BASIN-FLOOR FAN ARCHITECTURE: SIGNALS OF SEA LEVEL BEHAVIOUR (Invited Presentation)

The conventional lowstand model for dispersing sediment across the sedimentary shelf and to the deepwater basin floor relies on forced regressive shorelines on the shelf and subsequent lowstand sand delivery to the basin floor in a series of ordered phases (early and late lowstand). This model works well and does not necessarily require a large feeder river, because it is accommodation driven. However, the model is problematic for Greenhouse times when sea-level amplitudes and frequency were modest, and has difficulty to explain large and ubiquitous Greenhouse fans. During the last decade, examples of slope sediment delivery and basin-floor fan growth during rising and highstand of sea level have become commonplace. The question of recognizing the signals of highstand delivery of deepwater sands, and the distinction from lowstand delivery has therefore become important. A series of criteria are suggested, and these include architectural and other signals resultant from the highstand sediment flux being necessarily large and the likelihood that coeval shelf edges were preferentially storm-wave dominated. Despite the importance of wave-domination to accumulate and strike-feed sand along the shelf edges in this model, a river dominated process regime at specific exit points along the shelf is also necessary, unless the shelf-edge sandbelts are captured by canyons.