San Juan terranes San Juan Thrust System

1
San Juan terranes-San Juan Thrust System

• Decatur terrane- Jurassic to early Cretaceous-An
  ophiolite with a younger superimposed arc.
  Overlying clastic marine sequence.
• Imbricate Fault Zone- late Cretaceous-fault
  slices of many different rock types most sheared
  and structurally complex

2
San Juan terranes- San Juan Thrust System

• Constitution Formation- Jurassic to early
  Cretaceous- clastic sequence of volcaniclastic
  sediments with some ribbon cherts, and pillow
  lavas
• Garrison terrane- Permian to early Triassic high
  pressure schist. Occurs as small fault slices
  along one of the thrust faults.

3
San Juan terranes- San Juan Thrust System

• Deadman Bay Terrane- Triassic to early Jurassic-
  ribbon cherts, pillow basalts, and limestones
  Tethyan-fusulinid limstone.
• Turtleback Terrane- Cambrian to early Permian-
  plutonic complex of tonalite and gabbro. Upper
  unit consists of volcanic-arc with some
  limestones Fusulinids are non-Tethyan.

4
San Juan terranes-External Units

• Haro Terrane- late Triassic to early Cretaceous-
  marine sandstone, conglomerates, volcaniclastic
  sediments
• Nanimo Group- late Cretaceous- marine and
  non-marine sandstones, conglomerates, and shale

5
San Juan terranes-Post Orogenic Unit

• Chuckanut Formation- Eocene nonmarine sandstone
  and conglomerate