Structures In Rocks Topics

• Introduction
• Forces
• Geologic Structures
• Mapping Geologic Structures
• Structures In Virginia Rocks
  1. Coastal Plain
  2. Piedmont
  3. Mesozoic Basins
  4. Blue Ridge
  5. Valley and Ridge
  6. Appalachian Plateaus

Structures In Virginia Rocks (Part 1)

• Virginia has a wide variety of geologic structures, including anticlines, synclines, faults, domes, and basins.  Structures are different in Virginia’s physiographic provinces: Coastal Plain, Piedmont, Mesozoic Basins, Blue Ridge, Valley and Ridge, and Appalachian Plateaus.

Diagram courtesy of the Virginia Division of Geology and Mineral Resources

The Appalachian Plateaus are nearly flat-lying layers.  The Valley and Ridge is made up of folded and faulted sedimentary layers.  The Blue Ridge and Piedmont are underlain by folded and faulted metamorphic and igneous rocks.  The Mesozoic Basins have faults and layers that dip gently toward the west.  Coastal Plain layers dip toward the ocean without much faulting.

Coastal Plain

• The Coastal Plain is underlain by beds dipping gently toward the ocean.  Some faulting is present near the inland edge.  Local uplift and downwarp are also present.

Left: gently dipping bed (Photograph by Robert Whisonant); right: the Chesapeake Bay impact structure (Diagram courtesy of the United States Geological Survey)

The Coastal Plain is underlain by gently dipping beds of sedimentary rock, as shown left at a quarry near Fredericksburg.  Some faults in the Coastal Plain may have been caused by a meteorite that fell to the earth about 35 million years ago, creating the crater in the Chesapeake Bay shown in the right diagram.

Piedmont

• The Piedmont is made up of highly deformed igneous and metamorphic rocks.  Folding and faulting have occurred.

Complex folding in the Piedmont (Photograph by Robert Whisonant)

 The above photograph shows metamorphic deformation in Fairfax County.

 

 

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