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Home , Huronian glaciation

UNIVERSITY OF SOUTH ALABAMA Last time we covered…

1) Hydrothermal vents (Jaime) MAS 603: Geological Oceanography 2) Caribbean Plate tectonics (Zeb)

Lecture 6: Geology

Today’s Agenda The Proterozoic Eon

Proterozoic Geology

1) The Proterozoic time frame 2) Paleogeography Eon Time 3) Tectonics 550 MA to 0 MA 4) Proterozoic 2.5 GA to 550 MA 4.1 GA to 2.5 GA 4.6 GA to 4.1 GA

The Proterozoic Eon The Proterozoic Eon

Eon Time Eon Time Division Age Phanerozoic 550 MA to 0 MA Phanerozoic 550 MA to 0 MA 900 MA to 550 MA Proterozoic 2.5 GA to 550 MA Proterozoic 2.5 GA to 550 MA 1.6 GA to 900 MA Archean 4.1 GA to 2.5 GA Archean 4.1 GA to 2.5 GA 2.5 GA to 1.6 GA Hadean 4.6 GA to 4.1 GA Hadean 4.6 GA to 4.1 GA • Paleo- old • Meso-middle • Neo-new

1 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

http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif • This is about as far back as we can go with detailed paleogeography

Proterozoic Paleogeograpy Proterozoic Paleogeograpy

• As far as we can tell, there was no modern plate tectonics prior to the early Proterozoic. (the first supercontinent)

The 1.0 GA

• But we can “guestimate” back to about 1 GA

Modern Plate Tectonics Proterozoic Tectonics

• Rigid lithospheric plates “float” atop ductile asthenosphere • The first evidence of divergent and convergent plate tectonics was during the Paleoproterozoic (2.1 GA) in the Slave Province of the Canadian Shield

2 Proterozoic Tectonics 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 • Coronation Geosyncline

Proterozoic Tectonics Proterozoic Tectonics

• A paleogeographic • Ternary rifting patterns reconstruction of the have also been Coronation recognized. Geosyncline at 2.1 GA • They were mostly filled would look like this: with coarse gravel and breccia (phase 1 fill in the Coronation Geosyncline)

Triple Junction

Proterozoic Tectonics Proterozoic Tectonics

• But the Coronation • But the Coronation Geosyncline ocean did Geosyncline ocean did not last a long time. not last a long time.

• Granite was emplaced along the western side around 1.8 GA indicating a plate collision.

3 Proterozoic Tectonics Proterozoic Tectonics

• But the Coronation • But the Coronation Geosyncline ocean did Geosyncline ocean did not last a long time. not last a long time.

• Granite was emplaced • Granite was emplaced along the western side along the western side around 1.8 GA around 1.8 GA indicating a plate indicating a plate collision with another collision with another continent. The collision is known as the continent. Wopmay Orogeny

Proterozoic Tectonics 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

4 Proterozoic Climate Proterozoic Climate

Neoproterozoic 650 MA Neoproterozoic 650 MA

There is something similar about the Neoproterozoic and Modern Earth… There is something similar about the Neoproterozoic and Modern Earth… Ice caps at the poles

Modern Climate Modern Climate

Today 0 MA Key Points: (1) Ice comes in several “flavors” (types of glaciers) (2) Polar ice isn’t always present on the Earth’s surface.

There is something similar about the Neoproterozoic and Modern Earth… • Continental glaciers (Ice Caps) Ice caps at the poles • Alpine (valley) glaciers

Modern Climate Proterozoic Glaciations

Continental Glaciers We have pretty good evidence that glaciations occurred several times during the geological record. •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)

5 Proterozoic Glaciations Proterozoic Glaciations

We have pretty good evidence that glaciations occurred several We have pretty good evidence that glaciations occurred several times during the geological record. times during the geological record.

•Fossils (some are temperature-dependent, but not all) •Fossils (some are temperature-dependent, but not all) •Paleomagnetism (low latitude=tropical; high latitude = polar) •Paleomagnetism (low latitude=tropical; high latitude = polar) •Lithology (unique glacial deposits) •Lithology (unique glacial deposits) Tillite Till

Proterozoic Glaciations Proterozoic Glaciations

We find tillites many times in the rock record in many places We find tillites many times in the rock record in many places around the world. Including several glaciations during the around the world. Including several glaciations during the Proterozoic: Proterozoic: 1) 2.4-2.2 GA (Canada only?) Huronian Glaciation 1) 2.4-2.2 GA (Canada only?) Huronian Glaciation 2) 750-600 MA (world-wide?) Varangian/

Dropstone till

Proterozoic Glaciations Proterozoic Glaciations

The Varangian glaciation was weird; many of the best glaciated sites were near the paleoequator.

http://www.snowballearth.org/end.html

6 Proterozoic Glaciations

The Varangian glaciation was •Geological evidence suggests weird; many of the best 2 or 3 distinct Snowball Earth glaciated sites were near the periods. paleoequator.

Several explanations have been proposed

1) steeper orbital inclination 2) faster spreading rates 3) bad data 4) the Earth literally froze over http://zebu.uoregon.edu/2002/ph123/snowball.gif

Snowball Earth Snowball Earth

•Estimated temperatures at Weirder still, glacial deposits are commonly directly overlain by the equator during the height strange limestones (cap carbonates) that were deposited very of the Snowball Earth were quickly in “tropical” conditions. -50 ºC

•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).

7 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.

e Hoffman nat rbo Ca Cap

tite mic 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.

8 Proterozoic Fossils Next Time

1. Monday: Snowball Earth Discussion (Lucie) Severe environmental 2. Wed: BIFS changes drives evolutionary adaptation.

http://www.snowballearth.org/end.html

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