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.

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