--> Abstract: Stratigraphic Evolution of Erosional-to Levee- Confined Channel - Complexes, Offstore West Africa; #90063 (2007)

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Stratigraphic Evolution of Erosional-to Levee- Confined Channel - Complexes, Offstore West Africa

 

Hadler-Jacobsen, Frode1, Michael H. Gardner2, William Shea3 (1) Statoil ASA, Golden, CO (2) Montana State University, Billings, MT (3) Envision Ltd, N/A

 

High-resolution seismic stratigraphic and geomorphic analysis reveals the West African continental margin evolution in a small, source-distant deep-marine setting (20 x 30 km area). Depositional outbuilding of the continental margin by gravity driven processes generates local gradients and seafloor topography that determine cyclic changes in aggradational and degradational patterns. This is manifested in the proportion, distribution, size, shape and orientation of lobe-channel-levee complex (LCLCs) seismic geomorphological elements documented within a threefold seismic stratigraphic hierarchy.

 

Six fourth-order cycles, best resolved within the upper part of the succession, consist of multiple, wedge-shaped and compensating LCLCs up to 20 km wide and 0.25 km thick. These depositional elements show an upward increase in channel-levee and decrease in lobe proportion. This corresponds to an overall upward increase in the degradation:aggradation ratio of fourth-order cycle deposits. Changes in this ratio are used to predict lithology distribution in this source-distant setting, as well as the record of the more source-proximal slope evolution, and the volume and types of sediment transmitted basinward of this site.

 

Reconstruction of deep-marine sedimentary terrains within this stratigraphic hierarchy relates dynamic changes in local gradient and seafloor topography to quantified variations in erosional and depositional channel confinement. These attributes are locally derived and directly extracted from the study area. This reduces uncertainty related to more speculative and often; unknown changes in the shelf staging area, does not require correlating longitudinal sediment pathways across complex and evolving slope topography, and explicitly relates local and longitudinal gradient changes to different scales of erosional and depositional confinement.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California