UNIVERSITY OF SOUTH ALABAMA
Last time we covered…
1) Hydrothermal vents (Jaime)
2) Caribbean Plate tectonics (Zeb)
MAS 603: Geological Oceanography
Lecture 6: Proterozoic Geology
Today’s Agenda
The Proterozoic Eon
Proterozoic Geology
1) The Proterozoic time frame
2) Paleogeography
3) Tectonics
4) Paleoclimatology
Eon
The Proterozoic Eon
Eon
Time
Time
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.1 GA to 2.5 GA
Hadean
4.6 GA to 4.1 GA
The Proterozoic Eon
Eon
Time
Phanerozoic
550 MA to 0 MA
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.1 GA to 2.5 GA
Archean
4.1 GA to 2.5 GA
Hadean
4.6 GA to 4.1 GA
Hadean
4.6 GA to 4.1 GA
Division
Age
Neoproterozoic
900 MA to 550 MA
Mesoproterozoic
1.6 GA to 900 MA
Paleoproterozoic
2.5 GA to 1.6 GA
• Paleo- old
• Meso-middle
• Neo-new
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The Canadian Shield
Proterozoic Paleogeograpy
Neoproterozoic 650 MA
• Shield: very old
(>2.5 GA)
igneous and
metamorphic
“basement” rocks
(Granulites)
• Platform: younger
(550 MA-2.5 GA)
sedimentary rocks
• This is about as far back as we can go with detailed paleogeography
http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
Proterozoic Paleogeograpy
Proterozoic Paleogeograpy
• As far as we can tell, there was no modern plate tectonics prior
to the early Proterozoic.
Rodinia
(the first supercontinent)
The Earth
1.0 GA
• But we can “guestimate” back to about 1 GA
Modern Plate Tectonics
• Rigid lithospheric plates “float” atop ductile asthenosphere
Proterozoic Tectonics
• The first evidence of
divergent and
convergent plate
tectonics was during
the Paleoproterozoic
(2.1 GA) in the
Slave Province of
the Canadian Shield
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Proterozoic Tectonics
• The first evidence of
divergent and
convergent plate
tectonics was during
the Paleoproterozoic
(2.1 GA) in the
Slave Province of
the Canadian Shield
Proterozoic Tectonics
Proterozoic Tectonics
• Coronation Geosyncline
Proterozoic Tectonics
• A paleogeographic
reconstruction of the
Coronation
Geosyncline at 2.1 GA
would look like this:
• Ternary rifting patterns
have also been
recognized.
• They were mostly filled
with coarse gravel and
breccia (phase 1 fill in
the Coronation
Geosyncline)
Triple Junction
Proterozoic Tectonics
• But the Coronation
Geosyncline ocean did
not last a long time.
Proterozoic Tectonics
• But the Coronation
Geosyncline ocean did
not last a long time.
• Granite was emplaced
along the western side
around 1.8 GA
indicating a plate
collision.
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Proterozoic Tectonics
Proterozoic Tectonics
• But the Coronation
Geosyncline ocean did
not last a long time.
• But the Coronation
Geosyncline ocean did
not last a long time.
• Granite was emplaced
along the western side
around 1.8 GA
indicating a plate
collision with another
continent.
• Granite was emplaced
along the western side
around 1.8 GA
indicating a plate
collision with another
continent.
Proterozoic Tectonics
The collision is known as the
Wopmay Orogeny
Other Proterozoic Orogenies
Starting in the Paleoproterzoic, orogenies became very common
around the world.
• The culprit that hit us was Australia seen here fleeing the scene
of the accident about 500 MA after the incident
Grenville
Orogeny
Proterozoic Climate
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Proterozoic Climate
Neoproterozoic 650 MA
Proterozoic Climate
Neoproterozoic 650 MA
There is something similar about the Neoproterozoic and Modern Earth…
Modern Climate
There is something similar about the Neoproterozoic and Modern Earth…
Ice caps at the poles
Modern Climate
Key Points:
(1) Ice comes in several “flavors” (types of glaciers)
(2) Polar ice isn’t always present on the Earth’s surface.
Today 0 MA
There is something similar about the Neoproterozoic and Modern Earth…
Ice caps at the poles
Modern Climate
Continental Glaciers
•Continental glaciers alternate in
extent (view to right from 18 KA)
and they are important. They are
responsible for dramatic sea level
changes (transgressions and
regressions +/- 300 feet)
• Alpine (valley) glaciers
• Continental glaciers (Ice Caps)
Proterozoic Glaciations
We have pretty good evidence that glaciations occurred several
times during the geological record.
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Proterozoic Glaciations
Proterozoic Glaciations
We have pretty good evidence that glaciations occurred several
times during the geological record.
We have pretty good evidence that glaciations occurred several
times during the geological record.
•Fossils (some are temperature-dependent, but not all)
•Paleomagnetism (low latitude=tropical; high latitude = polar)
•Lithology (unique glacial deposits)
•Fossils (some are temperature-dependent, but not all)
•Paleomagnetism (low latitude=tropical; high latitude = polar)
•Lithology (unique glacial deposits)
Tillite
Till
Proterozoic Glaciations
We find tillites many times in the rock record in many places
around the world. Including several glaciations during the
Proterozoic:
1) 2.4-2.2 GA (Canada only?) Huronian Glaciation
Proterozoic Glaciations
We find tillites many times in the rock record in many places
around the world. Including several glaciations during the
Proterozoic:
1) 2.4-2.2 GA (Canada only?) Huronian Glaciation
2) 750-600 MA (world-wide?) Varangian/Sturtian Glaciation
Dropstone
Proterozoic Glaciations
till
Proterozoic Glaciations
The Varangian glaciation was
weird; many of the best
glaciated sites were near the
paleoequator.
http://www.snowballearth.org/end.html
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Proterozoic Glaciations
Snowball Earth
The Varangian glaciation was
weird; many of the best
glaciated sites were near the
paleoequator.
•Geological evidence suggests
2 or 3 distinct Snowball Earth
periods.
Several explanations have been
proposed
1) steeper orbital inclination
2) faster spreading rates
3) bad data
4) the Earth literally froze over
Snowball Earth
•Estimated temperatures at
the equator during the height
of the Snowball Earth were
-50 ºC
http://zebu.uoregon.edu/2002/ph123/snowball.gif
Snowball Earth
Weirder still, glacial deposits are commonly directly overlain by
strange limestones (cap carbonates) that were deposited very
quickly in “tropical” conditions.
•This is cold… much colder
than anything we’ve ever
experienced and some would
say, much too cold to be
possible because of Albedo
effects.
http://zebu.uoregon.edu/2002/ph123/snowball.gif
Snowball Earth
Neoproterozoic outcrop (750 million years old) in Northern Namibia.
The cloud is dust blown in from the coastal desert of Namibia (we are
looking west).
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Another view of the outcrop in Namibia. The dry river valley is full
of baboons, elephants and increasingly, geologists.
Arguably the most important snowball earth outcrop on the planet. The
next image is Hoffman’s geological interpretation.
Hoffman
ate
bon
Car
Cap
e
ictit
diam
te
ona
arb
lf C
She
This is Paul Hoffman’s favorite outcrop. Here you can see the contact
between glacial deposits and cap carbonate.
A close up of the cap carbonate above the
glacial diamictite. This rock consists of
bladed calcite, but might have originally
been aragonite. Isotopic data suggests very
rapid sedimentation from very warm sea
water.
A huge bluff of cap carbonate (so called because these limestones
“cap” the sedimentary sequence.
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Proterozoic Fossils
Next Time
1. Monday: Snowball Earth Discussion (Lucie)
2. Wed: BIFS
Severe
environmental
changes drives
evolutionary
adaptation.
http://www.snowballearth.org/end.html
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