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!