Early Paleozoic (midterm 2) Flashcards
What are the 3 earliest periods in the Early Paleozoic Era - Phanerozoic Eon?
Cambrian: 542 - 488 Ma
Ordovician: 488 - 444 Ma
Silurian: 444 - 416 Ma
Explain the relative changes in sea level during the early
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
When did the supercontinent Pannotia begin to break up?
550 mya
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
> compressional forces from convergent plate boundaries
4 North American belts at the time: Franklin, Cordilleran, Ouachita, and Appalachian
To reconstruct paleogeography, what kind of data do geologists analyze?
- paleoclimates, paleomagnetics, fossils, stratigraphy, sedimentology, and tectonics
The Paleozoic is less well known than the ________ and _________. Why?
The Paleozoic is significantly better known than the _________
Mesozoic and Cenozoic (2nd two eras of the Phanerozoic Eon)
- bc magnetic anomaly patterns in the Paleozoic ocean crust were largely destroyed by subduction 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
Proterozoic
What were the 6 main continents at the time (and which modern areas they included)
- Baltica (Russia, most of northern Europe)
- China (3 small continents that were very close together; China, Indochina, Malay Peninsula
- Gondwana (Africa, Antarctica, Australia, Florida, India, and parts of the Middle East and southern Europe
- Kazakhstania (Most of North America, Greenland, northwestern Ireland, Scotland)
- Laurentia (most of North America, Greenland, northwestern Ireland, Scotland)
- Siberia (Russia, Asia north of Kazakhstan and China
+ several microcontinents (atlantic canada, northeastern cost of US)
Describe the Late Cambrian Paleogeography
- polar regions mostly ice free
- Epeiric seas (light blue) covered parts of continents Highlands in NE Gondwana, eastern Siberia, central Kazakhstania
- Eastern Laurentia was a passsive continental margin (minimal plate tectonic activity)
Describe the Late Ordovician Paleogeography
- Gondwana moved south, crossed south 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
- Siberia and Kazakhstania moved from southern tropical to northern temperature latitude
What is the characteristic of Laurentia during this time that led to “drowing” of continents (sea level going up and down)
Laurentia was generally low relief (flat) during Paleozoic
- broad, gentle warping of the continent created arches (high areas of thin sediment deposiiton) and basins (low areas of thick sediment deposition)
What is a Cratonic Sequence? What two processes can it show
It is a large scale 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 (mud sized particles) 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 > offshore is on top of nearshore
(bottom up: land, sandstone, shale, limestone)
What does facies mean (ex. limestone facies, shale facies, sandstone facies)
“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
*near shore is on top of offshore
(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) - progressive migration of offshore facies towards the craton over time
They are Cambrian rocks (came from the Cambrian period)
- most of the sandstone = lower cambrian, most of the shale = middle cambrian, most of the limestone = upper cambrian
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
- deposition of marine sediments on passive shelf areas of Appalachian and Cordilleran borders of the craton
- tropical climate caused erosion of craton
(transgressive phase of the Sauk Sea began in the Middle Cambrian)
What was the Tippecanoe Sequence? When was it?
Oldovician-Silurian
Equator shifted > North America was rotating counterclockwise
Sauk Sea regressed during the Early Ordovician > high erosion of exposed carbonates > unconformity between the Sauk and Tippecanoe sequences
Transgression began again in Middle Ordovician > deposition of sandstone, widespread carbonates (limestone and dolostone) > great fossils
(Regression again during the Late Silurian)
What is the world’s largest trilobite and where was it found?
Isotelus rex
- mid-late Ordovician
- found in tyndall stone near churchill, Manitoba
Where can Ordovician Tyndall Stone be found?
Gillis Quarries in Manitoba
What are reefs? What were the first reef builders and what are they today?
They are limestone structures made by living organisms
- first skeletal 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 nearly parallel to the shoreline
What are the calcium-carbonate secreting organisms in the reef that deposit limestone?
Corals, brachiopods, stromatoporoids, bryozoans
Describe the Silurian Paleogeography of North America (aka what developed at this time?)
Development of reefs:
- warms, shallow marine environment within 30 degrees north or south of the equator
- barrier reefs can cut off water from the open seas > results in evaporation of seawater, deposition of evaporites and evaporite minerals (ex. Halite = table salt)
When did reefs develop?
Silurian period
Explain how evaporite sedimentation works
In a lagoon, evaporation produces a dense brine that sinks and forms a thick evaporite deposit
Shallow sill impedes the outflow of dense brine from the basin
Inflow of seawater replenishes water lost by evaporation
(check diagram in photos)
What makes up a reef complex and in what kind of environment are they found?
Reef complex = back reef (side of lagoon/land) , fore reef (side of ocean), and a flat
In warm tropical waters
What were the 2 cratonic sequences during the Early Paleozoic Era
Sauk & Tippecanoe sequences
