Sinuous Slope Channel Evolution: Insights from 3-D High-Resolution Seismic Data, Piston Coring, and Numerical Modeling of the Western Niger Delta Slope

The modern seafloor and shallow subsurface of the western Niger Delta slope exhibits sinuous submarine channels with multiple phases of evolution. Investigations of these channels using three-dimensional (3D) high-resolution seismic-reflection data, and piston coring offer a rare opportunity to examine a lithologically calibrated submarine channel system. At least three phases of channel development and evolution are related to changes in sediment supply coincident with updip avulsions. The first phase is predominantly incisional and creates a large valley within which the subsequent phases evolve. The second phase creates a wide, low sinuosity channel within the valley. This channel displays fluvial point-bar like accretion and expansion/translation of the meander bends. The third and most recent phase is initiated when drainage from a nearby channel is captured by the valley system. This addition of sediment supply causes a narrowing and downcutting of the channel. This narrowing occurs via deposition along the inner bends of the channel and results in very complex inner levee geometries and architectures, which have been intricately mapped on the 3D seismic data. Piston coring of these inner levees reveal heterogeneous facies, while facies in the channel thalweg consist of coarser grained sands that are often amalgamated.

Grain size distributions from the piston cores were also used as inputs for a three-dimensional Navier-Stokes based numerical model. Particularly important was the inputted vertical grain size distributions obtained from the piston coring. Results from simulations of turbidity currents in this lithologically calibrated model indicate complex interactions between the flows and the channel topography, including secondary flow, return flow from the overbank areas, and velocity maxima within the channel. The deposition and sand and mud within the channel system is highly dependent on these intricate, transient flow processes.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California