AV俱乐部

B. Sc. Honours, Earth Sciences, AV俱乐部, 2003

Increased interest in deep-water sedimentation processes over the past two decades has revealed the ubiquity of submarine slope mass failures on continental margins. Slope failure appears to be a particularly critical process in the development of large deep-water sedimentary fans. A 7,000 km² 3D and a regional 2D seismic grid of hydrocarbon seismic reflection exploration data are used to construct a Quaternary stratigraphy and assess controls on sedimentation processes for the central and western deep-water Nile fan, offshore Egypt. These results will help understand the role of mass failure processes in the Quaternary construction of the Nile fan.

The deep-water Nile fan is a high sedimentation rate environment in an active seismogenic zone. The Quaternary section, locally up to a kilometre thick, is dominated by submarine channel systems and mass transport deposits. Regional mapping within the central and western Nile Fan reveals the presence of seven large mass transport complexes (MTCs) within this section, each comprising greater than 100 km³ of sediment. These large MTCs are used to separate the Quaternary Nile fan into seven stratigraphic units.

Six of the MTCs were apparently deposited as large cohesive slides, each comprising up to 2,000 km³ of sediment. These MTCs are interpreted to contain large cohesive blocks (generally up to 500 m by 300 m and up to 75 m thick), sometimes showing either compressional or extensional structures, as well as basal shear structures. These six MTCs are each overlain by extensive submarine channel systems that are connected updip to headwall-scar confined submarine canyons. These MTCs may have formed in response to high sedimentation rates and seismic ground shaking. The seventh large MTC comprises as a series of interpreted debris flows originating near two large gas chimneys and a normal fault located on the upper slope.

These data show a link between large slope failure events and the development of submarine canyons and channel systems. These particular large slope failures initiate on the upper slope creating extensive regions of sediment evacuation, extensive headwall scarps, and are accompanied by thick accumulations of MTCs on the mid-slope. Submarine canyons appear to establish on the upper slope within headwall scarps immediately following a major slope failure event. These canyons then serve as the principal conduits for sediment transport to deepwater, probably as turbidity current. By this mechanism, large slope failures may mark major shifts in deepwater turbidite depocenters that can be traced on regional seismic data. This model of fan development is important to explorationists in searching for turbidite-hosted hydrocarbon plays.

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Supervisors: David Mosher / Grant Wach