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
 * Fort Valley, Shenandoah County, Virginia
 * Hondo Syncline in the Picuris Mountains of New Mexico, an example of an overturned syncline.