Syncline

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

Characteristics

On a geologic map, synclines are recognized as a sequence of rock layers, with the youngest at the fold's center or hinge and with a reverse sequence of the same rock layers on the opposite side of the hinge. If the fold pattern is circular or elongate, 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, US
• Sideling Hill roadcut along Interstate 68 in western Maryland, US, where the Rockwell Formation and overlying Purslane Sandstone are exposed
• Forêt de Saou syncline in Saou, France
• The Southland Syncline in the southeastern corner of the South Island of New Zealand, including The Catlins and the Hokonui Hills
• Strathmore Syncline, Scotland
• Wilpena Pound, Flinders Ranges, South Australia

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; the ductile folding is at the base and the brittle is 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
• 
  Satellite view of part of New Zealand's Southland Syncline, showing parallel folds running northwest–southeast
• 
  Syncline of the "Forêt de Saou", Drôme, France

See also

• Anticline
• Homocline
• Monocline
• Ridge-and-Valley Appalachians