Precambrian (Proterozoic) Flashcards
When does the Proterozoic eon occur?
Between the start of an oxygenated atmosphere and the FIRST animals
How do these iron banded formation (BIFs) form?
When iron in the ocean reacts with oxygen (made form the cyanobacteria) and rusts
What do Proterozoic rocks consist of?
Banded iron (rusted iron) marking a new oxygen-rich atmosphere
What happens with banded iron formations with oxygen?
These BIFs continue to form as long as iron is available to oxidize with, when there is no more iron to oxidize, the oxygen has no where to go except in the atmosphere which builds up over time
What does the Proterozoic mark?
What do we call these events?
The beginning of MODERN MOUNTAIN BUILDING EVENTS
Are called an OROGENY
What does an orogeny form?
A mountain belt called an orogen
What is the difference between Archean plate tectonics compared to Modern plate tectonics?
Archean plates were solid but they were still very hot and easily deformed (not rigid)
These tectonics resulted in continents squishing together rather than crumpling
Modern tectonics are rigid, brittle, and cold
What are the three stresses that operate on EARTH?
Tension (moving apart/divergent) , Compression (coming together/convergent) , and Shear (sliding past/transform)
Foot wall and Hang wall
Foot wall = the block you stand on
Hanging wall = the block you hang your lantern on
How do NORMAL faults form?
Due to tension (pulling apart)
Hanging wall goes DOWN
Footwall goes UP
How do REVERSE faults form?
Due to compression (squeezing)
Hanging wall goes UP
Footwall goes DOWN
Where on Earth preserves one of the earliest orogenic events recorded on Earth?
What is this place called and what does it contain?
The SLAVE PROVINCE of CANADA
WOPMAY OROGEN
Intrusive igneous rocks, metamorphic rocks, and faults
What does the Wopmay Orogen represent? What was it made from?
The attachment of a volcanic island onto the side of NA
This volcanic island chain added new land, as it gets accreted the volcanic island forms intrusive igneous rocks, metamorphic rocks, and reverse faults (compression)
What happened to cause the creation the first craton during the Proterozoic eon?
The 6 Archean-age terranes became fused in a massive collision, this continental collision began 1.9 Billion years ago
What happened during the collision of these 6 terranes?
The collision pushed up the Trans-Hudson Orogen
THIS OROGEN MARKS THE COLLISION OF THE TERRANES
What is unique about Mt. Rushmore in regards to its composition?
What Oregon is it apart of? Where??
Mt. Rushmore in the Black Hills of South Dakota is part of the Trans-Hudson Orogen
Mt. Rushmore is 1.7 billion year old granite but is SURROUNDED by 1.9-1.8 Billion year old metamorphic rocks
What was before Pangea?
When was it assembled?
A PROTEROZOIC-AGE SUPERCONTINENT called RODINIA
About 1.1 billion years ago
What was the assembling of Rodinia associated with?
The accretion of numerous terranes as landmasses were added to the NORTH AMERICAN CRATON
When did the assembling of Rodinia take place?
1.8-1 Billion years ago during the Proterozoic
When did Rodinia split?
800 Million years ago, in doing so, liberated NA until the time of PANGEA
North America and Greenland leave as Laurentia
What happens following the split of Rodinia?
The later events of the Proterozoic are preserved in DEATH VALLEY
DEATH VALLEY PICKS UP WHERE RODINIA LEFT OFF
What are the events leading to the first coastline and the creation of Death Valley?
- California coast was first exposed when NA was rifted away from Antarctica, California has touched the ocean ever since
- The western edge of the craton marks the torn edge of the continent when Rodinia split, torn edge faces the ocean
- This rifting event created California’s first coastline and Death valley was right on top of it, coast was at margin of the craton
Where is Death Valley’s rock record located?
Atop the craton where it was created
How many ice ages has there been and when did the most severe begin?
Have been several ice ages throughout the known history of Earth
Most severe began about 720 million years ago
What is Snowball Earth? When did it occur?
Glaciers were present on every continent
About 720-635 million years ago
What evidence does Death Valley show that proves the Snowball Earth?
Where in Death Valley?
The Kingston Peak Formation in Death Valley consists of mudstone with large boulders in it
(traces of glaciers)
What are dropstones?
Large boulders that have been picked up by glaciers as they move, broken off in icebergs, and dropped on the seafloor consisting of deep sea mud
Why did the Snowball Earth occur?
Because nearly all the landmasses were located at the south pole, polar continents tend to accumulate glaciers
What had returned due to Snow Ball Earth?
Banded Iron Formations (BIFs) return due to the sealing of the ocean
An ocean sealed with ice loses its oxygen quickly and available iron can build up below
What prevents oxygen from entering the ocean?
The sea surface becomes sealed with ice sheets, these ice sheets prevent oxygen from entering
Makes Iron build up extensively in the ocean
How does BIFs form in regards to the presence of ice sheets?
BIFs form when the ice sheets melts, reintroducing oxygen back into the ocean
These cycles probably occurred multiple times
