Stratigraphy and Geomorphology of Deep-Water Mass Transport Complexes Based on 3D Seismic Data

Abstract

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. Greater thicknesses are observed where successive flows are amalgamated. This report documents both the internal architectural/stratigraphic as well as the external geomorphic attributes of such deposits as imaged by 3D seismic data. Mass transport deposits can be recognized seismically by certain geomorphologic as well as stratigraphic distinguishing characteristics:surfaces underlying such deposits commonly are characterized by extensive scour, commonly taking the form of extensive linear grooves as much as 20 km long, 750 m wide, and 40 m deep, 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 sea floor.The upper bounding surface commonly is characterized by irregular to hummocky relief and can be bounded laterally by steep to gentle flanks.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 obscure and difficult to recognize.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. Introduction Mass transport deposits are a common feature in many deep-water settings and have been well described in the literature (Sangree and Widmire, 1977; Prior and Coleman, 1984; Prior et al., 1984; Kenyon, 1987; Weimer, 1991; Masson et al., 1993; Mulder and Cochonat, 1996; Piper et al., 1997; Gee et al., 1999, 2001; Posamentier and Kolla, 2003). In some instances such deposits can comprise up to fifty percent of the stratigraphic section. They can be observed both in slope as well as basin floor settings, in some instances as far as hundreds of kilometers across the basin floor. Through the use of imaging by 3D seismic data, the internal as well as external character of such deposits can be studied. Shallow-buried deposits can be resolved seismically down to a few meters and reveal a wealth of detail. The provenance of such deposits at the mid to upper continental slope as well as more local flanks of steep deep-water physiographic features, also can be imaged. This paper describes both the internal and external morphology of a range of deep-water mass transport complexes. Such deposits can occur in a broad range of shapes and sizes, with a broad range of internal geometries from massive to crudely bedded. They can be deposited from the continental slope to the basin floor. They can also be quite local in nature, such as those that form on the flanks of salt domes or mud volcanoes, or on the inner and outer flanks of turbidity-flow channel levees.