Erosional trap regime

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

Definition

Erosional traps are those in which trap boundaries occur along contacts between erosional surfaces and underlying or overlying reservoirs.

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: Stratigraphic traps

Regime: Erosional traps

Form as a result of erosional processes

Class: 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.

Subclass: Regional subcrop

Uniformly or gently dipping reservoir bed beneath an unconformity. Top seal is provided by postunconformity beds; bottom seal is provided by sealing units beneath reservoir.

Subclass: Paleostructural subcrop

Folded and/or faulted reservoir beds beneath postdeformation unconformity.

Reservoir distribution and trap boundaries are controlled by preunconformity deformation and subsequent erosion.

Class: Erosional relief traps

Closure provided by topographic relief beneath an unconformity.

Subclass: Buried hill

Top-seal closure created by positive erosional relief of reservoir beneath a sealing unconformity surface.

Subclass: 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

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: Erosional traps

Class: Truncation traps

Subclass: Regional subcrop

Superfamily: Nonmarine erosional surface

Family: Sequence-boundary unconformity

Reservoir variety: Marine sandstone subcrop

Seal variety:

Top: Marine transgressive shale above unconformity and marine shale above sandstone.

Bottom: Marine shale beneath sandstone

Subclass: Paleostructural subcrop

Style: Complex fold-fault subcrop

Superfamily: Nonmarine erosional surface

Family: Sequence-boundary unconformity

Subfamily: Postcompressional fold-fault unconformity

Reservoir variety: Multiple truncated marine sandstones

Seal variety:

Top: Postunconformity marine shale

Bottom: Underlying marine shale</list-item></list-item></list-item></list-item></list-item></list-item>

Class: Erosional relief trap

Subclass: Buried hill

Superfamily: Nonmarine erosion surface

Family: Sequence-boundary unconformity

Subfamily: Local differential erosion

Reservoir variety: Basement igneous complex

Seal variety: Marine shales above unconformity

Subclass: Truncation-edge traps

Superfamily: Marine erosion surface

Family: Submarine canyon or gorge trap

Superfamily: Nonmarine erosional surface

Family: Channel-relief or valley-edge relief traps

See also

• Stratigraphic trap system
• Depositional trap regime
• Diagenetic trap regime

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