synlinje

Synlinje is a term used in geology in some Scandinavian contexts as the equivalent of the English term syncline. In this usage, a synlinje denotes a trough-shaped fold in layered rocks, in which the strata dip toward an axis that runs roughly along the center of the structure. The youngest rocks are typically found near the core, with progressively older rocks toward the limbs. The name stems from a linguistic root meaning “together” and “slope,” and the term may be spelled as synlinie, synlinje, or synklinal in Norwegian and Danish texts, reflecting regional orthography.

Formation and occurrence: Synlines form under compressional tectonics when crust is shortened, and regional folding associated with orogenic belts redistributes rock layers into trough-like structures. They can vary in scale from small outcrop folds to large, regional features, and they may be symmetrical or asymmetrical, sometimes showing complex layering due to subsequent deformation or faulting. In cross-section, the axis of a synlinje is the line along which curvature is greatest, and the beds dip toward this axis.

Identification and study: In the field, geologists identify synlines by mapping the orientation and vertical sequence of rock layers, noting that younger strata tend to lie toward the center of the fold. Structural restoration methods and balance line techniques are used to infer original positions of the layers before deformation. Synlines are commonly discussed alongside anticlines (arch-shaped folds) and other structural features when describing the tectonic history of an area.

See also: anticline, fold, geological structure, tectonics.