thumb|A syncline is a fold of rocks with younger rock layers closer to the center of the structure, whereas an anticline is the inverse of a syncline.|right|upright=1.95

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
  • 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
  • Fort Valley, Shenandoah County, Virginia
  • Hondo Syncline in the Picuris Mountains of New Mexico, an example of an overturned syncline
  • Afikpo syncline, Nigeria
  • Table Mountain, South Africa

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File:Sideling Hill cut MD1.jpg|Syncline exposed in Sideling Hill roadcut

File:Provo Canyon syncline.jpg|Snow-dusted syncline in Provo Canyon, Utah

File:Syncline.JPG|Road cut near Fort Davis, Texas showing a syncline

File:Rainbow Basin.JPG|Rainbow Basin Syncline in the Barstow Formation near Barstow, California

File:SynclineCalico.JPG|Syncline in the lower parking lot of Calico Ghost Town; the ductile folding is at the base and the brittle is above.

File:Roundtop Hill outcrop1.jpg|Synclinal fold in Silurian Wills Creek Formation or Bloomsburg Formation at Roundtop Hill (Maryland)

File:Bear Valley east wall.jpg|East wall of Bear Valley Strip Mine, near Shamokin, Pennsylvania

File:Upheaval Syncline campsite.jpg|Syncline in Navajo Sandstone, Upheaval Dome, Canyonlands National Park, Utah

File:The Catlins.jpg|Satellite view of part of New Zealand's Southland Syncline, showing parallel folds running northwest–southeast

File:Wilpena Pound - Aerial View.jpg|Wilpena Pound, a synclinal basin in the Flinders Ranges of South Australia

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See also

  • Homocline
  • Monocline
  • Ridge-and-Valley Appalachians
  • Structural basin

References