Investigating the Existence of Anabranching Channels in Submarine Slope Turbidite Systems; Can They Exist

Lorna J. Strachan¹ and Rob L. Gawthorpe^2
1SGGES, Geology, University of Auckland, Auckland, New Zealand
²SEAES, University of Manchester, Manchester, United Kingdom

Submarine channel complexes are characterised by the presence of multiple cross-cutting thalweg traces and adjacent levees, which display a range of vertical and lateral stacking patterns. Evolution of these systems varies in space and time, but typically is explained through the formation of a single channel via incision or levee aggradation, channel filling and abandonment.

This model works well for many examples, yet by following its principal tenet, the existence of anabranching channels (i.e. multiple, coexisting channel systems) is impossible. Several examples from the modern day sea floor, however, reveal braided anabranching planforms. This suggests that, locally, it is possible to form and maintain coexisting multiple channel segments.

The aim of this poster is to use a 3D subsurface seismic dataset from offshore Angola to investigate the existence of multiple coexisting anabranch channels, in an ancient submarine channel complex.

Iso-proportional slice attribute maps taken through the channel complex reveal an evolving system characterized by multiple sinuous anabranch segments formed during early phases of formation. The channels are interpreted to have formed simultaneously in a low-gradient, avulsion-dominated system. Later phase channel planforms are characterized by a single sinuous channel.

These observations suggest that: 1. anabranch multiple channel forms are possible within submarine turbidite systems, 2. they are probably related to disqequilibrium adjustments of the channel slope early within evolution of the complex, and 3. the system may evolve from anabranching to a single channel trace with time.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas