Sevier & Laramide OrogeniesSevier & Laramide Orogenies
The N
orth Am
erican Cordillera
Cordilleran StructureCordilleran Structure
Orogenic SequenceOrogenic Sequence
The Orogenic BeltThe Orogenic Belt
Propagation of Thrust BeltsPropagation of Thrust Belts
““Decollement”Decollement”
Foreland BasinsForeland Basins
Foreland
Orogen
Basin
Sevier OrogenySevier Orogeny
170 to 80 Million years ago170 to 80 Million years ago
Sevier: horribly complexSevier: 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: oversimplifiedSevier: oversimplified
Sediments in the Foreland BasinSediments 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 OrogenyLaramide Orogeny
80 to 40 Million years ago80 to 40 Million years ago
Sevier: another lookSevier: another look
Laramide to the eastLaramide to the east
Laramide Involves Basement!Laramide Involves Basement!
http://element.ess.ucla.edu/publications/1998_Laramide/RMF_velocity_movie.gif
Follow this link for a neat movie!Follow this link for a neat movie!
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