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.
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.
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