Early Paleozoic Earth History

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Chapter 10
Early Paleozoic Earth History
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The First Geologic Map

• William Smith,
• a canal builder, published the first geologic map
• on August 1, 1815

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Paleozoic History

• The Paleozoic history of continents
• major mountain-building activity along
  continental margins
• numerous shallow-water marine
• transgressions and regressions over their
  interiors
• These transgressions and regressions
• were caused by global changes in sea level
• that most probably were related
• to plate activity and glaciation

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Continental Architecture

• Cratons are the relatively stable
• and immobile parts of continents
• and form the foundation upon which
• Phanerozoic sediments were deposited
• Cratons typically consist of two parts
• a shield
• and a platform

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Epeiric Seas

• The transgressing and regressing shallow seas
• called epeiric seas
• were a common feature of Paleozoic
• Continental glaciation
• as well as plate movement
• caused changes in sea level
• and were responsible for the advance and retreat
• of the seas in which the sediments were deposited

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Mobile Belts

• Mobile belts are elongated areas of mountain
  building activity orogenic activity
• along the margins of continents
• where sediments are deposited in the relatively
  shallow waters of the continental shelf
• and the deeper waters at the base of the
  continental slope
• During plate convergence along these margins,
• the sediments are deformed
• and intruded by magma
• creating mountain ranges

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Paleogeographic Maps

• Geologists use
• paleoclimatic data
• paleomagnetic data
• paleontologic data
• sedimentologic data
• stratigraphic data
• tectonic data

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Six Major Paleozoic Continents

• At the beginning of the Paleozoic, six major
  continents were present including
• Baltica - Russia west of the Ural Mountains and
  the major part of northern Europe
• Gondwana - Africa, Antarctica, Australia,
  Florida, India, Madagascar, and parts of the
  Middle East and southern Europe
• Laurentia - most of present North America,
  Greenland, northwestern Ireland, and Scotland

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Six Major Paleozoic Continents (others)

• China - a complex area consisting of at least
  three Paleozoic continents that were not widely
  separated and are here considered to include
  China, Indochina, and the Malay Peninsula
• Kazakhstan - a triangular continent centered on
  Kazakhstan, but considered by some to be an
  extension of the Paleozoic Siberian continent
• and Siberia - Russia east of the Ural Mountains
  and Asia north of Kazakhstan and south Mongolia
• Besides these large landmasses, geologists have
  also identified
• numerous small microcontinents
• and island arcs associated with various
  microplates

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Paleogeography of the World

• For the Late Cambrian Period

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Paleogeography of the World

• For the Late Ordovician Period

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Paleogeography of the World

• For the Middle Silurian Period

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Early Paleozoic Evolution of North America

• The geologic history of the North American craton
  may be divide into two parts
• stable continental interior over which epeiric
  seas transgressed and regressed
• mobile belts where mountain building occurred

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Cratonic Sequences of N. America

• Cordilleraorogenies

• Appalachian oro-genies

• White areas represent sequences of rocks That
  are separated by large-scale unconformities shown
  in brown

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Cratonic Sequence

• A cratonic sequence is
• a large-scale lithostratigraphic unit
• representing a major transgressive-regressive
  cycle
• bounded by cratonwide unconformities

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The Sauk Sequence

• Rocks of the Sauk Sequence
• during the Neoproterozoic-Early Ordovician
• record the first major transgression onto the
  North American craton
• Deposition of marine sediments
• was limited to the passive shelf areas of the
• Appalachian and Cordilleran borders of the craton
  
• The craton itself was above sea level
• and experiencing extensive weathering and erosion
  

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• White areas sequences of rocks

• Sauk sequence

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The Sauk SequenceMiddle Cambrian Period

• North America was located in a tropical climate
  at this time
• there is no evidence of any terrestrial
  vegetation, NO plants!
• Rapid weathering and erosion of the exposed
  Precambrian basement rocks
• the transgressive phase of the Sauk
• began with epeiric seas encroaching over the
  craton

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Transcontinental Arch

• By the Late Cambrian,
• the epeiric seas had covered most of North
  America,
• leaving above sea level only
• a portion of the Canadian Shield
• and a few large islands
• These islands,
• collectively named the Transcontinental Arch,
• extended from New Mexico
• to Minnesota and the Lake Superior region

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Cambrian Paleogeography of North America

• During this time North America straddled the
  equator
• Trans-continental Arch

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Sauk Carbonates

• Many of the Sauk carbonates (limestones) are
• bioclastic
• composed of fragments of organic remains
• contain stromatolites,
• or have oolitic textures
• contain small, spherical calcium carbonate grains
• Such sedimentary structures and textures
• indicate shallow-water deposition

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A Transgressive Facies Model

• Sediments become finer away from land
• coarse detrital sediments are typically deposited
  in the nearshore environment,
• and finer-grained sediments are deposited in the
  offshore environment
• Carbonates form farthest from land in the marine
  environment beyond the reach of detrital sediments

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A Transgressive Facies Model

• Recall that facies are sediments
• that represent a particular environment
• During a transgression, the coarse (sandstone),
• fine (shale) and carbonate (limestone) facies
• migrate in a landward direction

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The Cambrian of the Grand Canyon Region

• This region provides an excellent example
• of sedimentation patterns of a transgressing sea
  
• The region of the Grand Canyon occupied
• the western margin of the craton during Sauk
  time,
• a passive shelf
• During Neoproterozoic and Early Cambrian time,
• most of the craton was above sea level
• deposition of marine sediments
• was mainly restricted to the margins of the
  craton
• on continental shelves and slopes

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Transgression

• A transgression covered
• the Grand Canyon region.
• The Tapeats Sandstone represents the shoreline
  depositsare clean, well-sorted sands
• of the type one would find on a beach today
• As the transgression continued into the Middle
  Cambrian,
• muds of the Bright Angle Shale
• were deposited over the Tapeats Sandstone

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Continued Transgression

• The Sauk Sea had transgressed so far onto the
  craton
• by the Late Cambrian that
• in the Grand Canyon region
• carbonates of the Muav Limestone were being
  deposited over the Bright Angel Shale
• This vertical succession of
• sandstone (Tapeats)
• shale (Bright Angel)
• and limestone (Muav)
• forms a typical transgressive sequence

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Cambrian Transgression

• Cambrian strata exposed in the Grand Canyon

• The three formations exposed
• along the Bright Angel Trail, Grand Canyon Arizona

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Cambrian Transgression

• Cambrian strata exposed in the Grand Canyon
• Observe the time transgressive nature of the
  three formations

• The three formations exposed
• along the Bright Angel Trail, Grand Canyon Arizona

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Upper Cambrian Sandstone

• Outcrop of cross-bedded Upper Cambrian sandstone
  in the Dells area of Wisconsin

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Regression and Unconformity

• As the Sauk Sea regressed
• from the craton during the Early Ordovician,
• it revealed a landscape of low relief
• The rocks exposed were predominately
• limestones and dolostones
• that experienced deep and extensive erosion
• because North America was still located in a
  tropical environment
• The resulting cratonwide unconformity
• marks the boundary between the Sauk
• and Tippecanoe sequences

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Cratonic Sequences of N. America

• White areas sequences of rocks

• brown areas large-scale uncon-formities

• Regression

• Tippecanoe sequence

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The Tippecanoe Sequence

• A transgressing sea deposited the Tippecanoe
  sequence over most of the craton
• Middle Ordovician-Early Devonian
• Like the Sauk sequence, this major transgression
  deposited clean, well-sorted quartz sands
• The Tippecanoe basal rock is the St. Peter
  Sandstone,
• an almost pure quartz sandstone used in
  manufacturing glass

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Ordovician Period

• Paleo-geography of North America
• showing change in the position of the the equator
• The continent
• was rotating counter-clockwise

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Transgression of the Tippecanoe Sea

• Resulted in deposition of
• the St. Peter Sandstone
• Middle Ordovician
• over a large area of the craton

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St. Peter Sandstone

• Outcrop of St. Peter Sandstone in Governor Dodge
  State Park, Wisconsin

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The Tippecanoe Sequence

• The Tippecanoe basal sandstones were followed by
  widespread carbonate deposition
• The limestones were generally the result of
  deposition
• by calcium carbonate-secreting organisms such
  as
• corals,
• brachiopods,
• stromatoporoids,
• and bryozoans

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Tippecanoe Reefs and Evaporites

• Organic reefs are limestone structures
• constructed by living organisms,
• some of which contribute skeletal materials to
  the reef framework
• Today, corals, and calcareous algae
• are the most prominent reef builders,
• but in the geologic past other organisms
• played a major role in reef building
• Reefs appear to have occupied
• the same ecological niche in the geological past
  as today

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Modern Reef Requirements

• present-day reefs are confined
• To between 30 degrees north and south of the
  equator
• Corals,
• the major reef-building organisms today,
• require warm, clear, shallow water
• of normal salinity for optimal growth

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Present-Day Reef Community

• with reef-building organisms

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Reef Environments

• Block diagram of a reef showing the various
  environments within the reef complex

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Michigan Basin Evaporites

• The Middle Silurian rocks of the present-day
  Great Lakes region Tippecanoe sequence
• are reef and evaporite deposits
• The most significant structure in the region
• the Michigan Basin
• is a broad, circular basin surrounded by large
  barrier reefs
• These reefs contributed to increasingly
  restricted circulation
• and the precipitation of Upper Silurian
  evaporites within the basin

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Silurian Period

• Paleogeography of North America during the
  Silurian Period
• Reefs developed in the Michigan, Ohio, and
  Indiana-Illinois-Kentucky areas

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Tippecanoe Regression and Evaporites

• As the Tippecanoe Sea gradually regressed
• from the craton during the Late Silurian,
• precipitation of evaporite minerals occurred in
  the Michigan Basin
• approximately 1500 m of sediments were deposited,
  
• nearly half of which are halite and anhydrite
  (gypsum)

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Origin of Thick Evaporites(Gypsum, Halite)

• How did such thick sequences of evaporites
  accumulate?
• 1. When sea level dropped, the tops of the
  barrier reefs were as high as or above sea level,
  
• thus preventing the influx of new seawater into
  the basin
• Evaporation of the basinal seawater would result
  in the precipitation of salts
• 2. Alternatively, the reefs grew upward so close
  to sea level
• that they formed a sill or barrier that
  eliminated interior circulation

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Silled Basin Model

• Silled Basin Model for evaporite sedimentation by
  direct precipitation from seawater
• Vertical scale is greatly exaggerated

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Basin Brines

• Because North America was still near the equator
  during the Silurian Period,
• temperatures were probably high

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Reefs in a Highly Saline Environ-ment?

• Organisms constructing reefs could not have lived
  in such a highly saline environ-ment

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No Model Is Perfect

• How then, can such contradictory features be
  explained?
• Numerous models have been proposed, ranging from
• cessation of reef growth followed by evaporite
  deposition,
• to alternation of reef growth and evaporite
  deposition
• no model yet proposed completely explains
• various reef, carbonate, and evaporite facies

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The Appalachian Mobile Belt

• where the first Phanerozoic orogeny
• began during the Middle Ordovician
• How would a mountain range influence
• the climate and sedimentary history of the craton?

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Mountain Building

• Global tectonic regime
• that sutured the continents together, forming
  Pangaea by the end of the Paleozoic
• The Appalachian region
• throughout Sauk time,
• was a broad, passive, continental margin
• Sandstone shale - carbonate

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Iapetus Ocean

• Iapetus Ocean was widening
• as a result of movement
• along a divergent plate boundary
• Beginning with the subduction of the Iapetus
  plate beneath Laurentia
• which was an oceanic-continent convergent plate
  boundary
• the Appalachian mobile belt was born

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Appalachian Mobile Belt

• Evolution of the Appalachian mobile belt
• opening of Iapetus Ocean

• with passive continental margins
• and large carbonate platforms

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The Taconic Orogeny

• The resulting Taconic orogeny,
• named after present-day Taconic Mountains of
• eastern New York,
• central Massachusetts,
• and Vermont
• was the first of several orogenies
• to affect the Appalachian region

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Eastern Sediment Source

• The subduction of the Iapetus plate beneath
  Laurentia
• resulted in volcanism
• and downwarping of the carbonate platform
• Throughout the Appalachian mobile belt,
• indications that these deposits were derived from
  the east, come from
• facies patterns,
• paleocurrents,
• and sedimentary structures
• The sediment originated where
• the Taconic Highlands
• and associated volcanoes were rising

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Appalachian Mobile Belt

• Middle Ordovician transition to convergence
  resulted in orogenic activity

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Queenston Delta Clastic Wedge

• The final piece of evidence
• for the Taconic orogeny is
• the development of a large clastic wedge,
• an extensive accumulation of mostly detrital
  sediments
• were deposited adjacent to an uplifted area
• and become thinner and finer grained away from
  the source area,
• eventually grading into the carbonate cratonic
  facies
• The clastic wedge resulting from the erosion
• of the Taconic Highlands is referred
• to as the Queenston Delta

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Queenston Delta Clastic Wedge

• Queenston Delta clastic wedge

• Taconic Highlands

• coarse-grained detrital sediments near the
  highlands
• thins laterally into finer-grained sediments on
  the craton

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A European Orogeny

• The Taconic orogeny
• marked the first pulse of mountain building in
  the Appalachian mobile belt
• and was a response to the subduction taking place
  beneath the east coast of Laurentia
• As the Iapetus Ocean narrowed and closed,
• another orogeny occurred in Europe during the
  Silurian

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Caledonian Orogeny

• The Caledonian orogeny was essentially a mirror
  image of
• the Taconic orogeny and the Acadian orogeny
• and was part of the global mountain-building
  episode
• that occurred during the Paleozoic Era
• Even though the Caledonian orogeny
• occurred during Tippecanoe time,
• we will discuss it with the Acadian orogeny
• because the two are intimately related

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Caledonian Orogeny

• The transition to convergence resulted in
  orogenic activity in North America and Europe

• Caledonian Orogeny
• was a mirror image of the Taconic Orogeny