Sevier & Laramide Orogenies
The North American Cordillera
Cordilleran Structure
Orogenic Sequence
The Orogenic Belt
Propagation of Thrust Belts
“Decollement”
Foreland Basins
Foreland Orogen Basin
Sevier Orogeny 170 to 80 Million years ago
Sevier: horribly complex
Middle Jurassic: 170 – 160 Million years ago
Late Jurassic: 160 – 155 Million years ago Western Plate Margin Consolidates, accretion of Coast Range Ophiolite Farallon Plate Subduction Begins
Latest Jurassic: 155 – 142 Million years ago Voluminous Arc Magmatism Crustal Shortening
Early Cretaceous: 142 – 110 Million years ago Emplacement of “Mega-Thrust Sheet”
Middle Cretaceous: 110 – 85 Million years ago Onset of rapid shortening and Sevier Orogeny
Sevier: oversimplified
Sediments in the Foreland Basin The diagram shows two diferent kinds of sediments in the foreland basin: Sediment from the west is clastic sandstone and mudstone, eroded from the mountains of the thrust belt. Sediments from the east are shales and marine sediments which developed in a shallow sea. The dotted line shows the migration of sea level back and forth as sediments were deposited.
Laramide Orogeny 80 to 40 Million years ago
Sevier: another look
Laramide to the east
Laramide Involves Basement!
Follow this link for a neat movie!