Chapter 14 Mesozoic Earth History

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Chapter 14 Mesozoic Earth History

• Paleozoic Era Assembling Pangea
• Mesozoic Era Disassembling Pangea
• 245 to 66 million years ago breakup affected
  oceanic atmospheric circulation patterns, the
  distribution of land water, ecosystem
  distribution and terrestrial marine evolution.
• Major events of the Mesozoic Era
• Opening of Atlantic Ocean
• Uplift of Rocky Mountains
• Accumulation of salt deposits
• Emplacement of batholiths
• Biologic affects of plate tectonics

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During Triassic Pangea extended from pole to
pole, covered approx. 25 of Earths surface.
Panthalassa Ocean covered most of remainder.
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Distribution of land vs. water affects oceanic
and atmospheric wind patterns, which affects the
distribution of certain climatic conditions and
ecosystems. Large land areas arid climates
Past climate condi-tions preserved in certain
types of sedi-ments. Evaporites evaporation
pre-cipitation in enclosed basins. Red beds
sand dunes arid climates. Coal humid
climates.
Triassic Period
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Pangaea breakup 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.
Late Triassic/ Early Jurassic rift separation
of North America South America produced
Newark (graben) basins. Sediments basalts
Newark Supergroup
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Late Triassic/Early Jurassic - Salts accumulated
in the restricted, rift basins.
Low latitudes high temps, high evaporation,
little external drainage ideal conditions for
evaporite accumulation.
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• Jurassic Period Paleogeography

Initial opening of North Atlantic Ocean and Gulf
of Mexico/Caribbean Sea.
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North American sequences Orogenies of Meso-zoic
Era. After Paleozoic, most of craton was not
covered by epeiric seas.
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• The two cratonic Mesozoic sequences,
• the Absaroka sequence - Late Mississippian to
  Early Jurassic
• And the Zuni sequence - Early Jurassic to Early
  Paleocene
• Most Triassic Jurassic sedimentation occurred
  along the continental margins.
• East coast sedimentation Appalachians still
  fresh from late Paleozoic uplift. Upwelling
  magma (rifting of Pangea) further uplifted
  region. From Nova Scotia to Georgia, stretching
  of the continent opened graben basins. As
  rifting progressed, eroded materials infilled
  intermontaine basins and newly opening Atlantic
  Ocean basin.

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Large grabens half-grabens broke into smaller
ones as rifting progressed.
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• Exposed Newark Supergroup basins elongated
  lakes/ swamps, sediments poorly-sorted,
  continental detrital sediments (conglo-merates,
  sands, silts, shales with basalts basalt
  (diabase sills dikes).
• South Carolina Georgia basins are covered by
  Coastal Plain sediments

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Triassic Dinosaur tracks in mudstone/siltstone
Hartford, CT. Tracks are somewhat common,
bones are not.
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• As young Atlantic Ocean was widening, the cooling
  of the continental margin resulted in a gradual
  sinking. Continued weathering and erosion wore
  down the mountains and devel-oped a river system
  that delivered Jurassic-aged sediments into the
  new continental shelf system.
• Renewed uplift during the Cretaceous Period
  caused the continuation of continental shelf
  deposition, which gradually developed into a 3000
  meter thick wedge of sediments that gently dip
  toward the Atlantic Ocean.
• Georgia Cretaceous just south of Fall Line,
  mostly fluvial deltaic, with offshore marine
  downdip.

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• Gulf Coastal region Late Triassic/Early
  Jurassic opening as N. America S. America
  separated. Restricted basins warm climate
  evaporation. As basin widened, salts were
  covered by normal marine sediments. Weight of
  overlying sediments

caused salt beds to flow and form rising
diapirs of salt during Tertiary Period.
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• Cordilleran margin unlike the Appalachian
  margin, the Cordilleran Mesozoic history involves
  the interaction between the continental margin
  and the subducting Farallon Plate.
• This orogenic activity progressively affected the
  trench and continental slope, the continental
  shelf, and the cratonic margin, causing a
  thickening of the continental crust.
• Late Permian/Early Triassic Sonoman Orogeny
  subduction of an oceanic plate beneath the island
  arc and the thrusting of oceanic and island arc
  rocks eastward against the craton margin, the
  orogeny culminated with the collision of the
  island arc the continent.

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Jurassic Period after collision between island
arc continent, Cordil-leran margin became a
continental arc.
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• After the Sonoman Orogeny

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Franciscan complex a Late Jurassic/Early
Cretaceous chaotic mixture of graywacke, volcanic
breccia, siltstone, black shale, chert,
pillow-basalt, and blueschist (a low temperature,
high pressure metamorphic rock) resulting from
the scraping-off of continental shelf, cont.
slope, and deep sea sediments from the Farallon
Plate.
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Franciscan complex shown in pink. Reconstruction
of depositional environment (below).
16,000 meters of K cong., ss, sh, siltstone
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Cordilleran Orogeny components Jurassic
Tertiary Periods Nevadan emplacements of large
granite batholiths, Sierra Nevada, Idaho, S.
California, Coast Ranges. Sevier Shallower
sub-duction angle igneous activity moves
eastward. Laramide Rocky Mts. east of
Sevier Orogeny Cretaceous Tertiary Periods
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Style of Sevier Orogeny deformation, Cordilleran
margin, North America Mesozoic Era
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Sevier Orogeny Keystone Fault, west of Las Vegas.
Base of dark rocks marks the trace of the fault
(p. 270, Fig. 14.16).
Paleozoic
Mesozoic
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Early Triassic sedi-mentation consisted of
shallow-water marine ss, sh, ls - continental
shelf deposits. Middle and Late Triassic,
regression continental sediments.
Fluvial sediments
Petrified Wood in fluvial, deltaic
sediments Coastal, tidal flat, deltaic deposits
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• Colorado Plateau Triassic Early Jurassic
  Periods
• Navaho Sandstone Jurassic eolian
• Kayenta Formation Triassic fluvial. Mostly gray
  and red sandstone.
• Wingate Sandstone Triassic eolian. Brilliant red
  in color.
• Chinle Formation Fluvial shale. Dark colored.
  1,200 feet thick in parts of Arizona. Triassic
  period.
• Moenkopi Formation Permian-Triassic fluvial,
  deltaic, tidal flat. Topmost layer of the Grand
  Canyon. Made of shale, or hardened mud of
  floodwaters. Also known as "Chocolate Cliffs.
• Five Canyons strata http//sci2k.net/fivecanstrat
  a.html

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Zion National Park
Navajo Ss
Kayenta Fm.
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Cross-bedded, Jurassic Navajo Sandstone, Utah
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Middle Jurassic Sundance Sea
Late Jurassic Nevadan Orogeny caused a northward
regression of the Sundance Seaway. Seaway was
then covered by continental sediments incl.
Morrison Fm.
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Dinosaur Natl Monument tilted Morrison Fm.
sandstones, covered by shelter.
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Cretaceous Period map showing distribution of
continents, changed oceanic currents, Tethys
sea (between northern southern
hemisphere continents)
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As Pangea fragmentation continued in the
Creta-ceous, sea level rose re-opening interior
seaway.
The circulation of the sub-tropical Tethys Sea
and the interior seaway helped distribute heat to
northern latitudes. Western highlands contributed
most of the seaway clastics
Limestones chalks
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E-W Cross-section from Sevier Highlands through
Western Colorado. Mirror-image of Taconic/
Acadian Highlands Foreland Basin relationship
of eastern Craton (during the Paleozoic Era)
W
E
Foreland Basin
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Erosion of lightly compacted Cretaceous clays
yields a badlands-type topography.