7 Precambrian History Flashcards
Define stratigraphic subdivision
A stage is a crucial subdivision of strata, each minutely following each other while bearing a unique, distinctive assemblage of fossils. Thus, stages can be described as a group of strata consisting of the same major fossil assemblages.
What happens when the sea level fall (shoreline regression)
Tectonic Uplift
What happens when sea levels rise (shoreline transgression)
Tectonic collapse
Define stratigraphic sequences
Packages of rocks bounded by unconformities
What are the two ways stratigraphic subdivisions can be separated?
- Sequences by time
- Sequences by depth
Where is another name for the Laurentia?
North American Craton
What time frame was the crystalline basement?
Archean to Paleoproterozoic (1.8-2.8 Ba)
How many parts are there to the crystalline basement?
Many different parts and is complex
Where is Canada is the crystalline basement exposed?
The Canadian Shield
What’s the main difference between a failed and successful rift?
A successful rift differs from a failed rift in that the asthenosphere makes it all the way to the surface and is able to form new crust
Define a rift
A rift is one or more depressions (GRABENS) resulting from tectonic extension that caused faulting, stretching and thinning of the asthenosphere
What’s an example of a failed (abortive) rift?
Sea between the UK and Europe
What time frame was the Wernecke Supergroup?
Paleoproterozoic to Mesoproterozoic (1.8- ~1.3 Ba)
What belt is the Wernecke supergroup in and what is special about it?
Has the oldest rocks and is in the foreland belt
What fossils do we see in Wernecke Group and what do these fossils look like?
Stromatolites can be small or large and are the result of microbial life
What conditions need to exist for stromatolites to form?
There has to be very contact with other organisms hence why they grew so large when it was only microbial life
What is an important fossil fact about stromatolites?
They are the oldest formation to exist
What time frame was the Purcell/ Belt Supergroup?
Mesoproterozoic
What kind of rock is in the Purcell/ Belt Supergroup?
Platform/ shelf basin carbonates
Where does most of the Purcell/ Belt Supergroup exist? (2)
- Glacier National Park, Montana
- Waterton Lakes National Park, SW AB
Why does the Purcell-Belt Supergroup have two names?
Because its in both Canada and the US that named them differently (Purcell-Canada, and Belt-USA)
What conditions were the Purcell-Belt Supergroup formed?
Deposited in deltaic to deep marine enviorments
What time frame was the Mackenzie Mountains Supergroup formed?
Mesoproterozoic to Neoproterozoic (~1.3-0.8 Ba)
What kind of fossils would you see in the Mackenzie Mountains Supergroup?
Stromatolite reefs
