Early Paleozoic (midterm 2) Flashcards
(27 cards)
What are the 3 earliest periods in the Early Paleozoic Era - Phanerozoic Eon?
Cambrian
Ordovician
Silurian
Explain the relative changes in sea level during the early Paleozoic
Sea level started off lower than our modern sea level because of lots of glaciers
Then by the Ordovician the sea level is above our modern level for the rest of the early Paleozoic
By the Paleozoic, ____ major continents were present
6
By the early Paleozoic, what two major parts did each of the 6 major continents have? (+ what is an Epeiric sea?)
- A relatively stable craton over which epeiric seas transfressed and regressed
> Epeiric sea = a broad shallow sea that covers part of a continent - Elongate mobile belts in which mountain building took place
What is a mobile belt? In north america what were the four major mobile belts during this time?
Mobile belt = elongate areas of mountain-building activity
> convergent plate boundaries
4 North American belts at the time: Franklin, Cordilleran, Ouachita, and Appalachian
The Paleozoic is less well known than the ________ and _________. Why?
Mesozoic and Cenozoic (2nd two eras of the Phanerozoic Eon)
- bc magnetic anomaly patterns in the Paleozoic ocean crust were largely destroyed during the formation of Pangaea
- also we use fossils to determine paleogeography but the further back you go the more difficult this is to do because old rocks are subducted and deformed
What were the 6 main continents at the time?
- Baltica
- China
- Gondwana
- Kazakhstania
- Laurentia
- Siberia
Describe the Late Cambrian Paleogeography
- polar regions mostly ice free
- Epeiric seas (light blue) covered parts of continents
- Eastern Laurentia was a passsive continental margin
Describe the Late Ordovician Paleogeography
- Gondwana moved south across the pole
- evidence of glaciations by tillite in North America
- Avalonia separated from Gondwana, moved northeastward, collided with Baltica
- East margin of Laurentia became active convergent boundary
Describe the Middle Silurian Paleogeography
- Balitca-Avalonia collided with Laurentia, closing northern lapetus Ocean
- Southern lapetus Ocean remained open
What is a Cratonic Sequence? What two processes can it show
It is a lithostratigraphic unit representing sea level changes
> they are bound by unconformities - time gaps in the rock record representing periods of erosion or non-deposition
Transgression: sea level rise
Regression: sea level fall
Explain the process of Transgression
Transgression:
- further offshore (deeper into the water) = less energy - finer settlements settling (limestone mud)
> shale deposits between offshore and near shore
- nearshore (where water meets land) = higher energy - produces sandstone type rocks (coarse grained)
- sea level rising - sandstone facies deposited overtop of land surface
- shale facies deposited overtop of sandstone
- limestone deposited overtop of shale
*sequence > bottom up: land, sandstone, shale, limestone
What does facies mean
“Facies” means all the characteristics/aspects of the rocks - chemistry, mineralogy, physical attributes, any biology/fossils in there?
Explain the process of Regression
- sea level falling
- opposite depositional sequence to transgression
- shale deposited over limestone, sandstone deposited over shale
(bottom up: land, limestone, shale, sandstone)
What kind of cratonic sequence is the Grand Canyon? What time period does this sequence come from?
It is a transgressive sequence (sea level rise)
They are Cambrian rocks (came from the Cambrian period)
On the cratonic sequences diagram, what does the blue, white, and brown areas mean?
blue = mountain building
white = rock sequences
brown = unconformity
What was the Sauk Sequence? When was it?
Neoproterozoic - Early Ordovician
- first major transgression onto the North American continent (transgression of the sauk sea)
- deposition of marine sediments on Appalachian and Cordilleran borders of the craton
- tropical climate caused erosion of craton
What was the Tippecanoe Sequence? When was it?
Ordovician-Silurian
Sauk Sea regressed during the Early Ordovician > high erosion > unconformity between the Sauk and Tippecanoe sequences
Transgression began again in Middle Ordovician > deposition of sandstone, widespread carbonates > great fossils
(Regression again during the Late Silurian)
What is the world’s largest trilobite and where was it found?
Isotelus rex
- Ordovician
- found in tyndall stone near churchill, Manitoba
What are reefs? What were the first reef builders and what are they today?
They are limestone structures made by living organisms
- first builders of reef-like structures were archaeocyathids (they are often very well preserved because they can preserve themselves kinda and there’s lots of burial
- today’s major reef-buliders are corals
What are barrier reefs?
Long narrow structures that form parallel to the shoreline
What are the calcium-carbonate secreting organisms in the reef that deposit limestone?
Corals, brachiopods, stromatoporoids, bryozoans
Describe the development of reefs during the Silurian in North America - how did this make evaporites?
- development of reefs in warm, shallow marine environments
- barrier reefs can cut off water from the open seas > results in evaporation of seawater, deposition of evaporites and evaporite minerals
When did reefs develop?
Silurian period
