Late Paleozoic (midterm 2) Flashcards
What are the 3 periods in the Late Paleozoic Era
Devonian (416-359 Ma)
Carboniferous (359 - 299 Ma)
> Mississippian and Pennsylvanian
Permian (299 - 251 Ma)
What are mobile belts?
(aka orogenic belts or orogens) - they are elongated zones of Earth’s crust that have undergone significant structural deformation, often associated with mountain building and plate tectonics
Explain the Appalachian mobile belt evolution from the Neoproterozoic/early Ordovician to the middle Ordovician
At the start (Neoproterozoic/early Ordovocian) we have a spreading centre and a divergent plate boundary which helped widen the lapetus ocean
- one side is Laurentia (passive margin)
- the other side is Baltica (Europe) (also passive)
Then we have oceanic-continental convergent plate boundaries on both sides (both margins/sides are now active
*check diagram in photos
What is a clastic wedge?
A clastic wedge is a large accumulation of mostly detrital sediments deposited in a basin next to uplifted areas
Describe the sediments of the Taconic Highlands and Queenston Delta Clastic Wedge
In the Queenston Delta wedge, sediments are thickest and coarsest near the Taconic Highlands and thin away from them - the wedge eventually grades into a carbonate cratonic facies
What are the sea level trends during the late paleozoic?
Sea levels are going up and down but by the end of the Paleozoic they’re pretty constant and close to modern levels
In what geologic period does Pangaea form?
Permian (late Paleozoic)
Give a summary of the Late Paleozoic Paleogeography (environment and climate)
Major glacial cycles occurred over much of Gondwana during the Late Mississippian (Carboniferous) and early Permian
A variable global climate during the Late Paleozoic is suggested by large coal, evaporite, and tillite deposits around the world
Pangaea formed by the end of the Permian, dramatically altering ocean and atmosphere circulation patterns
Explain the Paleogeography during the late Devonian Period (mountains, sea, oceans, etc.)
Mountain building & global sea level rise
Southern lapetus ocean narrowed between Laurasia & Gondwana
Acadian Orogeny built mountains along eastern Laurasia
Antler Orogeny built mountains in western Laurasia
Erosion of highlands = red fluvial sediments in Europe & eastern US
What is a modern day example of rocks that formed during the late Devonian Period
The Catskill Delta, eastern US
- Old Red Sandstone
Explain the Paleogeography during the early carboniferous period (continent movement, mountains, seas)
Gondwana moved over South Pole
> Extensive continental glaciers
Sea levels rose and fell
Gondwana collides with Laurasia, setting off orogenies worldwide
Explain the Paleogeography during the late carboniferous period (mountains, etc.)
Mountain building where Gondwana & Laurentia collide
Ancestral Rock mountains formed
Extensive coal swamps common worldwide *source of most of the world’s coal supply today
Explain the Paleogeography during the late Permian (continents, ocean, mountains, etc.)
Pangea was fully assembled (Laurasia and Gondwana together)
Panthalassa ocean (global - encircles pangea)
Water temperatures stable from increased circulation
Size of supercontinent plus high mountains formed arid (dry) & semiarid climates in the interior *produced extensive red beds & evaporites; coal formation restricted
What were the 3 main environmental/climate periods during the late Paleozoic Evolution of North America?
- Extensive shallow marine carbonate deposition
- Large coal-forming swamps
- dry, evaporite-forming terrestrial conditions
The sea level changes during the lage paleozoic evolution of north america were caused by what?
- glaciers on Gondwana
- tectonism from Pangaea assemblage
Explain the Kaskaskia Cratonic Sequence
Began accumulating as the Kaskaskia Sea transgressed (rose) over a low-relief North American craton during the Middle Devonian and Late Mississippian
The basal deposits are well-sorted quartz sandstones (eroded sediments from Appalachian highlands to east)
Explain how the Appalachian Highland Erosion connects to the Kaskaskia cratonic sequence
The Kaskaskia sequence is made up of rocks from the eroding highlands of the Appalachian mobile belt, exhumed Cambrian and Ordovocian sandstones from the flanks of the Ozark Dome, and exposures of the Canadian Shield in the Wisconsin area
In some small areas, the Kaskaskia consists of black shales and carbonates (limestones) created by extensive reef-0building episodes
Explain reef development in Western Canada (middle and late devonian)
Middle and Late Devonian reef deposits in western Canada, formed as the Kaskaskia Sea transgressed, are major reservoir rocks for petroleum
As the reefs grew and restricted the flow of sea water by the end of the Middle Devonian, extensive evaporite deposits formed - more than 50% of the world’s potash (potassium-rick material used in fertilizers) comes from these evaporites
Explain how black shale deposits came about during the Devonian period
Mid to late Devonian: deposition of shales replaced carbonate-evaporite deposition in parts of North America
End Devonian: widespread black shale formation over much of the North American craton
Fossils are quite rare, though some contain conodonts
*black shales contain a lot of organic matter - can turn into oil and gas - very valuable
What is the significance of the New Albany Shale
- example of black shale outcrop
- how these black shales formed is not exactly known
- formed on the anoxic (low oxygen) bottoms of shallow seas
> Low oxygen conditions to prevent the decay of the organic matter - which is what allows it to turn into something valuable like a hydrocarbon - bioturbation and fossils extremely limited
- large deposits of uranium and petroleum
What is fracking?
Injection of fluids into the subsurface to fracture the rocks that have those hydrocarbons in it - gas and oil trapped inside the shale and we break it apart to be able to release it → drill a well and blast water into this layer, causing fractures in it to release the hydrocarbons
How did the Kaskaskia cratonic sequence end?
During the early/mid Carboniferous period
- Kaskaskia sea regressed (fell) from the craton, exposing it to weathering and erosion
- the end of the Kaskaskia sequence is marked by a craton-wide unconformity (entire craton is covered by an erosional sequence)
When was the Absaroka Cratonic sequence?
During the Pennsylvanian (late Carboniferous) and throughout the Permian period
What are the mountain building episodes included in the Absaroka cratonic sequence?
The Ouachitan and Alleghenian episodes
What process is tied into the evolution of the cratonic sequences
They are tied into transgressions and regressions of the sea level
Explain the Pennsylvanian Paleogeography of NA (which sequence and how does the rock thickness vary / what changes from the east to the west)
Absaroka sequence from early Pennsylvanian (late Carboniferous) to early Jurassic
- lower-most rocks of Absaroka sequence are largely confined to craton margins
Rocks change laterally:
- thickest are in the east and southeast, near the emerging highlands of the Appalachian and Ouachita mobile belts, and they are thin westward onto the craton
- nonmarine detrital and coals in the east to marine detrital and carbonates in the west
Explain the environment / vegetation characteristics by the mid Pennsylvanian (308 Ma)
- terrestrial plants evolved to a point where trust forests were developed
- presence of extensive, lush, swampy forests characterized North America during the Pennsylvanian period
- lots of vegetation material (which ended up giving us coal deposits)
- rocks are characterized by repeating patterns of alternating marine and nonmarine strata which are called Cyclothems
Much of Earth’s coal formed during the ______________
Late Carboniferous
> because at this time, large wetlands covered large areas of Earth
What is the significance of coal? How is it mined?
- provides much of the electricity for the US
- is important in steel production
It is mined underground and on the surface through exposed seams
What are Cyclothems?
- repetitive pattern of marine and non-marine environments (and sediments)
- represent transgressive-regressive cycles separated by unconformities
What is an idealized cyclothem?
- non-marine unit at base
- coal swamp
- marine unit on top (near shore and off shore)
*often disrupted by erosion
*look at diagram in photos
Explain the Cyclothem-Producing Environments
- lots of swamps with coal deposits that are very carbon rich
- transgressing sea (marine deposition) moving to coal swamp which then moves onto nonmarine deposition
- Cycle will repeat itself with sea level falling and rising again
What are the 5 stages or coal (from lower to higher grade)
Peat > Lignite > Sub-bituminous > Bituminous > Anthracite
(needs lots of time and pressure and heat to move through these stages)
Explain the 4 stages of coal formation
- Peat stage: plants grow, die, accumulate > low oxygen environment to keep the plant remains, preserved plant remains > form carbon rich peat which is a light moisturized material
- Lignite stage: with time, peat is buried > some water removed and compacted carbon > increase in time and pressure turns peat to lignite (aka brown coal)
- Bituminous coal stage: increasing time and pressure > further reduction in moisture > lignite turns to bituminous coal > more carbon, more energy if you burn it = more valuable deposit
- Anthracite stage: highest grade coal > highest carbon, lowest moisture, burns cleanest (metamorphic processes because of the amt of heat required and needing more than just burial)
What environment is needed for coal formation?
Lots of vegetation and oxygen (swamps and wetlands)
- lots of turnover of plant materials
What are the factors that impact coal formation?
- organic material
- environment (low O)
- temperature & pressure (deep burial)
- time
What is the percentage of each type of coal that is found in the USA (and basically the same for Canada)
Anthracite: 1% (most rare, needs most time and heat and pressure to form)
Bituminous coal: 48%
Subbituminous coal: 34%
Lignite: 17%
What is the significance of the Middle Absaroka Reefs?
The Absaroka Sea slowly retreated from the craton so that by the Early Permian, the sea extended from Nebraska to west Texas > extensive evaporites developed (deposition of salts)
*another example of just how many economically important deposits were happening during this time
How was the rocky mountain uplift different from most other mountain building events so far
It involved intracratonic deformation (rock deformation that occurs within the stable interior of a continental plate (craton), usually far away from active plate boundaries
whereas typically we’ve seen mountain building with mobile belts and orogenies (collision of two continents)
When and where did the rocky mountain uplift occur?
Occurred in North America during the Pennsylvanian (late Carboniferous) period
What did the rocky mountain uplift maybe result from? Explain what formed and occurred because of the uplift
The uplift may have been a result of the collision of Gondwana with Laurasia along the Ouchita mobile belt
Ancestral rockies formed > from the uplift of the craton centre, faulting happening through basement rock and some uplift along it
Precambrian igneous and metamorphic rocks and overlying Paleozoic sedimentary rocks were uplifted and eroded > red arkosic sands and conglomerates were deposited in surrounding basins
Name the 3 mobile belts that we talk about happening during this time period
Cordilleran Mobile Belt
Ouachita mobile belt
Appalachian Mobile belt (formation of Laurasia)
What are the main points about the Cordilleran mobile belt?
Oceanic-continental convergence, volcanic arc, continental shelf
Antler Orogeny: the ancestral rockies
> Antler Highlands
During the late Devonian - Early Mississippian
What are the main points about the Ouachita mobile belt (explain the process)
Proterozoic - Early Mississippian:
- passive margin (North America and oceanic crust)
Early Mississippian:
- now continent-continent margin (North America and Gondwana)
- uplift to form Ouachita mountains
Pennsylvanian-Permian:
- continued collision creating mountain ranges
What do we end up with because of the Appalachian Mobile belt?
- erosion of the highlands created the old red sandstone
- on one side of the Acadian-Caledonian highlands is the Catskill Delta clastic wedge (what we have in North America)
- on the other side is the old red sandstone that we see in England
*Like twin deposits that are now very far apart
