Abstract: Seismic signature of an accommodation cycle in the Niger Pleistocene shelf margin delta

SCHWAB, A.M. and M. DALL'ASTA

A relatively "calm" tectonic region of eastern offshore Nigeria was studied with a VHR-2D seismic survey, GUINESS, and also industry-scale surveys, both 2D and 3D. Several VHR lines, parallel to the 2D lines, were used to calibrate the industry-scale seismic; seismic attributes were then mapped using the 3D dataset with a SISMAGE workstation.

An accommodation cycle on the VHR seismic was defined by changes in the angle, continuity, and amplitude of clinoform reflections. A decrease in accommodation shifts clinoforms seaward and they tend to be oblique, convex-down; conversely an increase in accommodation causes high angle sigmoid, convex-up, clinoforms, localized just seaward of prior deposits, which are equivalent to a transgressive surface in a landward direction.

Three, large-scale, accommodation cycles (sequences) were mapped. The shelf-break/shoreline tended to be more (less) linear during an increase (decrease) in accommodation. These regional observations from a relatively "calm" tectonic area suggest that rising shorelines are more wave-influenced, as is the present-day transgression, while the falling shorelines are more fluvially dominated. Future wells in the area will firm-up the details of this concept.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria