Anticline

Anticline in a road cut-out near Fort Davis, TX. Cliff Cuffey, geologist, photographed by Eric S. Kounce on October 29, 2006.

Anticline with syncline visible at far right- USGS. Note the man standing before the formation, for scale.

In structural geology, an anticline is a fold that is convex up or to the youngest beds.

On a geologic map, anticlines are usually recognized by a sequence of rock layers that are progressively older toward the center of the fold. The strata dip away from the center of the fold.

If an anticline plunges (i.e., is inclined to the earth's surface), the surface strata will form Vs that point in the direction of plunge. Anticlines are typically flanked by synclines although faulting can complicate and obscure the relation between the two. Folds typically form during crustal deformation as the result of compression that accompanies orogenic mountain building.

Anticline terminology

Any fold whose form is convex upward is an antiform, and most antiforms are anticlines.

Antiforms are small, generally non-mappable anticlines, whereas a fold is referred to as an anticline if it is of mappable size. This of course depends on the scale of the map, but a rule of thumb is that an antiform is of outcrop scale and an anticline is bigger.

A large-scale anticline that plunges in all directions to form a circular or elongate structure is a dome. Domes are generally formed from one main deformation event, or via diapirism from underlying granitic intrusions of salt domes.

An anticline which plunges at both ends is termed a culmination, and is typically formed from multiple deformations, or superposition of two sets of folding.

An elongate dome which developed as the sediments were being deposited is referred to as a pericline.

An anticlinorium is a series of parallel anticlinal folds on a regional domed structural feature. Example include the Late Jurassic to Early Cretaceous Purcell Anticlinorium in British Columbia[1] and the Blue Ridge anticlinorium of northern Virginia in the Appalachians [2].

Economic significance

Anticlines, culminations and structural domes are favored locations for oil and natural gas drilling; the fuel's low density causes it to migrate upward to the highest parts of the fold, until stopped by an impermeable layer.

Periclines are important focal points for pooling of hot, metal-laden formational brines, which can form manto ore deposits, Irish-type lead-zinc deposits and uranium deposits, amongst others.

Culminations in folded strata which are cut by shears and faults are favoured loci for deposition of saddle-reef style lode gold deposits. Here, hot hydrothermal fluid pools in the trap formed by the anticline and forms the gold deposit.

References

• Davis, George H., Reynolds, Stephen J., 1996. Structural Geology of Rocks and Regions: John Wiley & Sons, Inc., New York. ISBN 0-471-52621-5
• Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution. 2nd ed. Belmont: Wadsworth Publishing Company, 1997. ISBN 0-314-09577-2