1999 Abstract: Armentrout et al.
Analysis of Gravity-Flow Depositional Systems from 3-D Seismic Data: Neogene Deposits of the Niger Delta Slope
John
M. Armentrout
Mobil Technology Company, Inc.
P.O. Box 650232
Dallas, TX 75265-0232
Katherine
A. Kanschat
Mobil Technology Company, Inc.
P.O. Box 650232
Dallas, TX 75265-0232
Kristian
E. Meisling
Mobil Technology Company, Inc.
Dallas, Texas
Currently with ARCO Oil and Gas
Plano, Texas
Jerome
J. Tsakma
Mobil
Producing Nigeria, Ltd.
Lagos, Nigeria
Lisa
Antrim
Amoco
Production Company
Houston, Texas
Currently with BP/Amoco
Houston, Texas
Dennis
R. McConnell
Amoco
Production Company
Houston, Texas
Currently Geological Consultant
Houston, Texas
Abstract
Gravity-flow depositional systems of a portion of the Niger delta slope are imaged and documented in seismic amplitude extraction and coherency displays from a large 3-D seismic volume. The displays are extracted immediately above regionally significant sequence boundaries. Interpretation of the 3-D seismic reflection volume demonstrates the strength of combining seismic sequence stratigraphic analysis methodology with the turbidity system architectural element framework.
Each of the gravity-flow systems consists of confined- flow channel-form elements grading down slope into less confined flow, lobe- to sheet-form elements. The Niger slope depositional systems are confined to slope-valley and slope-basin bathymetric lows. The valleys are bounded by densely faulted, structurally complex zones clearly imaged on coherency processed 3-D time slices but poorly imaged on 2-D profiles where they have been previously interpreted as zones of shale diapirism. Restoration of the valley systems suggests that they had very low relief paleo-bathymetric profiles similar to those observed on the present sea floor. Lower slope basins are "piggy-back" basins above toe thrusts linked to deep-seated gravity- driven, extensional failure of the slope.
Each gravity-flow depositional system consists of three architectural segments: (1) upper slope, small-scale channel elements converging down slope into, (2) single- channel and nested-channel elements with linear to sinuous map patterns, grading farther down slope into, (3) slope basin lobe and sheet elements. Three types of channel elements are observed: (1) erosional, (2) erosional- depositional, and (3) depositional. The depositional channel elements have geometries strongly suggestive of channel-levee-overbank complexes, indicating that transport must include turbidity-flow processes. In one case, the gradation from mapped channel to lobe to fan elements occurs over less than 1 km (0.65 mi). Within the sheets, lateral accretion of depositional elements suggests compensation sedimentation composed of amalgamated depositional events.
Mapped amplitude patterns of the sequences suggest switching of the inferred sand-prone depositional system from one slope valley to another through time. This is interpreted to reflect both the lateral shifting of the fluvial sediment supply on the shelf, and the local tectonic modification of valley system bathymetry.
The 3-D seismic reflection volume resolves the depositional systems formed by gravity-flow processes through all mapped sequences of the study area. These depositional systems occur within the stratigraphic interval immediately above seismic sequence boundaries and consist of depositional elements known to occur in other modern and ancient turbidite systems.