Henry W. Posamentier¹

(1) Veritas Exploration Services, Calgary, AB

ABSTRACT: Seismic Geomorphology and Depositional Systems of Deep Water Environments; Observations from Offshore Nigeria, Gulf of Mexico, and Indonesia

Four principal depositional elements are recognized in deep-water depositional environments offshore Nigeria, Gulf of Mexico, and Indonesia. These include channels, levees, frontal splays, and debris flow deposits. Individual channels range from moderate to high sinuosity and are up to 2-3 km wide. Channel fills can be single-stage or multi-stage fill. In the latter channel type, leveed channel complexes are said to exist. In many instances, channel meander evolution is characterized by aggradation and down-system meander loop migration. The result of this process is a reservoir-prone fairway many times the width of the single channel. Levees are constructed by flow stripping of the upper part of the turbidity flow. Rapid sedimentation just outboard of the levee crest occurs in response to the rapid flow deceleration that accompanies this process. Sediment waves commonly characterize proximal levee environments.

Frontal splays commonly form at the mouths of leveed channels. This depositional element commonly is characterized by channelization nearly to its most distal extremities. The channel patterns observed range from distributary to braided. Channels atop the frontal splays are narrower and display significantly less relief than updip isolated leveed channels. Relief from levee crest to channel floor commonly is less than 2-4 meters.

Debris flow deposits range from channelized to sheet or lobe morphology. The distinguishing aspect of debris flow deposits is the linear scouring and grooving that characterizes the erosional surface of the subjacent surface. These grooves can be up to 0.75 km wide, 30 m deep and kilometers in length and in map view, are divergent down-system.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado