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 [[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

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

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

External links

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