The Mesozoic Era

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The Mesozoic Era

• CHAPTER 11

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The Mesozoic (245 to 65 Mya)

• Beginning and ending with extinctions
• Spans Three Periods
• Triassic 245 to 208 m.y.
• Jurassic 208 to 188 m.y.
• Cretaceous 144 to 65 m.y.
• Supercontinent of Pangaea rifted apart over a
  span of 150 million years.

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Global paleogeography near the end of the
Paleozoic Era
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Breakup of Pangaea four stages (three during
Mesozoic)

• Stage One Triassic
• Rifting and volcanism, normal faulting
• tensional stresses separated N. America from
  Gondwanaland
• similarly, Mexico from S. America
• similarly, eastern N. America from N. Africa
• Sea-floor generation during opening of oceans
  (basaltic volcanism)

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Triassic Paleogeography
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Breakup of Pangaea (cont)

• Stage Two Triassic-Jurassic
• Rifting of narrow oceans between S. Africa and
  Antarctica, Africa and India
• Massive outpouring of basaltic lavas (7 million
  km2)

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Jurassic Paleogeography
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Breakup of Pangaea (cont)

• Stage Three Jurassic-Cretaceous
• Atlantic Ocean rift extended northward
• Clockwise rotation of Eurasia
• Closing of eastern Tethys Sea (pre-Mediterranean)
• S. America-Africa split apart
• Australia-Antarctica remained intact
• Eastern N. America-Greenland remained intact

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Cretaceous Paleogeography
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Breakup of Pangaea (cont)

• Stage Four post-Mesozoic
• Complete N. America-Eurasian split
• Antarctica-Australia split

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Triassic and Jurassic (eastern and southern areas)

• Normal fault-bounded basins developed due to
  rifting Nova Scotia to North Carolina
• troughs filled with terrestrial sediments and
  volcanics
• Newark Group (Upper Triassic-Lower Jurassic)
• Palisades basalts of NJ and NY (190 m.y. ago)

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Figure 11-3 (p. 384) Generalized
paleogeographic map for the Triassic of North
America.
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Palisades Sill
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Development of Gulf of Mexico

• occupied areas opening south of
  Appalachian-Ouachita folded mountains
• filled with Upper Triassic-Lower Jurassic salts
  and evaporites (indicating aridity) over 1000 m
  deposited origin of Gulf coast salt domes of
  today

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Figure 11-7 (p. 387) Generalized
paleogeographic map for the Jurassic of North
America.
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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

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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

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Cretaceous (eastern and southern areas)

• Flooding of coastal lowlands due to high sea
  levels
• a. Atlantic and Gulf Coastal Plains inundated as
  they acted as subsiding shelves at this time
• b. thick deposits of deltas, barrier islands,
  shelves, reefs, etc.formed
• c. Florida shallow submarine bank for limestones
• d. reefs made of rudistid bivalves rimmed Gulf
  Coastal area duringthe Early Cretaceous
• e. extensive chalk deposits of Cretaceous sea due
  to massive production of microscopic calcareous
  plankton (coccoliths) creta chalk
• Rifting and ocean opening on eastern side led to
  closure and compression on the western side of
  continent subduction resulted.

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Figure 11-12 (p. 392) Generalized
paleogeographic map for the Cretaceous of North
America.
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Triassic--Western North America

• Steeply dipping subduction zone
• Volcanic arcs and micro-continents carried to
  western margin (displaced or allochthonous
  terranesas many as 50 now known)
• Massive accretion by subduction (including
  volcanism), and tectonic accretion of displaced
  terranes
• Tectonic collage of displaced terrains may be 70
  of total western Cordilleran termed accretionary
  tectonics

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Map of the larger allochthonous (accreted)
terranes of western North America. The rocks in
these terranes contain rocks of Paleozoic age, or
older. The pink areas may be displaced areas of
the North American continent, but the green areas
probably originated as parts of other continents.
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Triassic--Western North America

• Sonoma Orogeny Permian-Triassic, Nevada
• island arc collided with west coast
• then a west-dipping subduction zone
• added 300 km new area to west

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Jurassic-Early Tertiary-Western N. America

• Nevadan Orogeny
• Formation of convergent mélange deposits
• Great volumes of granodiorite intruded Sierra
  Nevada, Idaho, and Coast Range batholiths
• Sevier Orogeny
• basement-involved tectonics multiple imbricated
  thrust faults (low-angle décollement structures)
• mainly seen in NV and UT, also in MT, BC, Alberta
• most famous thrust fault Lewis Thrust (65 km
  displacement)
• Laramide Oroeny
• Deformation more easterly
• Created original Rocky Mountain Landscape
• New Mexico, Colorado, Wyoming Mountain

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Figure 11-22 (p. 396) Mesozoic batholiths in
west-central North America.
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Jurassic Sedimentation

• Navajo Sandstone (Lower Jurassic, MT, WY, NV,
  Alberta) clean recycled eolian sands deposited
  in coastal dune and shoreline environments
• Sundance Formation (Middle) Jurassic, famous for
  fossil reptiles) deposits of the Sundance Sea
• Morrison Formation (Upper Jurassic, famous for
  dinosaurs) swampy plain deposits formed as
  Sundance Sea regressed upon rising of Cordilleran
  highlands to the west

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Figure 11-26 (p. 398) Paleogeographic map for
the early Jurassic of the western United States,
showing general extent of sea and land as well as
paleolatitudes. (From Stanley et al. 1971. Bull.
Am. Assoc. Petrol. Geol. 55(1) 13.)
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Figure 11-27 (p. 398) Region in the western
North America inundated by the Middle Jurassic
Sundance Sea. (Land areas are shown in tan,
marine areas in blue.)
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Cretaceous Sedimentation

• Early Cretaceous Seaway marine intrusions
  leaving deposits south from Arctic Ocean and
  north from Gulf of Mexico, dry land between two
  seaways (UT and CO), seas withdrew during Middle
  Cretaceous regression
• Late Cretaceous Seaway greatest of marine
  intrusions (transgressions) connected Gulf of
  Mexico and Arctic Ocean via epicontinental seaway
  (Western Interior Seaway) flooded area
  foreland basin