UNIVERSITY OF SOUTH ALABAMA

GY 112: Earth History

Lecture 20: Proterozoic Part 2 Paleoclimate

Instructor: Dr. Douglas W. Haywick Last Time

Proterozoic Part 1: Tectonics 1) The Proterozoic time frame 2) Paleogeography 3) Tectonics (Wopmay Orogeny) 4) The Wilson cycle 5) The Trans-Hudson Orogenic Belt 6) The Grenville Orogeny

(Web Lectures 18 and 19) The Proterozoic Eon

Eon Time Division (ERA) Age Phanerozoic 550 MA to 0 MA Neoproterozoic 900 MA to 550 MA Proterozoic 2.5 GA to 550 MA Mesoproterozoic 1.6 GA to 900 MA Archean 4.1 GA to 2.5 GA Paleoproterozoic 2.5 GA to 1.6 GA Hadean 4.6 GA to 4.1 GA • Paleo- old • Meso-middle • Neo-new Proterozoic Paleogeography

Rodinia (the first supercontinent)

The Earth 1.0 GA

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

• Coronation Geosyncline • Wopmay Orogen • Bathurst Aulocogen • Athapuscow Aulocogen

Proterozoic Tectonics

• A paleogeographic reconstruction of the Coronation Geosyncline 2.1 GA would look like this:

Proterozoic Tectonics

• Linear trenches also opened up.

• They were mostly filled with coarse gravel and breccia (phase 1 fill in the Coronation Geosyncline)

• Ternary rifting patterns Triple Junction

Chalk board Proterozoic Tectonics

• In any triple junction, one of the “arms” will become a failed rift or an Aulcogen. Two will continue to spread into an ocean Proterozoic Tectonics

• This mountain-building event is called the Wopmay Orogeny

Proterozoic Tectonics

So what hit us?

• The culprit was Australia seen here fleeing the scene of the accident about 500 MA after the incident • This is now called the Wilson Cycle in honor of J. Tuzo Wilson who first suggested it for the Atlantic Ocean Other Proterozoic Orogenies

Starting in the Paleoproterzoic, orogenies became very common around the world. Grenville Orogeny Today’s Agenda

The Proterozoic Part 2

1) Glaciations: what happens and why 2) Glaciations in the Proterozoic 3) 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)

To be Continued http://www.snowballearth.org/end.html (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) Till Tillite 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! (Thursday after Spring Break) 2. Study! (Lab test 2- Haywick’s labs tomorrow!)

Next Time

Quiz: Compare and contrast Lecture: Proterozoic Fossils GY 112: Earth History

Lecture 20: Proterozoic Paleoclimate

Instructor: Dr. Doug Haywick [email protected]

This is a free open access lecture, but not for commercial purposes. For personal use only.