Synclinorium

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 can be found when strata have been overturned and folded (an antiformal syncline).

On a geologic map, synclines are recognized as 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.

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

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