Abstract:
Comparison of architectural elements between modern turbidite systems can improve our understanding of the reservoir properties of sandy intervals in submarine fans and of their lateral continuity and vertical connectivity. Like elements from different systems can be compared, however, only if differences in their geometry and physical scales, duration of active growth, and depositional processes are considered. Recent data from high-resolution, seismic-reflection surveys and ODP wells allow a new synthesis of the architecture of sandy submarine fans, based principally on Amazon and Hueneme fans. For both systems, turbidite sedimentation is turned on and off by sea-level changes and, for each fan, one initiation process for turbidity currents tends to dominate. Amazon Fan, which is fed by Pleistocene delta slumps, and the small sandy Hueneme fan which is fed by hyperpycnal flow, represent two simple, but extreme, end members of sandy fans. Small fans, such as Hueneme fan, show complex architectural geometry because changes in sea level can modify or augment the dominant initiation process, possibly precluding a simple predictability through time. Hyperpycnal flow, load-induced slumping, seismically-induced slumping, and canyon-head flushing all play a role in turbidity current initiation at different times during sea-level change for small, basin-margin fans. Channel aggradation characterizes Hueneme fan with little progradation into the basin. In contrast, the much larger Amazon fan shows rapid channel progradation that produces commonly repeated, but relatively short-lived, architectural geometries resulting from autocyclic changes including meander cut-offs and avulsions.