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Neogene Evolution of a Confined Upper Slope Canyon System with Emphasis on Canyon Fill Architecture, Offshore Equatorial Guinea*

Zane Jobe¹and Jim Hewlett²

Search and Discovery Article #50048 (2007)

Posted August 8, 2007

*Adapted from oral presentation at AAPG Annual Convention, with SEPM, Long Beach, California, April 1-4, 2007.

¹Stanford University, Stanford, CA ([email protected])

²Hess Corporation, Houston, TX

Abstract

The slope canyon systems of the Rio Muni Basin, offshore Equatorial Guinea have persisted for more than 80 million years and contain world class hydrocarbon reservoirs. An excellent 3D seismic reflection survey along with borehole, palynologic, and wireline log data beautifully illustrate the aggrading upper slope canyon system ~ 25 km offshore. The slope canyons maintain themselves through syn-depositional faulting and display low sinuosities. During the Neogene, the slope canyons aggraded more than 600 m, while migrating laterally less than 500 m.

Slope canyon fill is characterized by three main depositional elements: 1) thalweg elements that stack upon each other as the canyon aggrades vertically; 2) lateral accretion packages/elements that occur on the inner bends of the low sinuosity canyons; and 3) shingled reflection packages that stack in a down-canyon fashion, usually found just down slope of a knick point.

These three elements are modified by syn-depositional faulting, both small down canyon slumps and large, canyon margin bounding faults that exaggerate the canyon topography and cause the canyons to aggrade rather than migrate. This faulting gives rise to very complex geometries in a dip sense that seem quite simple in a strike sense. The faulting could complicate reservoir connectivity and continuity in similar upper slope canyon systems globally.

Regional Background

(selected figures)

	Regional background: location map of offshore Equatorial Guinea.
	Location map of seismic survey, along with Cretaceous shelf edge, present shelf edge, and Ceiba field.
	Bathymetric map for study area.
	Perspective view of study area, along with seismic lines representative of the shelf edge, slope canyons, and ‘pock marks.’
	Regional stratigraphy.
	NE-SW schematic geoseismic section, with key reflectors and faults.

Faulting

(selected Figures)

	Canyon-parallel faulting.
	E-W seismic line, illustrating down-canyon listric faulting.
	N-S seismic line, illustrating down-canyon listric faulting and “pock marks.’
	NE-SW seismic line illustrate that canyons maintain themselves through faulting/slumping.

Canyon Configuration and Fill Architecture

(selected figures)

Canyon-fill architecture

• Lateral accretion packages (LAP)

• Thalweg

• Shingled canyon fill

	Cross sections of canyons to illustrate their size vs. ‘distality.’
	Modern lateral accretion, illustrated in two N-S seismic lines.
	NE-SW seismic line at different scales illustrating lateral accretion of magenta reflector.
	LAP on seismic line at salmon horizon.
	Reflector hugging base of canyon (thalweg) on two seismic lines.
	Progradation illustrated by shingled canyon fill on E-W seismic line.