UNIVERSITY OF SOUTH ALABAMA
GY 112: Earth History
Lecture 20: Proterozoic Part 3
Paleoclimate
Instructor: Dr. Douglas W. Haywick
Last Time
Proterozoic Tectonics 2
1) Wilson Cycle
2) The Trans-Hudson Orogenic Belt
3) The Grenville Orogeny
• This is now called the
Wilson Cycle in honor of
J. Tuzo Wilson who first
suggested it for the
Atlantic Ocean
Other Proterozoic Orogenies
And starting in the Paleoproterzoic, orogenies became very
common around the world.
Grenville
Orogeny
Today’s Agenda
The Proterozoic Part 3
1)
2)
3)
Glaciations: what happens and why
Glaciations in the Proterozoic
Snowball Earth Hypothesis (neato cool!)
(web notes 20)
Proterozoic Climate
Neoproterozoic 650 MA
There is something similar about the Neoproterozoic and Modern Earth…
Proterozoic Climate
Neoproterozoic 650 MA
There is something similar about the Neoproterozoic and Modern Earth…
Ice caps at the poles
Modern Climate
Today 0 MA
There is something similar about the Neoproterozoic and Modern Earth…
Ice caps at the poles
Modern Climate
Key Points:
Modern Climate
Key Points:
(1) Ice comes in several “flavors” (types of glaciers)
Modern Climate
Key Points:
(1) Ice comes in several “flavors” (types of glaciers)
(2) Widespread ice (e.g., Antarctic) isn’t always present on the
Earth’s surface.
Modern Climate
Types of glaciers
Modern Climate
Types of glaciers
• Alpine (valley) glaciers
http://www.scienceclarified.com/images/uesc_05_img0282.jpg
Modern Climate
Types of glaciers
• Continental glaciers (Ice Sheets)
http://www.scienceclarified.com/images/uesc_05_img0282.jpg
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!)
Modern Climate
Sometimes continental glaciers were extensive…
Land bridge
Land bridge
Modern Climate
Sometimes continental glaciers were entirely absent…
Seaway
Paleoclimate Phases
We now recognize two major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
65 MA
http://www.oceansofkansas.com/images2/wis-map3.jpg
Paleoclimate Phases
We now recognize two major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
2) Icehouse Earth
(continental glaciers present)
Paleoclimate Phases
We now recognize two major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
2) Icehouse Earth
(continental glaciers present)
a) Glacial stage (18 KA)
http://www.snowballearth.org/end.html
Paleoclimate Phases
We now recognize two major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
2) Icehouse Earth
(continental glaciers present)
a) Glacial stage (18 KA)
b) Interglacial stage (Today)
http://www.snowballearth.org/end.html
Paleoclimate Phases
We now recognize two major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
2) Icehouse Earth
(continental glaciers present)
a) Glacial stage (18 KA)
b) Interglacial stage (Today)
http://www.snowballearth.org/end.html
To be Continued
(in the Cenozoic)
Proterozoic Glaciations
You should be asking yourself, how can geologists tell that
glaciations occurred in the rock record?
Proterozoic Glaciations
You should be asking yourself, how can geologists tell that
glaciations occurred in the rock record?
•Fossils (some are temperature-dependent, but not all)
Proterozoic Glaciations
You should be asking yourself, how can geologists tell that
glaciations occurred in the rock record?
•Fossils (some are temperature-dependent, but not all)
•Paleomagnetism (low latitude=tropical; high latitude = polar)
Proterozoic Glaciations
You should be asking yourself, how can geologists tell that
glaciations occurred in the rock record?
•Fossils (some are temperature-dependent, but not all)
•Paleomagnetism (low latitude=tropical; high latitude = polar)
•Lithology (unique glacial deposits)
Proterozoic Glaciations
You should be asking yourself, how can geologists tell that
glaciations occurred in the rock record?
•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.
Proterozoic Glaciations
Including several glaciations during the Proterozoic:
Dropstone
till
Proterozoic Glaciations
Including several glaciations during the Proterozoic:
1) 2.4-2.2 GA (Canada only?) Huronian Glaciation
Dropstone
till
Proterozoic Glaciations
Including several glaciations during the Proterozoic:
1) 2.4-2.2 GA (Canada only?) Huronian Glaciation
2) 750-600 MA (world-wide) Varangian Glaciation
(Now classified as 2 separate glaciations: Sturtian (730-700MA and Marinoan: 660-635 MA)
http://www.snowballearth.org/end.html
Proterozoic Glaciations
The Varangian glaciation was
weird; many of the best
glaciated sites were near the
equator!
Proterozoic Glaciations
The Varangian glaciation was
weird; many of the best
glaciated sites were near the
equator!
This lead several people to
conclude that the Earth
literally froze over… 2 or 3
times
Snowball Earth
The Varangian glaciation was
weird; many of the best
glaciated sites were near the
equator!
This lead several people to
conclude that the Earth
literally froze over… 2 or 3
times
It was a Snowball Earth
http://zebu.uoregon.edu/2002/ph123/snowball.gif
Snowball Earth
•Estimated temperatures at
the equator during the height
of the Snowball Earth were
-50 ºC
•This is cold… much colder
than anything we’ve ever
experienced and some would
say, much too cold to be
possible.
http://zebu.uoregon.edu/2002/ph123/snowball.gif
Snowball Earth
But that isn’t the end of the weirdness…
Glacial deposits are commonly directly overlain by strange
limestones that were deposited very quickly in tropical conditions.
Snowball Earth
Stable isotope geochemistry
implies a dramatic change in
temperature…
…from -50ºC to +50ºC (-60ºF
to 122 ºF)
Snowball Earth
Stable isotope geochemistry
implies a dramatic change in
temperature…
…from -50ºC to +50ºC (-60ºF
to 122 ºF)
Stable isotopes (C12/C13)also
suggest a possible explanation
for the end of the Snowball
cycle(s)
Snowball Earth
Snowball Earth
The Mechanism:
CO2 production from
volcanoes
Today’s Homework
1. Study! (Lecture test 2 two weeks from today)
2. Study! (Lab test 2- Haywick’s labs tomorrow!)
Next Time
Lecture: Proterozoic Fossils
GY 112: Earth History
Lecture 20: Proterozoic Paleoclimate
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.