Print this page3D Seismic Definition of Pleistocene Sediment Gravity-Flow Depositional Systems, Southeast Niger Delta Shelf to Slope Area, Gulf of Guinea
ARMENTROUT, JOHN M., KATHERINE A. KANSCHAT, JEROME J. TSAKMA, LISA ANTRIM and DENNIS R. McCONNELL
Areally extensive 3D seismic surveys facilitate construction of observationally constrained, high-resolution depositional models. Analysis of a proprietary 3D survey over the southeast Niger delta slope provides examples of deep-water, gravity-flow depositional systems. These systems consist of confined-flow channel-form elements grading downslope into less confined-flow, lobe-form to sheet-form elements. The gravity-flow systems are imaged on amplitude extraction and coherency maps for discrete stratigraphic intervals immediately above regionally significant sequence boundaries. Study of these systems at shallow stratigraphic depths provides high resolution depositional models for interpreting deeper, lower resolution exploration objectives.
The depositional systems appear to be confined to slope-valley topography on the Niger slope. They consist of three architectural elements: (1) upper slope, small-scale channel-form elements converging down slope into, (2) single channel-form and nested channel-form elements with linear to sinuous map patterns, grading further downslope into, (3) slope-basin lens- to sheet-form mapped as lobe-form or fan-form elements. Three types of channel-form elements are observed: (1) erosional, (2) erosional-depositional, and (3) depositional. The depositional channel-form elements have geometries strongly suggestive of channel-levee-overbank complexes and meander-bend lateral accretion complexes. Within the fan-form sheets, lateral accretion of depositional elements suggests compensation sedimentation of amalgamated sheets. In one case, the gradation from mapped channel-form to lobe-form to fan-form elements occurs over less than 2 miles. This gradation is characterized by seismic profile facies of erosional-depositional channel to broad hummock to sheet geometries.
Slope basin depocenters are typically bordered by north-south aligned highly structured "shale-prone masses" and form down-thrown to growth faults and as piggy-back basins behind toe-thrust complexes. The more laterally extensive amalgamated lobe-form geometries within these slope basin settings are considered the primary exploration targets.