1. n. [Geology]
A type of stratigraphic trap. The termination by thinning or tapering out ("pinching out") of a reservoir against a nonporous sealing rock creates a favorable geometry to trap hydrocarbons, particularly if the adjacent sealing rock is a source rock such as a shale.
2. n. [Geology]
A reduction in bed thickness resulting from onlapping stratigraphic sequences.