Syncline

In structural geology, a syncline is a fold, with younger layers closer to the center of the structure. A synclinorium 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 can be found when strata have been overturned and folded (an antiformal syncline).

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. A notable syncline is Wyoming's Powder River Basin. Folds typically form during crustal deformation as the result of compression that accompanies orogenic mountain building.

A very well exposed syncline is at the Sideling Hill roadcut on Interstate 68 in western Maryland, USA, where the Rockwell Formation and overlying Purslane Sandstone are exposed.

A spectacular example of a perched syncline, the highest in Europe, is Saou, in the Alpine foothills of south-eastern France.

Gallery of Synclines

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  Snow-dusted syncline in Provo Canyon, Utah.

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  Road cut near Fort Davis, Texas showing a syncline.

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  Rainbow Basin Syncline in the Barstow Formation near Barstow, California.

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  Syncline in the lower parking lot of Calico Ghost Town; note ductile folding at base, brittle above.

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  Synclinal fold in Silurian Wills Creek Formation or Bloomsburg Formation at Roundtop Hill (Maryland)

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  East wall of Bear Valley Strip Mine, near Shamokin, Pennsylvania

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  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