Submarine sedimentation on a developing Holocene fan delta

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Abstract
The submarine morphology, sediments, and three‐dimensional geometry of a developing fan delta are described using data from acoustic surveys, bottom sampling, and observations from a manned submersible. The fan system is being built in a British Columbian fjord (water depth 410 m) supplied with coarse‐grained sediments from a fjord‐side river.Construction of the subaqueous fan began about 10–12,000 yr BP and is ongoing. The system is analogous to part of one fault‐uplift sedimentation cycle in ancient fan deltas. Initially, when offshore relief was at a maximum, acoustically chaotic sediment wedges were emplaced over fjord‐bottom glaciomarine deposits. Subsequent aggradation/progradation resulted in moderately dipping sequences interrupted by local chaotic units. The present fan surface (average slope 13°) is divided into six zones arranged concentrically from the fan apex, on the basis of form, sediment and process interpretations. Continued subaqueous fan growth results from settling of river‐derived sediments from suspension and downslope sediment dispersal by episodic gravity flows, apparently fed by underflows from the river.