Plate Tectonics Topics

• Introduction
• Theory Development
• Principles of Plate Tectonics
• Plate Tectonics History of Virginia
  1. 1100 m.y.a.
  2. 750-560 m.y.a.
  3. 560 m.y.a.
  4. 560-480 m.y.a.
  5. 480-250 m.y.a.
  6. 250 m.y.a.
  7. 225-200 m.y.a.
  8. 200 m.y.a. to present

Plate Tectonics History of Virginia (Part 4)

560 to 480 Million Years Ago

• As the continental fragments continued to spread apart, a passive margin formed along the edge of Laurentia, the continent that would eventually become North America.

Reconstruction of the world 520 million years ago. Note the widening of the Iapetus Ocean and the position of the future Virginia. At this time, Virginia was on the edge of an island continent known as Laurentia, or "ancient North America". (Image courtesy of the United States Geological Survey)

Between 560 and 480 million years ago, Iapetus continued to grow, and a passive margin developed along ancient North America’s coast.

• Shallow water sediments built up along the continental shelf.

• These sediments can be seen today in the sandstone, shale, and limestone of the Valley and Ridge in Virginia.

The rocks that form today's Natural Bridge were originally deposited in the shallow waters on the margins of Iapetus Ocean. (Photograph by Robert Whisonant)

Natural Bridge, in Rockbridge County, is made up of some of the passive margin sediments that were deposited between 570 and 480 million years ago.

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