Chapter 10 Early Paleozoic Earth History Cambrian Silurian Periods

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Chapter 10 - Early Paleozoic Earth
History(Cambrian Silurian Periods)
(Modified from Hatcher et al. (1990), Steltenpohl
et al. (1995), and Hooper Hatcher (1988).)
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• The Paleozoic history of most continents involves
  major mountain-building activity along their
  margins (mobile belts) numerous shallow-water
  marine transgressions and regressions over their
  interiors.
• These transgressions and regressions were caused
  by global changes in sea level, most likely
  related to plate activity and glaciation.
• Most of the geologic time scale was developed in
  Europe, sedimentary record in North America was a
  little different, so we will be looking at the
  major Transgressive-Regressive sequences of the
  Paleozoic Era and how they affected life.

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• With the Late Proterozoic breakup of Rodinia and
  Pannotia 6 continents existed in early
  Paleozoic. Each continent composed of craton and
  one or more mobile belts.
• Craton composed of shield and platform upon which
  the Paleozoic sediments were deposited. Cratons
  were built by tectonic activity during the
  Precambrian, but remained stable during the
  Paleozoic.
• The transgressing and regressing shallow seas
  (epeiric seas) were a common feature of most
  Paleozoic cratonic histories. Flooding occurred
  during times of higher activity at rift zones,
  shrinkage of global ice sheets, and/or
  continental sinkage following rifting.

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Canadian shield not covered during
Paleozoic, re-mainder of craton (light brown) was
periodically cover-ed by epeiric (shallow,
inland) seas. Green (basins) yellow (domes)
local areas of gentle warpage of platform
sedimentary rocks.
Appalachian Basin
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• Some of the (yellow) topographic highs were
  exposed as islands during the Paleozoic and
  supplied clastic sediments to the surrounding
  areas.
• Mobile belts elongated areas of mountain
  building activity along the margins of
  conti-nents. Shallow continental shelf and
  deeper continental slope sediments were deformed
  (and intruded by magmas) during times of
  continental compression and collision.
• 4 North American mobile belts
• Franklin mobile belt
• Cordilleran mobile belt
• Ouachita mobile belt (Ark./Okla.)
• Appalachian mobile belt (SE E North America)

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• Historical Geology seeks to present snapshots
  of Earth history by way of Paleogeographic maps
  that show -
• 1) The distribution of land and sea
• 2) Possible climate regimes, and
• 3) Geographic features, e.g., mountain ranges,
  swamps, deltas, glaciers, etc..
• 4) Plate tectonic-related features distribution
  of volcanoes, shape of coastlines, sedimentation
  patterns, etc..
• Paleozoic paleogeographic reconstructions are
  based primarily on 1) Structural relationships 2)
  Climate-sensitive sediments such as red beds,
  evaporates, and coals, and 3) Distribution of
  plants and animals.

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• 1963 Laurence Sloss divided North American
  sedimentary rocks into 6 Cratonic sequences, 4 of
  which include the Paleozoic Era (slide 8 p.
  180).
• Sauk Sequence (Late Proterozoic Early
  Ordovician) marked by a steady rise in sea
  level and rapid weathering and erosion of exposed
  Precambrian due to tropical environment (slide 9)
  with no vegetative cover. Resulted in
  transgressive sand sequences being deposited on
  both sides of the continent.
• Tapeats SS Coronado SS (S. AZ) Bliss SS (TX)
• Arizona (Early Cambrian) eastward into West Texas
  (Early Ordovician) (slide 10).

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Sloss Sequences N. America
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• Cambrian
• Paleogeo-
• Graphic Map
• of Laurentia.
• Shows Equa-
• tor, Epeiric
• seas, Conti-
• nental
• Shelves,
• Exposed
• areas.

Counter-clockwise rotation to reach present
orientation.
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Cambrian transgressive sequence Grand Canyon
local source of shale. El Paso area shale is
missing no local source.
Bright Angel Shale Early Cambrian California
Middle Cambrian Grand Canyon. Muav Limestone
marks the top of the Sauk Sequence in the Grand
Canyon.
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East Coast Sauk Trans-gressive Sequence was
deposited over Grenville-age continental
crust. The end-of-Sauk regression exposed
Cambrian/Early Ordovician carbonates and
sandstones to erosion.
By the end of Middle Cambrian source of shale
deposition is drowned.
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• After regression of the
• Sauk Sea erosion,
• Tippecanoe Trans-
• gression began with
• the deposition of
• clean sandstones. St.
• Peter Sandstone
• best known of the
• Tippecanoe basal
• sandstones.

Tippecanoe (Ordovician) paleogeographic map.
Note rise of Taconic Highlands (discussed later).
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Central Kentucky/ Tennessee eastern craton
transition from carbonate to shale deposition.

• Tippecanoe deposition marked by widespread
  deposition of limestones in epeiric seas, due to
  lack of clastics from eroded landmasses. Shales
  in eastern portion of craton were derived from
  the rising eroding Taconic Highlands. Gray/
  light brown shales shallow marine. Red shales
  tidal flats alluvial plain.

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• By Tippecanoe time reef forming organisms
  (corals, calcareous algae, bryozoa, sponges,
  stomatoporoids) were more developed and
  colonized suitable areas of epeiric sea bottom.
• Most favorable conditions shallow, warm, clear
  water of normal salinity. Locations determined
  by bottom topography, seafloor subsidence, wind
  and wave action, interactions by different
  organisms. Barrier reefs form at the outer edge
  of continental shelves. Ex Great Barrier Reef
• As reefs are in tropical/sub-tropical regions, if
  reef inhibits water circulation in the backreef
  area, evaporation may produce layers of
  evaporites (salts) or carbonate/evaporite
  sequences.

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Typical Barrier Reef Complex
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During Silurian Period peak of Tippecanoe
Trans-gression covered all of craton, ex-cept
Taconic High-lands. Silurian alluvial
plain/tidal flat deposits include Red Mountain
Fm., Ringgold Roadcut Birmingham, AL.
Barrier reefs surround basin, Pinnacle reefs grow
w/in basin, p. 186.
Reef development surrounding Michigan Basin
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• The Taconic Orogeny
• The first Phanerozoic orogeny began during the
  Middle Ordovician Period, influenced the climate
  and sedimentation of the craton.
• During the Sauk Sequence, eastern margin was a
  passive margin, with a continental shelf east of
  the flooded craton.
• Debates exist over nature of event, thought to be
  a collision between an island arc or small
  con-tinent. Resulting in uplift of Taconic
  Highlands and downwarping and drowning of
  existing carbonate shelf. Carbonate deposition
  ceased during Middle Ordovician, replaced by
  orogeny-related deepwater shales, graywackes.

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Clastic wedge developed NW of Taconic
High-lands, tidal flat and alluvial/delta
sediments in-clude Red Mountain Fm. in NW Ga. and
Birmingham, AL.