Phanerozoic Eon: 542 - 0 Ma

Paleozoic Era: 542 - 251 Ma

Period	Range (Ma)
Devonian	416 - 359
Silurian	444 - 416

Paleogeography and Geology of the Silurian:
Huge reef complexes in many parts of the world

Global oceanic highstand after the big terminal Ordovician regression

In Appalachian Orogen of Laurentia, late flysch and molasse from the Taconic Orogeny, Appalachians erode down to base, resumption of stable margin (carbonate and sandstone) deposits.

In the foreland basin and mid-craton of Laurentia, reefs so big that they allowed evaporation of water in the middle of the basin.

Paleogeography and Geology of the Devonian:
Extremely warm conditions worldwide: evaporites common North and South of 30º.

Continued widespread tabulate-stromatoporoid reef complexes around the world.

In eastern Laurentia, the Taconic Appalachians had worn all the way down by the beginning of the Devonian. No longer molasse deposits, but instead once again stable platform deposits (Helderberg Group, Oriskany Sandstone, etc.).

Collision of Laurentia and Baltica to form Laurussia (sometimes called Euramerica):

• Iapetus Ocean closed in the North, called the Caledonian Orogeny (Silurian-Devonian boundary)
• Rolls southward, compressing Avalonian "peninsula" of Laurentia between Laurentia and Baltica, called the Acadian Orogeny (second of the Appalachian Orogenies: Devonian)
• Molasse of the Caledonian-Acadian Orogeny is called Old Red Sandstone in Europe, and the Catskill Clastic Wedge in North America.

In northern Laurentia, Ellesmere Orogeny (possible collision with one of the Asian blocks)

In western Laurentia, the first of the Cordilleran orogenies:

• The Antler Orogeny (Late Devonian - Mississippian)
• Collision of the Klamath island arc (now part of Nevada, but previously a separate island system) with Laurentia

Towards end of Devonian, CO₂ levels begin to drop:

• Phanerozoic maximum during Cambro-Ordovician
• Drop actually begins during Silurian, but huge drop starting in Late Devonian
• C is being bound up in terrestrial sediment by action of land plants (by soil, by coal deposition, and in plants themsevles)

Major mass extinction even in Late Devonian

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Last modified: 10 January 2008