The Character and Genesis of Mass Transport Complexes I: Geomorphology and Process Sedimentology from 3-D Seismic Data

Henry Posamentier¹ and Ole Martinsen^2
1 Anadarko Canada Corporation, Calgary, AB
² Norsk Hydro Research Centre, Bergen, Norway

Extensive deep-water mass transport deposits are observed both in slope as well as basin settings. These deposits can occur as sheets, lobes, and channel fills, and can reach 150 m or more in thickness. Mass transport deposits are associated with certain geomorphologic as well as stratigraphic distinguishing characteristics: 1) surfaces underlying such deposits commonly are characterized by extensive scour, commonly taking the form of extensive linear grooves that tend to diverge down-system. These grooves are inferred to be formed by the passage of blocks imbedded at the base of the flow mass that are dragged across the underlying substrate. 2) The upper bounding surface commonly is characterized by irregular to hummocky relief and can be bounded laterally by steep to gentle flanks. 3) In section view, mass transport deposits are characterized by transparent to chaotic seismic reflections. Mass transport units commonly amalgamate, although surfaces between successive mass transport deposits can be difficult to recognize. 4) The morphology of mass transport deposits can be channel or lobe form. Mass transport channels are relatively straight and commonly floored by a grooved base. In some instances mass transport lobes are characterized by extensive low-angle thrust faults associated with compression, commonly at their termini.

Two distinct types of mass transport deposit can be recognized: 1) those that glide along a relatively smooth decollement surface, and 2) those that erosively traverse the sea floor leaving the basal surface heavily grooved and scoured. Each of these two processes likely is associated with a distinctive flow rheology, the former tending to be more coherent and commonly made up of discrete blocks, whereas the latter less coherent and commonly more disrupted and devoid of fabric.