Stratigraphic
Evolution of Erosional-to Levee- Confined Channel - Complexes, Offstore West
Hadler-Jacobsen, Frode1,
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