Geologic History and Petroleum Systems of the Eastern Deepwater Niger Delta

Michael J. Roberts
ChevronTexaco Energy Technology Company, Bellaire, TX

The Eastern Deepwater Niger Delta is bounded laterally by the Cretaceous age Charcot seamount trend on the west and the early Miocene Cameroon Volcanic Chain on the east. The region is partitioned into major strike parallel belts reflecting the structural growth history and fill sequence of the basin. Immediately outboard of the present day shelf edge, a late Oligocene to early Miocene fold and thrust belt is observed. This paleofold belt marks the basinward limit of structuring during this time. Turbidite deposition was strongly influenced by the growing structural front while outboard of the fold belt, unconfined sedimentation occurred. These distal early Miocene sediments are observed however, to onlap the emergent Charcot volcanic peaks toward the west. On the east, active uplift and emplacement of the northeast trending Cameroon chain created a counter regional dip gradient which served to divert sedimentation patterns toward the southwest.

At the end of middle Miocene time (~10 ma), the structural limit of the basin shifted abruptly southward, coincident with a major ramp in the basal detachment surface and the development of the outer toe-thrust belt which structured the earlier deposited unconfined turbidites. The eastern margin of the basin developed a strong left-lateral strike slip component as the advancing structural front impinged on the uplifted Cameroon chain. From late Miocene to Recent, the region has experienced structural readjustment and strongly confined depositional patterns. Maturity modeling has demonstrated a basinward sweep of the oil window within the early Tertiary source rock interval during this time.