3-D Seismic Interpretation of Mass-Transport Complexes: Examples from the Offshore Nile Delta and West Africa

Dorthe Moeller Hansen¹, Jonathan Redfern¹, Rob Gawthorpe¹, Gianluca Badalini², and Martin Gee^1
1 University of Manchester, Manchester, United Kingdom
² BG Group, Rio de Janeiro, Brazil
³ Universiti Brunei Darussalam, Tungku Link, Brunei

Mass-transport complexes (MTCs) are major features of submarine slopes and play a key role in down-slope sediment transport on continental margins. MTCs have traditionally been studied using marine geophysical techniques such as sidescan sonar and multibeam systems and through terrestrial outcrop studies, all of which are limited by their inherent lack of good three-dimensional and scale capabilities. MTCs are exceptionally well imaged on 3D seismic data and three-dimensional imaging allows for their external and internal character, as well as structural and stratigraphic context to be resolved in great detail.

Drawing upon subsurface examples from 3D seismic datasets from the offshore Nile Delta and Angola we describe the detailed morphology and internal heterogeneity of large-scale mass-transport complexes. In addition, we discuss the stratigraphic and structural context of the MTCs. These MTCs cover areas of several hundred km2, have run-out distances >50 km and comprise volumes >10km3. The basal shear surfaces are often characterised by erosional scoures and the upper bounding surfaces commonly exhibit an irregular to hummocky relief. The internal seismic character of, and within, individual MTCs varies from blocky through chaotic to transparent, reflecting different processes of mass-transport. The location of the MTCs is partly controlled by the presence of underlying MTCs and channel-levee systems and, conversely, the MTCs are seen to exert a control upon the deposition of subsequent units.