Erosional trap regime

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Traps, trap types, and the petroleum system
Chapter Classification of exploration traps
Author Richard R. Vincelette, Edward A. Beaumont, Norman H. Foster
Link Web page
Store AAPG Store


Erosional traps are those in which trap boundaries occur along contacts between erosional surfaces and underlying or overlying [[reservoir]s.

Classes and subclasses

Three trap classes have been identified, based on the geometry of the reservoir beds in contact with the unconformity surface. The hierarchical structure and definitions are shown below.

System Regime Class Subclass
Stratigraphic traps Erosional traps; Form as a result of erosional processes Truncation traps; Up-dip reservoir boundary created by truncation of a reservoir beneath an unconformity, followed by deposition of sealing unit on top of an unconformity. The unconformity surface provides top seal, but closure usually requires the presence of depositional or tectonic side and bottom seals beneath the unconformity. Regional subcrop; Uniformly or gently dipping reservoir bed beneath an unconformity. Top seal is provided by superunconformity beds; bottom seal is provided by sealing units beneath reservoir.
Paleostructural subcrop; Folded and/or faulted reservoir beds beneath postdeformation unconformity. Reservoir distribution and trap boundaries are controlled by prehiatus deformation and subsequent erosion.
Erosional relief traps; Closure provided by topographic relief beneath an unconformity. Buried hill; Top-seal closure created by positive erosional relief of reservoir beneath a sealing unconformity surface.
Truncation edge; Side seal provided by truncation of a reservoir against later erosional valley, channel, or gorge wall and subsequent deposition of sealing beds in valley, channel, or gorge.


Families of the erosional trap regime have been established based upon the genesis of the unconformity surface that controls the trap boundaries. Two superfamilies are recognized: nonmarine erosion surfaces and marine erosion surfaces. Within these superfamilies, more detailed family classifications can be established. Where desired, trap varieties can be utilized to provide more details of reservoir and seal genesis. The outline below shows the superfamilies, families, and subfamilies of the subclass gorge-edge traps.

Regime Class Subclass Style Superfamily Family Subfamily Reservoir Variety Seal variety
Top Bottom
Erosional traps Truncation traps Regional subcrop Nonmarine erosional surface Sequence-boundary unconformity Marine sandstone subcrop Marine transgressive shale above unconformity and marine shale above sandstone Marine shale beneath sandstone
Paleostructural subcrop Complex fold-fault subcrop Nonmarine erosional surface Sequence-boundary unconformity Postcompressional fold-fault unconformity Multiple truncated marine sandstones Superunconformity marine shale Underlying marine shale
Erosional relief trap Buried hill Nonmarine erosion surface Sequence-boundary unconformity Local differential erosion Basement igneous complex Marine shales above unconformity
Truncation-edge traps Marine erosion surface Submarine canyon or gorge trap
Nonmarine erosional surface Channel-relief or valley-edge relief traps

See also

External links

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Erosional trap regime
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