A fold structure with an arch of non-porous rock overlying porous strata (reservoir rock), providing a trap in which oil, gas, or water may accumulate. In Middle East oilfields, large, upright folds occur in thick, competent limestones which extend for many kilometres; fracturing along the crests of the anticlines increases permeability in the reservoir rocks. See petroleum; and natural gas. Compare fault trap; reef trap; stratigraphic trap; structural trap; and unconformity trap.
Subjects: Earth Sciences and Geography.