexico
  • to the Arctic Ocean
  • and more than 1500 km wide at its maximum extent,
  • this seaway
  • effectively divided North America
  • into two large landmasses
  • until just before the end of the Late Cretaceous

Cretaceous Interior Seaway
  • Paleogeography of North America during the
    Cretaceous Period
  • Cretaceous Interior Seaway

Cretaceous deposits
  • Cretaceous deposits
  • less than 100 m thick indicate
  • that the eastern margin of the Cretaceous
    Interior Seaway
  • subsided slowly
  • and received little sediment
  • from the emergent, low-relief craton to the east
  • The western shoreline, however,
  • shifted back and forth,
  • primarily in response to fluctuations
  • in the supply of sediment
  • from the Cordilleran Sevier orogenic belt to the

Facies Relationships
  • The facies relationships
  • show lateral changes
  • from conglomerate and coarse sandstone adjacent
    to the mountain belt
  • through finer sandstones, siltstones, shales,
  • and even limestones and chalks in the east
  • During times of particularly active mountain
  • these coarse clastic wedges of gravel and sand
  • prograded even further east

Cretaceous Facies Related to Sevier
  • This restored west-east cross section
  • of Cretaceous facies of the western Cretaceous
    Interior Seaway
  • shows the facies relationship to the Sevier
    orogenic belt

Cretaceous Interior Seaway
  • As the Mesozoic Era ended,
  • the Cretaceous Interior Seaway
  • withdrew from the craton.
  • During the regression,
  • marine waters retreated to the north and south,
  • and marginal marine and continental deposition
  • formed widespread coal-bearing deposits
  • on the coastal plain.

Accretion of Terranes
  • Orogenies along convergent plate boundaries
  • resulted in continental accretion
  • Much of the material accreted to continents
  • during such events is simply eroded older
    continental crust,
  • but a significant amount of new material
  • is added to continents
  • such as igneous rocks that formed as a
  • of subduction and partial melting

Accretion of Terranes
  • Although subduction
  • is the predominant influence
  • on the tectonic history
  • in many regions of orogenesis,
  • other processes are also involved
  • in mountain building
  • and continental accretion,
  • especially the accretion of terranes

  • Geologists now know that portions of many
    mountain systems
  • are composed of small accreted lithospheric
  • that are clearly of foreign origin
  • These terranes
  • differ completely in their fossil content,
  • stratigraphy, structural trends,
  • and paleomagnetic properties
  • from the rocks
  • of the surrounding mountain system
  • and adjacent craton

Accretion of Terranes
  • In fact, terranes are so different from adjacent
  • that most geologists think they formed elsewhere
  • and were carried great distances
  • as parts of other plates
  • until they collided
  • with other terranes or continents
  • Geologic evidence indicates
  • that more than 25
  • of the entire Pacific Coast
  • from Alaska to Baja California
  • consists of accreted terranes

Accretion of Terranes
  • The accreting terranes
  • are composed of volcanic island arcs,
  • oceanic ridges,
  • seamounts,
  • volcanic plateaus,
  • hot spot tracks,
  • and small fragments of continents
  • that were scraped off and accreted
  • to the continent's margin
  • as the oceanic plate with which they were carried
  • was subducted under the continent

More Than 100 Terranes
  • It is estimated that more than 100
    different-sized terranes
  • have been added to the western margin
  • of North America
  • during the last 200 million years
  • Good examples of this
  • are the Wrangellian terranes
  • which have been accreted
  • to North America's western margin

Terranes of Western North America
  • Some of the accreted lithospheric blocks
  • called terranes
  • that form the western margin
  • of the North American Craton
  • The dark brown blocks
  • probably originated as terranes
  • and were accreted to North America

Terranes of Western North America
  • The light green blocks
  • are possibly displaced parts of North America
  • Dark green
  • represents the North American craton

Growth along Active Margins
  • The basic plate tectonic reconstruction
  • of orogenies and continental accretion
  • remains unchanged,
  • but the details of such reconstructions
  • are decidedly different
  • in view of terrane tectonics
  • For example, growth along active continental
  • is faster than along passive continental margins
  • because of the accretion of terranes

New Additions
  • Furthermore, these accreted microplates
  • are often new additions to a continent,
  • rather than reworked older continental material
  • So far, most terranes
  • have been identified in mountains
  • of the North American Pacific Coast region,
  • but a number of such plates are suspected
  • to be present in other mountain systems as well
  • They are more difficult to recognize in older
    mountain systems,
  • such as the Appalachians, however,
  • because of greater deformation and erosion

  • Thus, terranes
  • provide another way
  • of viewing Earth
  • and gaining a better understanding
  • of the geologic history of the continents

Mesozoic Mineral Resources
  • Although much of the coal in North America
  • is Pennsylvanian or Tertiary in age,
  • important Mesozoic coals
  • occur in the Rocky Mountains states
  • These are mostly lignite and bituminous coals,
  • but some local anthracites are present as well
  • Particularly widespread in western North American
  • are coals of Cretaceous age
  • Mesozoic coals are also known
  • from Alberta and British Columbia, Canada,
  • as well as from Australia, Russia, and China

Petroleum in Gulfs
  • Large concentrations of petroleum
  • occur in many areas of the world,
  • but more than 50 of all proven reserves
  • are in the Persian Gulf region
  • During the Mesozoic Era,
  • what is now the Gulf region
  • was a broad passive continental margin
  • conducive for the formation of petroleum
  • Similar conditions existed in what is now the
    Gulf Coast region
  • of the United States and Central America

Gulf Coast Region
  • Here, petroleum and natural gas
  • also formed on a broad shelf
  • over which transgressions and regressions
  • In this region, the hydrocarbons
  • are largely in reservoir rocks
  • that were deposited
  • as distributary channels on deltas
  • and as barrier-island and beach sands
  • Some of these hydrocarbons are associated
  • with structures formed adjacent to rising salt

Louann Salt
  • The salt, called the Louann Salt,
  • initially formed in a long, narrow sea
  • when North America separated from Europe and
    North Africa
  • during the fragmentation of Pangaea

  • Salt deposits in the Gulf of Mexico
  • formed during the initial opening of the Atlantic

Uranium Ores
  • The richest uranium ores in the United States
  • are widespread in Mesozoic rocks
  • of the Colorado Plateau area of Colorado
  • and adjoining parts of Wyoming, Utah, Arizona,
    and New Mexico
  • These ores, consisting of fairly pure masses
  • of a complex potassium-, uranium-,
    vanadium-bearing mineral
  • called carnotite,
  • are associated with plant remains in sandstones
  • that were deposited in ancient stream channels

Mesozoic Iron Ores
  • Proterozoic banded iron formations
  • are the main sources of iron ores
  • Exceptions exist such as
  • the Jurassic-age "Minette" iron ores of Western
  • which are composed of oolitic limonite and
  • and are important ores in France, Germany,
    Belgium, and Luxembourg
  • In Great Britain, low-grade Jurassic iron ores
  • consist of oolitic siderite, wh
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