Appalachians
• Old Mountains - Young Topography
• Weathered flat
• Uplifted
• Isostatic rebound
Appalachians
• formed the same way as the Himalayas, but compression not active for
over 170 my = erosion........
Appalachians
• Complex prehistory
• 1 billion years ago - continental collision (Supercontinent)
• Grenville Orogeny - old metamorphic roots
• 600 million years ago - rifting = proto-Atlantic forms
Appalachians
• Step 1 = collision with exotic terrane & subduction (Taconic Orogeny)
• Volcanic Mountains - Late Ordovician
• Ocean Basin closing up
Appalachians
• Step 1b -Collision with second exotic terrane (Avolonia) (Acadian Orogeny)
• Collison with large island - Continental Collision
• Middle - Late Devonian
Appalachians
• Step 2 = continental collision (Alleganian Orogeny)
• Late Pennsylvanian - Greatest Uplift - and the last
• Collision with Africa and Europe = Huge Mountains
• Mesozoic => erosion begins to outpace uplift ........ Especially
when uplift/compression stops - Atlantic Ocean opens up
Forming Supercontinents
• Appalachian Orogenies - formation of a supercontinent
• Pangaea - fully formed 280 Ma
• Wilson Cycles - supercontinents form every 500 - 600 Ma
North America - Taconic Orogeny
• Ordovician - Tropical Climate
• Global Sea Level = High
• Complex Marine Communities
• Sandstone, shale, and limestone - southeastern Minnesota
• Ice Age - following mountain building
North America - Acadian Orogeny
• Devonian
• Tropical Environments
• High Sea Level - fish & reefs
• The first forests
North America - Alleghenian
• Pennsylvanian
• Falling Sea Level - Ice Age
• Dense Tropical Forests
• Insects and Reptiles