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The Proterozoic: Dawn of a More Modern World


Chapter 9 The Proterozoic: Dawn of a More Modern World Proterozoic Eon 2.5 billion years to 542 million years ago Comprises 42% of Earth history Divided into three ... – PowerPoint PPT presentation

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Title: The Proterozoic: Dawn of a More Modern World

Chapter 9
  • The Proterozoic Dawn of a More Modern World

Proterozoic Eon
  • 2.5 billion years to 542 million years ago
  • Comprises 42 of Earth history
  • Divided into three eras
  • Paleoproterozoic Era (2.5 - 1.6 by ago)
  • Mesoproterozoic Era (1.6 to 1.0 by ago)
  • Neoproterozoic Era (1.0 by ago to the beginning
    of the Paleozoic, 542 my ago)

The Beginning of the Proterozoic Marks the
Beginning of
  • More modern style of plate tectonics
  • More modern style of sedimentation
  • More modern global climate with glaciations
  • Establishment of the beginnings of an oxygen-rich
  • Emergence of eukaryotes

Precambrian Provinces in North America
  • Precambrian provinces were welded (or sutured)
    together to form a large continent called
    Laurentia during the early Proterozoic.

Precambrian Provinces in North America
  • Oldest (Archean) rocks are shown in orange.
  • Younger (Proterozoic) rocks are shown in green.

Precambrian Provinces in North America
  • Suturing occurred along mountain belts or
  • Provinces were assembled by about 1.7 b.y. ago.
  • Laurentia continued to grow by accretion
    throughout the Proterozoic.

Proterozoic Plate Tectonics
  • Late in the Proterozoic, the continents became
    assembled into a supercontinent called Rodinia.

Proterozoic Sedimentation
  • Sedimentation on and around the craton consisted
    of shallow water clastic and carbonate sediments
    deposited on broad continental shelves and in
    epicontinental seas.

Proterozoic Climate
  • Proterozoic glaciations occurred during the
  • Paleoproterozoic, about 2.4-2.3 b.y. ago
    (Huronian glaciation)
  • Neoproterozoic, 850-600 m.y. ago (Varangian

  • Overview
  • of the
  • Precambrian

  • Overview of Proterozoic Events

Paleoproterozoic Era
  • The oldest part of the Proterozoic
  • Ranges from about 2.5 b.y. to 1.6 b.y.
  • Covers 900 million years

Major Events of the Paleoproterozoic
  1. Active plate tectonics
  2. Major mountain building on all major continents
  3. Earth's first glaciation
  4. Widespread volcanism (continental flood basalts)
  5. Rise in atmospheric oxygen (great oxidation

Major Events of the Paleoproterozoic
  1. Accumulation of high concentrations of organic
    matter in sediments (Shunga event) 2000 m.y. ago,
    and generation of petroleum
  2. Oldest known phosphorites and phosphate

  • Orogenic belts developed around margins of the
    Archean provinces.
  • Wopmay belt in NW Canada
  • Trans-Hudson belt, SW of Hudson Bay

Wopmay orogenic belt contains evidence of
  1. Rifting and opening of an ocean basin (with
    normal faults, continental sediments, and lava
  2. Sedimentation along new continental margins (with
    shallow marine quartz sandstones and carbonate
  3. Closure of the ocean basin (with deep water
    clastics overlain by deltaic and fluvial sands),
    followed by folding and faulting.

Wilson Cycle
  • This sequence of events in the Wopmay orogenic
    belt is called a Wilson Cycle, and is a result of
    plate tectonics.
  • Rifting and opening of an ocean basin
  • Sedimentation along new continental margins
  • Closure of the ocean basin
  • The sequence of events in the Wopmay belt is
    similar to that in the Paleozoic of the

Trans-Hudson orogenic belt
  • Trans-Hudson belt contains the sedimentary record
    of a Wilson Cycle, with evidence of
  • Rifting
  • Opening of an ocean basin
  • Deposition of sediment
  • Closure of the ocean basin along a subduction
    zone, associated with folding, metamorphism, and
    igneous intrusions.
  • This closure welded the Superior province to the
    Hearne and Wyoming provinces to the west.

Paleoproterozoic Glaciation - Earth's First Ice
  • A Paleoproterozoic ice age is recorded in rocks
    north of Lake Huron in southern Canada (called
    the Huronian glaciation).
  • Gowganda Formation.
  • Age of Huronian glaciation 2450-2220 m.y.
  • Apparent rapid onset of global glaciations from
    what had been relatively stable climatic

Evidence for glaciation includes
  • Mudstones with laminations or varves - fine
    laminations indicating seasonal deposition in
    lakes adjacent to ice sheets.
  • Glacial dropstones (dropped from melting
    icebergs) in varved sedimentary rocks.
  • Tillites or glacial diamictites (poorly sorted
    conglomerates of glacial debris).
  • Scratched and faceted cobbles and boulders in
    tillite, due to abrasion as ice moved.

Widespread Glaciation
  • Age of global glaciations 2.6 - 2.1 b.y. ago
    (2600-2100 m.y.).
  • Widespread glaciation at this time as indicated
    by glacial deposits found in
  • Europe
  • southern Africa
  • India

Banded iron formations and prokaryote fossils
  • Extensive banded iron formations (BIF's) on the
    western shores of Lake Superior, indicate that
    photosynthesis was occurring and oxygen was being

Banded iron formations and prokaryote fossils
  • Some BIF deposits are gt1000 m thick, and extend
    over 100 km.
  • Animikie Group.
  • Rich iron deposits were foundation of steel
    industry in Great Lakes region (Illinois,
    Indiana, Ohio, Pennsylvania).
  • Mining has declined because U.S. imports most of
    its iron ore and steel.

Banded iron formations and prokaryote fossils
  • The Gunflint Chert, within the BIF sequence,
    contains fossil remains of prokaryotic organisms,
    including cyanobacteria.Age 1.9 b.y.

Labrador Trough
  • East of the Superior province are rocks deposited
    on a continental shelf, slope, and rise.
  • Rocks are similar to those of the Wopmay orogenic
  • These rocks were folded, metamorphosed, and
    thrust-faulted during the Hudsonian orogeny,
    which separates the Paleoproterozoic from the

Mesoproterozoic Era
  • The Mesoproterozoic (or middle Proterozoic)
    ranges from about 1.6 b.y. - 1.0 b.y.

Highlights of the Mesoproterozoic
  • The Midcontinent rift, an abandoned oceanic rift
    in the Lake Superior region with massive basaltic
    lava flows
  • Copper mineralization in the Lake Superior region
  • Continental collisions producing the Grenville
    orogeny in eastern North America
  • The assembly of continents to form the
    supercontinent, Rodinia.

Midcontinent Rift and the Keweenawan Sequence
  • Midcontinent rift extends southward from Lake
    Superior region.
  • Overlies Archean crystalline basement rocks and
    Paleoproterozoic Animikian rocks (Animikie Group

Midcontinent Rift and the Keweenawan Sequence
  • Large volumes of basaltic rock indicate presence
    of an old abandoned rift zone called the
    Midcontinent rift.
  • This was the first stage of a Wilson Cycle.
  • Rift developed 1.2 b.y. - 1.0 b.y. ago.
  • Extended from Lake Superior to Kansas.
  • Rifting ceased before the rift reached the edge
    of the craton, or the eastern U.S. would have
    drifted away from the rest of North America.

Midcontinent Rift and the Keweenawan Sequence
  • The Keweenawan Sequence consists of
  • Clean quartz sandstones
  • Arkoses
  • Conglomerates
  • Basaltic lava flows more than 25,000 ft thick
    (nearly 5 mi) with native copper
  • Basaltic rock beneath the surface crystallized as
    the Duluth Gabbro, 8 mi thick and 100 mi wide.

Copper Mineralization
  • Native copper fills vesicles (gas bubbles) in the
    Keweenawan basalt, and joints and pore spaces in
    associated conglomerates.
  • Native Americans mined the copper as early as
    3000 BC.
  • Copper was mined extensively from 1850 to 1950,
    but copper production ceased in the 1970's.

Grenville Province and Grenville Orogeny
  • The Grenville province in eastern North America
    extends from northeastern Canada to Texas.

Grenville Province and Grenville Orogeny
  • Grenville rocks were originally sandstones and
    carbonate rocks.
  • Grenville Province was the last Precambrian
    province to experience a major orogeny.
  • Grenville orogeny 1.2 b.y. to 1.0 b.y. ago

Grenville Province and Grenville Orogeny
  • Orogeny occurred when Eastern North America
    (Laurentia) collided with western South America
  • Orogeny was associated with formation of the
    supercontinent, Rodinia.
  • Later, during the Paleozoic Era, Grenville rocks
    were metamorphosed and intruded during the three
    orogenies involved in the building of the

The Supercontinent, Rodinia
  • The supercontinent, Rodinia, as it appeared
    about 1.1 b.y. ago.The reddish band down the
    center of the globe is the location of
    continental collisions and orogeny, including the
    Grenville orogeny.

The Supercontinent, Rodinia
  • Rodinia formed as the continents collided during
    the Grenville Orogeny.
  • Rodinia persisted as a supercontinent for about
    350 million years.
  • It was surrounded by an ocean called Mirovia.

Rifting in Rodinia
  • Rodinia began to rift and break up about 750
    million years ago, forming the proto-Pacific
    Ocean, Panthalassa, along the western side of
    North America.

Rifting in Rodinia
  • An early failed attempt at rifting began in
    eastern North America about 760 m.y. ago, with
    the deposition of sediments of the Mount Rogers
    Formation in a fault-bounded rift valley.
  • Felsic and mafic volcanic rocks are interlayered
    with the sedimentary rocks of the Mount Rogers

Neoproterozoic Era
  • The Neoproterozoic (or new Proterozoic) ranges
    from about 1.0 b.y. to 0.542 b.y. (542 m.y.).

Highlights of the Neoproterozoic
  • Extensive continental glaciations
  • Sediments deposited in basins and shelf areas
    along the eastern edge of the North American
  • Most of these rocks were deformed during the
    Paleozoic orogenies.

Glacial deposits in the Neoproterozoic
  • Glacial deposits formed roughly 600 - 700 m.y.
  • Evidence for glaciation
  • Glacial striations (scratched and grooved pebbles
    and boulders)
  • Tillites (lithified, unsorted conglomerates and
    boulder beds) found nearly worldwide
  • Glacial dropstones (chunks of rocks released from
    melting icebergs)
  • Varved clays from glacial lakes

Rifting in Rodinia
  • Around 570 million years ago, rifting began
    again, and South America began to separate from
    North America, forming the Iapetus Ocean (or
    proto-Atlantic Ocean).
  • The rift ran along what is now the Blue Ridge
    province. Basaltic lava flows formed the Catoctin
  • As the Iapetus Ocean opened, sands and silts were
    deposited in the shelf areas.

Glacial deposits in the Neoproterozoic
  • This time is referred to as "snowball Earth
    because glacial deposits are so widespread.
  • Varangian glaciation (named after an area in
  • The late Proterozoic ice age lasted about 240

Plate Tectonics and Glaciation
  • Plate tectonics may have had a role in cooling
    the planet.
  • Continents were located around the equator about
    600 to 700 m.y. ago.
  • No tropical ocean.

Plate Tectonics and Glaciation
  • Heat lost by reflection from the rocks on the
    surface of the continents may have caused global
    cooling. (Land plants had not yet appeared.)
  • As continental glaciers and ice caps formed,
    reflectivity of snow and ice caused further
    temperature decrease.

Atmospheric Gases and Glaciation
  • Glaciation was associated with
  • Decrease in CO2 and
  • Increase in O2.
  • CO2 causes the greenhouse effect and global
    warming. Decrease in CO2 may have caused cooling.
  • Decrease in CO2 was probably caused by increase
    in the number of photosynthetic organisms
    (cyanobacteria, stromatolites).

Limestones and Glaciations
  • Limestones are associated with glacial deposits,
    which is unusual, since limestones generally form
    in warm seas, not cold ones.
  • Association of limestones with glacial deposits
    suggests that times of photosynthesis and CO2
    removal alternated with times of glaciation.
  • Limestones (made of CaCO3) are a storehouse of
    CO2, which was removed from the atmosphere.

Limestones and Glaciations
  • Glacial conditions may have inhibited
    photosynthesis by stromatolites.
  • As a result, CO2 may have accumulated
    periodically and triggered short episodes of
    global warming.
  • This produces the paradox of glaciers causing
    their own destruction.

Proterozoic Rocks South of the Canadian Shield
  • Extensive outcrops of
  • Precambrian rocks are
  • present in the
  • Canadian Shield.
  • Precambrian rocks are also present in other
  • including
  • Rocky Mountains
  • Colorado Plateau (Grand Canyon)

Events Recorded in Proterozoic Rocks
  1. Collision of an Archean terrane with volcanic
    island arc, 1.7 or 1.8 b.y.a. (Wyoming and
    western Colorado)
  2. Extensive magma intrusion in Mesoproterozoic,
    1.5-1.4 b.y.a. (California to Labrador)
  3. Widespread rifting
  4. Rifts with thick sequences of shallow water
    Neoproterozoic sedimentary rocks, 1.4 - 0.85
    b.y.a. Belt Supergroup (Glacier National Park,
    Montana, Idaho, and British Columbia).

Precambrian rocks of the Grand Canyon
  • Vishnu Schist metasediments and gneisses,
    intruded by Zoroaster Granite about 1.4 b.y. to
    1.3 b.y.a. during the Mazatzal orogeny.
  • Top of Vishnu Schist is an unconformity.

Precambrian rocks of the Grand Canyon
  • Grand Canyon Supergroup overlies unconformity.
    Neoproterozoic sandstones, siltstones, and
    shales. Correlates with Belt Supergroup.
  • Unconformably overlain by Cambrian rocks.

Proterozoic Life
Life at the beginning of the Proterozoic was
similar to that in the Archean
  1. Archaea in deep sea hydrothermal vents
  2. Planktonic prokaryotes floated in seas and lakes
  3. Anaerobic prokaryotes in oxygen-deficient
  4. Photosynthetic cyanobacteria (prokaryotes)
    constructed stromatolites (algal filaments)
  5. Eukaryotes (as indicated by molecular fossils)

Other forms of life appeared during the
  1. More diverse eukaryotes including acritarchs
  2. Metazoans or multicellular animals with soft
  3. Metazoans with tiny calcium carbonate tubes or
  4. Metazoans that left burrows in the sediment

Microfossils of the Gunflint Chert
  • First definitive Precambrian fossils to be
    discovered (in 1953) were in the 1.9 b.y. old
    Gunflint Chert, NW of Lake Superior

Microfossils of the Gunflint Chert
  • The fossils are well-preserved, abundant and
    diverse and include
  • String-like filaments
  • Spherical cells
  • Filaments with cells separated by septae
  • Finely separate forms resembling living algae
  • Star-like forms resembling living iron- and
    magnesium-reducing bacteria (Eoastrion)

Microfossils of the Gunflint Chert
  • A Eoastrion ( dawn star), probably iron- or
    magnesium-reducing bacteriaB Eosphaera, an
    organism or uncertain affinity, about 30
    micrometers in diameterC Animikiea (probably
    algae)D Kakabekia, an organism or uncertain

Microfossils of the Gunflint Chert
  • Gunflint fossil organisms resemble photosynthetic
  • The rock containing these organisms contains
    organic compounds that are regarded as the
    breakdown products of chlorophyll.
  • The Gunflint Chert organisms altered the
    composition of the atmosphere by producing

The Rise of Eukaryotes
  • The appearance of eukaryotes is a major event in
    the history of life.
  • Eukaryotes have the potential for sexual
    reproduction, which increases variation through
    genetic recombination.

The Rise of Eukaryotes
  • Genetic recombination provides greater
    possibilities for evolutionary change.
  • Diversification of life probably did not occur
    until after the advent of sexual reproduction, or
    until oxygen levels reached a critical threshold.

Eukaryotic cells can be differentiated from
prokaryotic cells on the basis of size.
  • Eukaryotes tend to be much larger than
    prokaryotes (larger than 60 microns, as compared
    with less than 20 microns).

The Rise of Eukaryotes
  • Eukaryotes appeared by Archean time (as
    determined by molecular fossils or biochemical
  • Larger cells begin to appear in the fossil record
    by 2.7 b.y. to 2.2 b.y.
  • Eukaryotes began to diversity about 1.2 to 1.0
    b.y. ago.

  • Eukaryotes
  • Single-celled, spherical microfossils
  • Thick organic covering
  • May have been phytoplankton
  • First appeared 1.6 b.y. ago (at
    Paleoproterozoic-Mesoproterozoic boundary)
  • Some resemble cysts or resting stages of modern
    marine algae called dinoflagellates.

  1. Reached maximum diversity and abundance 850 m.y.
  2. Declined during Neoproterozoic glaciation
  3. Few acritarchs remained by 675 m.y. ago
  4. Extinct in Ordovician time
  5. Useful for correlating Proterozoic strata

The First Metazoans (Multicellular Animals)
  • Metazoans are multicellular animals with various
    types of cells organized into tissues and organs.
  • Metazoans first appeared in the Neoproterozoic,
    about 630 m.y. ago (0.63 b.y.). Preserved as
    impressions of soft-bodied organisms in

Examples of metazoan fossils in the Proterozoic
  • Ediacara fauna - Imprints of soft-bodied
    organisms, first found in Australia in the 1940's
  • Metazoan eggs and embryos in uppermost
    Neoproterozoic Doushantuo Formation, South China
  • Trace fossils of burrowing metazoans in rocks
    younger than the Varangian glaciation.
  • Tiny shell-bearing fossils (small shelly fauna)

  • Geologic time scale across the
    Precambrian-Cambrian boundary, showing the
    Ediacaran fauna and other faunas.

Ediacara fauna
  • Ediacara fauna is an important record of the
    first evolutionary radiation of multicellular
  • Some were probably ancestral to Paleozoic
  • Oldest Ediacara-type fossils are from
    China.Youngest Edicara-type fossils are Cambrian
    (510 m.y., Ireland).

Types of Ediacara fossils
  • Discoidal
  • Frondlike
  • Elongate or ovate

Ediacara fauna
  • Because the Ediacara creatures are not really
    similar to animals that are living today, this
    has led to the suggestion that they be placed in
    a separate taxonomic category or new phylum.
  • The name proposed for this new category is
    Vendoza (named after the Vendian, or the latest
    part of the Neoproterozoic in Russia).

Small Shelly Fauna The Origin of Hard Parts
  • Small fossils with hard parts or shells appeared
    in the Neoproterozoic.

Small Shelly Fauna The Origin of Hard Parts
  • Cloudina, an organism with a small, tubular
    shell of calcium carbonate (CaCO3).
  • Resembles structures built by a tube-dwelling
    annelid worm.
  • Earliest known organism with a CaCO3 shell.
  • Found in Namibia, Africa.

Small Shelly Fauna The Origin of Hard Parts
  • Other latest Proterozoic and earliest Cambrian
    small fossils with shells include
  • Possible primitive molluscs
  • Sponge spicules,
  • Tubular or cap-shaped shells, and
  • Tiny tusk-shaped fossils called hyoliths
  • Some early shelly material is made of calcium

Precambrian Trace Fossils
  • Trails, burrows, and other trace fossils are
    found in late Neoproterozoic rocks.
  • In rocks deposited after the Neoproterozoic
    Varangian glaciation.
  • Mostly simple, shallow burrows.
  • Trace fossils increase in diversity, complexity,
    and number in younger (Cambrian) rocks.

What stimulated the appearance of metazoans?
  • May be related to the accumulation of sufficient
    oxygen in the atmosphere to support an
    oxygen-based metabolism.
  • Ancestral metazoans may have lived in "oxygen
    oases" of marine plants.
  • Ediacaran life may have evolved gradually from
    earlier forms that did not leave a fossil record.

  • Review of Proterozoic Events

  • Review
  • of the
  • Precambrian
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