ABSTRACT: Sequence Stratigraphic Framework of Neogene Strata in the Niger Delta

PACHT, JORY A., BRUCE E. BOWEN, DAVID J. HALL, and BERNARD L. SHAFFER, Calibre Consulting Services, Inc., Houston, TX, and DONALD DEPEW, Consultant, Houston, TX

The Neogene Niger Delta exhibits unstable progradation. It is characterized by very high rates of sedimentation, large-scale growth faulting, and well-developed shale diapirism. Toe thrusts are present along the outer periphery of the delta. 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. An abrupt transition from shelf to slope facies occurs along these faults.

Systems tracts are similar to those developed in Neogene strata of the offshore Gulf of Mexico. Neogene strata of the Niger Delta are dominated by lowstand systems tracts. A gradual transition from shelf to slope facies is observed in all systems tracts, including the "slope" fan, in which updip shallow water facies are well-developed.

Lowstand basin floor fans show a well-developed upper reflection. This reflection either downlaps along the sequence boundary or abuts against a growth fault surface on the downthrown side. The lowstand slope fan contains channel complexes characterized by chaotic bedding with small (less than half a kilometer) bright spots and rare large channels, which exhibit concave-upward reflections. Most of the slope fan systems tract is comprised of discontinuous to semicontinuous subparallel reflections. Large amplitude anomalies in the lowstand prograding wedge suggest well-developed sheet sands are present. These sands are present in both shallow water (interpreted as delta front facies) and deep water deposits (interpreted as shingled turbidites). The transgressive and highstand systems tr cts are usually very thin and the upper boundary of the highstand systems tract typically displays erosion.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)