Shelf Edge Trajectory Styles and the Optimal Timing for Sediment Accumulation on the Continental Shelf, and Transport to the Deep Marine: Concepts and Exceptions to the Rule

Sverre Henriksen¹, William Helland-Hansen², Scott Bullimore^2,3, Kristian Helle², and Britta Paasch^1
1Statoil Research Center, Rotvoll, N-7005 Trondheim, Norway, E-mail: [email protected]
²University of Bergen, Department of Earth Science, Allegt. 41, N-5007, Bergen, Norway
³Statoil ASA, Sandslihaugen 30, N-5020 Bergen, Norway

A fall in relative sea level will generally result in a seaward shift in the locus of sedimentation. If relative sea level fall are sufficiently large, a high angle negative (descending) shelf edge trajectory will result. During this stage, the shelf and upper slope may be deeply incised and allow bypass of substantial amounts of sediments to the deep marine through submarine canyons. In this situation fluvial systems may reach the outer shelf and provide an efficient feeder system allowing periods of continuous flow to the deep marine. This is reflected in the 3D seismic geo-morphology with development of high sinuosity turbidite channels.

Highstand in relative sea level will generally result in stacking of shallow marine and fluvial sediments on the continental shelf. If sedimentation rates are sufficiently high, the shelf edge will build vertical and basinward, giving a positive (ascending) shelf edge trajectory. During this stage there will generally be little transport of sediments to the deep marine. However, as exemplified by this study, there are a number of cases where the sedimentation rates totally outpace the accommodation room created by the highstand situation. In such cases the shelf edge may be over steepened and eventually collapse. This will result in dislocation of sediments to the deep marine. But the lack of an efficient feeder system will at the shelf edge will generally give smaller deep marine fans than those produced during lowstand of sea level. These fans appear to be built up by more event based turbidites, without the massive channelization seen in the canyon fed systems.

Finally, if a long-lived, large canyon incises the shelf and link up to an efficient feeder system, transport of sediment to the deep marine may prevail during both lowstand and highstand. In this case there is a good possibility for events of continuous flow for long periods of time and over several cycles of relative sea level change.

AAPG Search and Discovery Article #90079©2008 AAPG Hedberg Conference, Ushuaia-Patagonia, Argentina