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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Sequence Stratigraphic Framework
of Neogene Strata in Offshore Nigeria
By
The western portion of the Nigerian continental margin
is underlain by continental and transitional crust. It exhibits
stable to moderately unstable progradation and is characterized
by a well-developed shelf-slope break. Systems
tracts
are similar to those described by Vail for stable
progradational margins.
In contrast, strata off the central portion of the Nigerian
coast, in the vicinity of the Niger Delta, are underlain by
oceanic crust. Systems
tracts
are similar to those in
Neogene strata of the offshore Gulf of Mexico. The
continental margin exhibits highly unstable progradation.
Large growth faults, toe-thrusts and well-developed shale
diapirs are present. The shelf/slope break is commonly not
well-developed. Instead, a ramp is usually observed. In some
places, this ramp is cut by large growth faults that define the
shelf margin.
Lowstand basin floor fans in both areas are defined by a
well-developed upper reflection. This reflection downlaps
along the sequence boundary or abuts against the downthrown
side of a growth fault surface. The lowstand slope
fan contains channel complexes characterized by chaotic
bedding with small bright spots and less common large
channels, which exhibit concave-upward reflections. Most
of the slope fan systems
tract is comprised of discontinuous
to semi-continuous subparallel reflections. In the western
portion of the study area, slope fan deposits commonly
pinch out at or near the shelf margin. Sand-rich facies
(suggested by amplitude anomalies) are developed immediately
downdip of major canyon cuts and deposition occurred
largely from point sources. In contrast, contemporaneous
shallow-water facies are developed in slope fan
systems
tracts
off the central portion of the Nigerian coast. Deposition
occurred along a line source.
Large amplitude anomalies in the lowstand prograding
wedge suggest well-developed sheet sands are present off
both western and central portions of the coast. These sands
are present in both shallow-water (interpreted as delta front
facies) and deepwater deposits (interpreted as shingled turbidites). The transgressive and highstand systems
tracts
are usually very thin.
Different exploration strategies are appropriate for
each systems
tract off both the western and central portions
of the Nigerian coast. The best plays off the central portion
of the Nigerian coast are probably structural traps (this
includes updip pinchouts) whereas hydrocarbons may
occur in both structural and stratigraphic traps along the
west coast of Nigeria.
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