Morphology and architecture of confined-to-unconfined flow transitions in modern and ancient deep-marine systems.

Confined-to-unconfined flow transitions in deep-marine systems occur in areas where either a submarine channel passes into a depositional sheet/lobe or a submarine canyon passes into a submarine channel or basin plain. Transition zones are areas of complex interplay between erosive and depositional processes. Much recent research has concentrated on submarine channels or depositional lobes. This thesis attempts to identify characteristic features and deposits associated with zones of confined-to-unconfined flow transition. GLORIA sidescan data from the Bering Sea is studied here in detail to investigate the role of basin configuration in relation to the development of different styles of transition zone within a modern deep-sea environment. A high-resolution study of the channel-mouth of the Petit Rhone Channel in the NW Mediterranean reveals that channel-mouth areas are candidates for an hydraulic jump to occur (Komar 1971). Breaks-in-slope (up to 3) occur in the mouth of the Petit Rhone Channel and have produced a characteristic channel- mouth erosion facies associated with increased flow turbulence. This study used ancient analogues from the Eocene Hecho Supergroup (Mutti et al. 1989) to make detailed investigations into facies and facies associations in areas of inferred transition from channel-to-lobe and from canyons-to-slope. All but one of the turbidite systems of the Hecho Supergroup exhibit submarine channel development The Arro Sandbody does not exhibit features characteristic of a submarine channel deposit. A detailed study of this system illustrates the importance of structural control on turbidite fan development. Uplift in the shelf region associated with the Arro Sandbody may have produced a break-in-slope in the canyon area which allowed flows to become highly turbulent due to hydraulic jump conditions. Other turbidite systems of the Hecho Supergroup exhibit vertical facies variation from a highly erosive facies at the base of the sections to a more depositional facies higher in the sequences. This temporal facies variation can be attributed to slope degradation processes active contemporaneous with sedimentation acting to reduce slope angle and breaks-in-slope. This inferred change in topographic conditions is thought to have direct relevance to transition zone processes. In conclusion, conceptual frameworks for transition zones have been developed, both for modern deep-marine systems and ancient deep-marine systems. The data collected in this study indicates that young fan systems with irregular sea-floor topography, are more likely to develop erosive facies and faces associations in transition zone areas as the irregular topography can cause turbidity flows to hydraulically jump. More mature systems tend to have a smooth sea-floor topography, and this produces more gradual transition zone facies as flows tend not to hydraulically jump.