Mesozoic Geology

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Mesozoic Geology
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Introduction

• The Mesozoic began 248 mya and ended 65 mya
• Three periods - Triassic, Jurassic, Cretaceous
• breakup of Pangaea was the major geologic event
• tectonism and sedimentation are used to classify
  the Mesozoic in N. America
• Note the overlap in three styles of Cordilleran
  Orogeny

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Tectonism and Sedimentation
Seaway drains
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1. The Breakup of Pangaea

• The movement of continents during and after the
  breakup affected global climate and oceanic
  regimes as well as that of individual continents
• ocean basins were created or closed before new
  mountain ranges were built
• sea-level changes

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Pangaea - Early Triassic
Pole to pole and straddled equator Panthalassa
Ocean E. coast indent is Tethys Sea northern
coast was the southern coastline of
EurAsia Southern coast N coasts of Ind Arabia,
Australia Many mountain ranges topography
controls climates sedimentation
Panthalassa
Tethys
Panthalassa
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Late Triassic Rifting E Orogeny W
We will consider mostly North America for this
lecture
Orogeny
Rift
Better look at Tethys
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Pangaea Early Jurassic
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E Jurassic Atlantic Rift Shallow
Note offshore Terranes
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E Jurassic Another Look
Orogeny
New Sea
Wrangellia
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Pangaea Jurassic
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Late Jurassic Early Cretaceous
Atlantic Connected with Tethys Africa rotation
closes Tethys
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Tethys
Atlantic
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Late K Epeiric Sea until 70 mya
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Mesozoic Global Climates

• Carbonates (for example the stable isotope index
  d13C) reveal large concentrations of carbon
  dioxide present in the Mesozoic atmosphere.
• This suggests a greenhouse climate.
• No glaciers, no coal, so CO2 abundant.
• Greenhouse gasses pass sunlight which hits the
  land and sea. Re-radiate heat (IR)
• Greenhouse gasses hold the heat, not lost to
  space as quickly. Warmer equilibrium.

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Global Climates in the Mesozoic

• Mesozoic climates were more equable than today,
  lacked the strong north-south climate zones.
• Mesozoic plant fossils indicate subtropical
  conditions in high latitude locations
• Seasonal differences were monsoonal

Cycads
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Next Mesozoic Tectonics NA

• Cretaceous global rise in sea level until 75
  -70 mya, vast MOR
• Jurassic
• Atlantic opens E,
• began building the Cordillera W,
• Gulf of Mexico begins to form and experiences
  evaporite deposition
• Late Triassic Begin rifting in East

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Late Triassic Rifting opens the Atlantic

• The Newark Supergroup documents the rifting of
  Pangaea to form the Atlantic
• Early Triassic saw coarse detrital sediments
  deposited from the erosion of Appalachian
  highlands
• fault-block basins developed as N. America
  separated from Africa and filled with nonmarine
  sediment plus dikes and sills
• eroded to a flat plain by the Cretaceous

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Mesozoic rift basins
Kean University
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Structure of the Newark basin
Note how faulting follows sedimentation
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Lake cycles, East Berlin formation
Alternating wet and dry climate due 21000y
Milankovitch cycle of tilt axis wobble Also
100,000 year cycles due to orbit eccentricity
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E. Jurassic Gulf Coast Evaporites
200 mya is just outside our door
Restricted Basin Lots of evaporation
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Gulf Coastal Region

• First, as continents separate, restricted basin,
  thick evaporites formed in the Gulf
• Normal marine deposition returned to the Gulf by
  Late Jurassic, with transgressions and
  regressions
• thousand of meters of sediments were deposited

Does this cross-section show a transgression or
regression?
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Gulf Coast continental margin
Rising Salt Domes
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http//www-erl.mit.edu/jfrank/pubBioPage/work/lu0
6_timeReversal.pdf
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Discussion Petroleum exploration around salt
domes
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Next Western North AmericaTectonics

• Building the western margin of North America and
  the Cordillera

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Western Region

• Cordilleran Orogeny
• Laramide - built the present day Rockies
  K-Tertiary
• Sevier J-K thrust faulting to the east
• Nevadan - Jurassic batholith intrusion in the
  Sierra Nevada and elsewhere on the western edge

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Displaced terranes Western Cordillera
These terranes overlap in age but have different
rock types, paleolatitudes and fossils. However,
we can deduce when they accreted from this
map. Arrange the following terranes by oldest
to youngest time of accretion onto the west
coast Alexander, Cache Creek, Chugach, Stikine,
Taku, Tracy Arm, Wrangellia,
Details, but you don't need them to do this
problem
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Western Margin during Orogens
North America drifting west due opening of
Atlantic
Westward subduction zones stopped when
continental crust arrived.
Late Triassic on, eastward subduction of Farallon
oceanic crust continues Cordilleran Orogeny Late
J Early K Nevadan Batholiths
Remember the late Permian Sonoma? It continued
into the Early Triassic
Nevadan Orogeny east subduction Farallon
Sonomia docking Late Pm Early Triassic
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Sierra Nevada Mountains
Nevadan Orogeny Subduction formed batholith
cores of continental volcanic arc once as tall
as Andes
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Mesozoic orogenic events
Thin-skinned tectonics
K-T Laramide Continental Overide Bouyant
Subduction
Cretaceous Sevier Wrangellia docking? Later moved
by transform fault?
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Buoyant Subduction Laramide Orogeny
Vertical block uplift
Normal, thin-skinned
Now we understand weird looking Tetons
Approaching Continent pushes accretionary wedge
sediments into forearc sediments
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Sevier thin-skinned deformation
Using the layer colored sky blue, look at the
faults. Is the hanging wall mostly up or down?
What kind of faults are these?
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Sevier thrust belt
Precambrian and/or Paleozoic Sediments thrust
over younger Mesozoic rocks
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lets look down here
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Look in detail at western plate margin
This area has much simpler geology
Franciscan Range, Great Valley Group, and Sierra
Nevada Volcanics and Plutonics
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Next Mesozoic Sedimentation on the Craton

• Cretaceous
• extensive marine deposition, thin to the east
• Jurassic
• clean cross-bedded sandstones
• marine sediments in the Sundance Sea
• Triassic
• shallow-water marine clastics
• red beds

Foreland Basin!
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North America - Triassic
Marine deposition limited to western margin
Volcanic Arc sends frequent ashfalls eastward
Newark
Pollen similar
Chinle
Note Equator
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Late Triassic Chinle Fm.
Mudstones and Sandstones of stream deposits,
volcanic ash, with fossil trees (the Petrified
Forest!) Texas, New Mexico, northern Arizona,
Nevada, Utah, and western Colorado Pollen
studies show that the Chinle is the same age as
early Newark Supergroup
http//en.wikipedia.org/wiki/Petrified_Forest_Nati
onal_Park
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Triassic caliche paleosol- Nova Sc.
Source of carbonates for d13C measurements.
Results suggest high CO2 in atmosphere
Similar in Newark Supergroup
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North America - Jurassic period
Dry region in the rain shadow of the beginning
Nevadans
Zuni Transgression
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Sedimentation
Seaway drains
Evaporites
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Jurassic Eolian sandstone
Navaho SS, S. Utah
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Jurassic Morrison Formation
http//rainbow.ldgo.columbia.edu/courses/v1001/mor
isson14.html
Paul Olsen's Dinosaur Course
Stream Deposits, huge sauropods Apatosaurus, also
Stegosaurus, carnivore Allosaurus
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Fossils of Jurassic dinosaurs
Morrison Formation sandstones, DNM, Vernal, Utah
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Late Cretaceous really big epeiric sea
http//www.blm.gov/ak/ak930/cultrl.html
Dinosaurs on the North Slope Scroll down, open
Alaskas Jurassic Park
Land
Land
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Did the Sevier Orogenic Belt form before or after
the Navaho SS, lower left?
Did the Sevier Orogenic Belt form before or after
the Fox Hills SS, upper right?
Western Interior Seaway Regression
Western Interior Seaway Transgression
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Dakota Sandstone
Early Cretaceous shallow sea sediments gently
folded by Sevier Orogeny.
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Then, at 75-70 my, Regression
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In Montana the sequence is similar. Above the
marine Pierre Shale (ammonites) and Claggett
Sandstone (nearshore and beach) is the Late
Cretaceous Judith River Fm. containing dinosaur
bones and conifers in stream deposits. Is this
sequence a transgression or a regression?
Western Interior Seaway Regression
Western Interior Seaway Transgression
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75 mya Regression
Mesa Verde Sandstones over Mancos Shale
Coarsening Upward
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K-T Boundary
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End of Mesozoic Geology