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					    Chapter 14


Mesozoic Earth History
      Mesozoic Era 251-66 MYA

• The major geologic event
  – was the breakup of Pangaea,
  – affected oceanic and climatic circulation patterns
  – 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 trapped
  – and the emplacement of huge batholiths
     • accounting for the origin of various mineral resources
          Effect of the Breakup

• Populations became isolated
  – or were brought into contact with other
    populations, leading to evolutionary changes in
    the biota
        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
    America
     • sometime during the Late Triassic and Early Jurassic
    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
          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
    Paleogeography of the World
• During the Jurassic Period
                  Tethys Sea
• During this time, the eastern end of the Tethys
  Sea
  – 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
    landmass
    Paleogeography of the World
• During the Late Cretaceous Period
        Higher Heat Flow Caused
    Sea Level Rise plate Tec Kicks into
               high Gear!
• 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 rapid expansion of oceanic ridges
 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
    area
  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
             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 atmosphere
     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
  climate through the end of the Cretaceous
     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
         The Mesozoic History
           of North America
• In North America, the beginning of the
  Mesozoic Era
  – 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
• Paleogeograph
  y 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
   Volcanic Island Arc at the Western
          Edge of the Craton
• A volcanic island arc system
  – that formed off the western edge of the craton
  – during the Permian
• was sutured to North America
  – sometime 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 Nevada,
  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
                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
• Like the Antler orogeny,
  – it resulted in the suturing of island-arc terranes
  – along the western edge of North America.
                  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
    boundary
      Cordilleran
      Mobile Belt




• Mesozoic orogenies
  – occurring in the
    Cordilleran mobile belt
           Cordilleran Orogeny

• Most of this Cordilleran orogenic activity
  – is related to the continued westward movement of
    the North American plate as it overrode the
    Farallon plate and its history is highly complex
                  Nevadan Orogeny
• The first phase of the Cordilleran orogeny,
   – the Nevadan orogeny,
   – began during the Mid to Late Jurassic
   – and continued into the Cretaceous
• During the Middle to Late Jurassic,
   – two subduction zones, dipping in opposite directions,
   – formed at the western margin of North America.
• As the North American plate moved westward,
   –   as a result of the opening of the Atlantic Ocean,
   –   it soon overrode the westerly subduction zone
   –   leaving only the easterly dipping subduction zone
   –   along its western periphery
                 Nevadan Orogeny
• As the easterly dipping ocean crust
   –   continued to be subducted,
   –   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
• At this time, the Franciscan Complex and Great
  Valley Group were deposited and deformed
     Batholiths




• Location of Jurassic and
  Cretaceous batholiths
  – in western North
    America
           Franciscan Complex
• The Franciscan Complex,
  – 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
    Cretaceous
• The various rock types include
  – graywacke, volcanic breccia, siltstone, black shale,
  – chert, pillow basalt, and blueschist metamorphic
    rocks
          Franciscan Complex

• The rock types suggest
  – that continental shelf, slope, and deep-sea
    environments
  – 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
• Bedded chert exposed in Marin County,
  California
• Most of the layers are about 5 cm thick.
           Great Valley Group
• The Franciscan Complex and Great Valley
  Group
  – that lies east of it
  – were both squeezed against the edge of the North
    American craton
  – as a result of subduction of the Farallon plate
  – beneath the North America plate.
• The Franciscan Complex and the Great Valley
  Group
  – are currently separated
  – by a major thrust fault
           Great Valley Group
• The Great Valley Group consists of
  – more than 16,000 m
  – of conglomerates, sandstones, siltstones, and
    shales
• 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
            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
    subduction,
  – 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
  – although it began in the Late Jurassic
  – and is associated with the tectonic activity
  – of the Nevadan orogeny
      Cordilleran
      Mobile Belt




• Mesozoic orogenies
  – occurring in the
    Cordilleran mobile belt
                     Thrust Faults
• Subduction of the Farallon plate
   – beneath the North American plate during this time
   – resulted in numerous overlapping,
   – low-angle thrust faults
• As compressional forces generated in the subduction
  zone
   –   were transmitted eastward,
   –   numerous blocks of older Paleozoic strata
   –   were thrust eastward
   –   on top of younger strata
• This deformation resulted in crustal shortening
   – and produced generally north-south-trending mountain
     ranges
                Sevier Orogeny
• Associated tectonic features
 – of the Late
   Cretaceous
   Sevier orogeny
 – caused by
   subduction of
   the Farallon
   plate
 – under the North
   American plate
      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
                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
    America
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
    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
         Black Shale Deposition
• Middle Cretaceous transgressions are marked
  – by widespread black shale deposition
  – within oceanic areas,
  – the shallow sea shelf areas,
  – and the continental regions
• that were inundated by the transgressions.
     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
    west
           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
  building,
  – these coarse clastic wedges of gravel and sand
  – prograded even further east
     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
    consequence
  – 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
                     Terranes
• Geologists now know that portions of many
  mountain systems
  – are composed of small accreted lithospheric blocks
  – 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
  rocks
  – 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 marginas 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
  margins
  – 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
                   Terranes

• 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 Paleogene 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 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 occurred
• 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
  domes
                Salt
• 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
    Europe,
  – which are composed of oolitic limonite and
    hematite,
  – and are important ores in France, Germany,
    Belgium, and Luxembourg
• In Great Britain, low-grade Jurassic iron ores
  – consist of oolitic siderite, which is an iron carbonate
• In Spain, Cretaceous rocks are the host rocks for
  iron minerals
                Kimberlite Pipes
• South Africa,
  – the world's leading producer of gem-quality
    diamonds and among the leaders in industrial
    diamond production, mines these minerals from
    conical igneous intrusions
     • called kimberlite pipes
  – Kimberlite pipes
     • are composed of dark gray or blue igneous rock known
       as kimberlite
    Cretaceous Kimberlite Pipes
• Diamonds,
     • which form at great depth where pressure and
       temperature are high,
  – are brought to the surface
     • during the explosive volcanism
     • that forms kimberlite pipes
• Although kimberlite pipes have formed
  throughout geologic time,
  – the most intense episode of such activity in South
    Africa and adjacent countries was during the
    Cretaceous Period
                  Mother Lode
• Emplacement of Triassic and Jurassic
  – diamond-bearing kimberlites also occurred in
    Siberia
• The mother lode
     • or source for the placer deposits mined during the
       California gold rush
  – is in Jurassic-age intrusive rocks of the Sierra
    Nevada
• Gold placers are also known in Cretaceous-age
  conglomerates
  – of the Klamath Mountains of California and Oregon
             Porphyry Copper
• Porphyry copper was originally named
  – for copper deposits in the western United States
    mined from porphyritic granodiorite, but the term
    now applies to large, low-grade copper deposits
    disseminated in a variety of rocks
• These porphyry copper deposits
  – are an excellent example of the relationship
    between convergent plate boundaries and the
    distribution, concentration, and exploitation of
    valuable metallic ores
      Origin of Porphyry Copper

• Magma generated by partial melting
  – of a subducting plate rises toward the surface,and
    as it cools, it precipitates and concentrates various
    metallic ores
• The world's largest copper deposits
  – were formed during the Mesozoic and Cenozoic in
    a belt along the western margins of North and
    South America
Plate Tectonics and the Distribution
        of Natural Resources
• Magma generated by subduction can
  create this activity – Bingham Mine in Utah is a
  – Example: copper      huge open-pit copper mine
    deposits in
    western Americas
          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 named, but interrelated, mountain-
    building events
  – that occurred in different regions at different times
  – but overlapped to some extent

				
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