The Character and Genesis of Mass Transport Complexes II: Processes, Classification and Insights from Outcrops

Ole Martinsen¹ and Henry W. Posamentier^2
1 Norsk Hydro Research Centre, Bergen, Norway
² Anadarko Canada Corporation, Calgary, AB

Sediment instability and resulting down slope sediment movement that produces mass transport complexes are inherent processes on all subaqueous slopes and vary tremendously in scale from cubic meters to several thousand cubic kilometers. Critical aspects of such complexes include timing of formation, occurrence, geometry and process since they must be differentiated from, but can help predict reservoir-bearing units. Mass transport complexes encompass a continuous spectrum of subaqueous slope processes that grade into one another. The processes include creep, sliding, slumping, debris flow and fall of material and are controlled by other mechanisms than fluid turbulence. A wide range of deposits can be produced that signify local and regional depositional controls such as sedimentation rate, slope angle, slope accommodation and tectonic influence. A detailed understanding of these processes is a requirement for spatial and temporal understanding of deep-water stratigraphy and for ground-truthing seismic interpretation.

Recent slope settings and 3D seismic surveys provide insight into the geomorphology and timing of such sediment movement but do not provide a detailed insight into the deposits. This insight is important to establish relationships between type of mass transport complex and overall depositional setting. Detailed outcrop studies provide essential understanding of the range of processes and relationship to settings within which sediment instability can occur. The Upper Carboniferous deep-water deposits of the Shannon Basin, western Ireland show unparalleled examples of mass transport complexes that can be related to the spatial and temporal depositional setting. Other outcrop examples will also be shown.