Historical Geology 102
Paleozoic - Appalachian Orogeny & Cyclothems
Phanerozoic Eon
570 million years - present
More complete rock record than the Precambrian
Divided into three Eras
Paleozoic Era: 542 - 251 m.y.
Mesozoic Era: 251 - 65.5 m.y.
Cenozoic Era: 65.5 m.y. - present
Paleozoic Periods
Permian Period: 299 - 251 m.y.
Pennsylvanian Period: 318 - 299 m.y.
Mississippian Period: 359 - 318 m.y.
Devonian Period: 416 - 359 m.y.
Silurian Period: 444 - 416 m.y.
Ordovician Period: 488 - 444 m.y.
Cambrian Period: 542 - 488 m.y.
Geologic Time Scale
Geologic events in North America do not match the standard time scale very well.
Geologic Time Scale is based on European geologic events.
Sequence - major, informal lithostratigraphic units covering large areas and separated by periods of erosion.
Cambrian Period
542 - 488 m.y.
Beginning based on appearance of hard-body parts in the fossil record.
All earlier fossils are soft-body parts.
Tommatian Stage - time unit within the Cambrian Period which marks the first appearance of hard-body parts.
Appalachian Orogeny
The Appalachian Mountains formed as the result of 3 major orogenic events
Taconic Orogeny
Acadian Orogeny
Allegheny Orogeny
Taconic Orogeny
Beginning of Paleozoic - eastern margin is a passive margin
Area of deposition during Sauk Sea Transgression
Middle Ordovician - subduction zone develops due to closure of Iapetus Ocean
Start of the Taconic Orogeny
Late Ordovician - well developed volcanic chain
Western flank of volcanic chain - large clastic wedges
Sediments eroded from the Taconic highlands
Coarse sediments in the east part of the wedge - finer sediments to
the west.
Acadian Orogeny
N. America and Baltica began convergence in the Silurian
Major mountain building episode
NE portion of continent - Newfoundland, Greenland into Scotland and Norway
Laurentia + Baltica = Laurussia
SE margin - ocean-continent collision
Allegheny Orogeny
Closure of the ocean between Laurussia and Gondwanaland
Collision of the two continents results in deformation along the southern and eastern margin of N. America
Ouchita Orogeny
Ancestral Rockies
Pangaea
Formation of Pangaea begins in the Pennsylvanian Period
All of the major continental land masses collide together to form a supercontinent. (Allegheny Orogeny in North America)
Pennsylvanian
Absaroka Sequence - Alternating marine and non-marine deposition
Transgression - Regression
Deposition during a single transgression and regression is called a cyclothem
Typical cyclothem in Illinois has 10 units.
Cyclothems
Lower units are non-marine deposits - Coal Beds - Underclay - Fresh water limestone - Sandstone
Upper units are marine deposits: - Limestone - Shale
Extensive deposits covering large areas from Kansas to New York
World-wide occurrence of cyclothems
At least 50 cyclothems are known during this time period.
What causes sea level to change?
Eustasy
Eustasy - sea level changes
Changes in sea level result in transgression or regressions.
Causes of eustasy:
1) Tectonic Activity
2) Isostasy
3) Glaciation
Antler Orogeny
Same time as the Acadian Orogeny
Western margin of N. America - subduction zone develops
Volcanic arc develops initially
Inland thrust faulting results in the formation of the Antler Mountains
Begins in the Devonian - continues into the Pennsylvanian
Sonoma Orogeny
Collision of island arcs with Laurussia along the southwest margin of the continent.
Additional Resources
Paleogeography Maps
The following are a series of incredible maps researched, drawn and copywrited by Dr. Ron Blakey at Northern Arizona University.
Permian Paleogeography
- Global - 260 m.y.
- North America - 260 m.y.
- North America - 275 m.y.
- Global - 280 m.y.
- North America - 290 m.y.
Pennsylvanian Paleogeography
- Global - 300 m.y.
- North America - 300 m.y.
- North America - 315 m.y.
Mississippian Paleogeography
- North America - 325 m.y.
- Global - 340 m.y.
- North America - 345 m.y.
Devonian Paleogeography
- North America - 360 m.y.
- Global - 370 m.y.
- North America - 385 m.y.
- Global - 400 m.y.
- North America - 400 m.y.
Silurian Paleogeography
- North America - 420 m.y.
- Global - 430 m.y.
- North America - 430 m.y.
Ordovician Paleogeography
- Global - 450 m.y.
- North America - 450 m.y.
- Global - 470 m.y.
- North America - 470 m.y.
- North America - 485 m.y.
Cambrian Paleogeography
- Global - 500 m.y.
- North America - 500 m.y.
- North America - 510 m.y.
- Global - 540 m.y.
Additional paleogeographic maps and animations can be found at the PALEOMAP Project by Christopher R. Scotese.