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.

See: reservoir,  seal,  source rock,  stratigraphic trap,  trap

2. n. [Geology]

A reduction in bed thickness resulting from onlapping stratigraphic sequences.

See: onlap,  source rock