--> Abstract: Quantitative Seismic Geomorphology of Miocene Submarine Channel-Levee and Distributary Channel Networks Around Growing Salt-Related Slope Topography, Offshore West Africa, by Ayodeji P. Oluboyo, Dina Vachtman, and Robert L. Gawthorpe; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Quantitative Seismic Geomorphology of Miocene Submarine Channel-Levee and Distributary Channel Networks Around Growing Salt-Related Slope Topography, Offshore West Africa

Ayodeji P. Oluboyo1; Dina Vachtman1; Robert L. Gawthorpe2

(1) Basin Studies Research Group, University of Manchester, Manchester, United Kingdom.

(2) Department of Earth Sciences, University of Bergen, Bergen, Norway.

This presentation focuses on the seismic geomorphologic expression of submarine channel-levee and lobe complexes deposited around growing salt-related slope topography from the Miocene, offshore W Africa. In particular, we analyse distributary channel networks, lobes and splays developed along major sediment fairways on the slope and their location and geometry with respect to developing salt-wall and minibasins topography. We integrate spectral decomposition and RGB blending from horizon and isoproportional slices, with cross-sectional analysis of seismic facies to image key depositional elements such as channel-form HAR’s, levees and distributary channel networks and lobes. Furthermore, image analysis of RGB blended attribute maps has allowed quantification of the plan-form geometry of channel reaches and the branching geometry of distributary channel networks (e.g. bifurcation ratio) within lobes and splays on successive horizon and isoslices. This approach enables the down-fairway changes in channel and lobe architecture to be identified and the stratigraphic evolution to be constrained.

Elongate (linked) salt walls 'capture' and confine major sediment fairways over tens of kilometres and have long-lived, stable entry and exit points related to structural lows along salt walls and between salt folds/diapirs. The structural lows are important, therefore, in allowing transverse-to-structure flow enabling depositional systems to transfer from one mini-basin to another. These transition areas are often marked by major changes in the type of depositional elements present and in the overall geometry and stratigraphic architecture of the turbidite system. Within the transitional areas, the meander belt widths range from 2 - 5km, and there is a general increase in meander widths downstream with a pronounced narrowing at the fairway exit points. Individual channel widths in most of the studied channel-levee systems range from 0.5 - 1.5 km, with sinuosities between 1.2 and 1.8. The distributary channel widths range from 100 - 450m, with average length-to-width ratios >3, and distinctive elongate 'tongue' shaped geometries. Apex angles of the distributary lobes range from 270 - 490, with number of individual 'terminal' distributary channels within each lobe ranging from 11 - 20. Local blocking and diversion, on a kilometre-scale occurs because of salt-cored highs and ‘capture’ by mini-basin and fault hanging-wall lows resulting in sediment 'shadow' zones.