Syncline

In structural geology, a syncline is a fold with younger layers closer to the center of the structure. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed smaller folds. Synclines are typically a downward fold, termed a synformal syncline (i.e. a trough); but synclines that point upwards, or perched, can be found when strata have been overturned and folded (an antiformal syncline).

Characteristics

On a geologic map, synclines are recognized by a sequence of rock layers that grow progressively younger, followed by the youngest layer at the fold's center or hinge, and by a reverse sequence of the same rock layers on the opposite side of the hinge. If the fold pattern is circular or elongate circular the structure is a basin. Folds typically form during crustal deformation as the result of compression that accompanies orogenic mountain building.

Notable examples

• Powder River Basin, Wyoming, U.S.A.
• Sideling Hill roadcut along Interstate 68 in western Maryland, USA, where the Rockwell Formation and overlying Purslane Sandstone are exposed.
• Western Lake Superior, which occupies a basin created by the Midcontinent Rift System
• Saou, a commune in the Drôme department in southeastern France
• The Catlins, an area in the southeastern corner of the South Island of New Zealand

Gallery

• 
  Syncline exposed in Sideling Hill roadcut
• 
  Snow-dusted syncline in Provo Canyon, Utah.
• 
  Road cut near Fort Davis, Texas showing a syncline.
• 
  Rainbow Basin Syncline in the Barstow Formation near Barstow, California.
• 
  Syncline in the lower parking lot of Calico Ghost Town; note ductile folding at base, brittle above.
• 
  Synclinal fold in Silurian Wills Creek Formation or Bloomsburg Formation at Roundtop Hill (Maryland)
• 
  East wall of Bear Valley Strip Mine, near Shamokin, Pennsylvania
• 
  Syncline in Navajo Sandstone, Upheaval Dome, Canyonlands National Park, Utah.

See also

• Anticline
• Homocline
• Monocline
• Ridge-and-valley Appalachians — With good bird's eye photo of a range of the types