High-Latitude Recipe for Sand Delivery to the Deepwater Via Hyperpycnal Flow: A Greenhouse Example from the Early Eocene, Central Spitsbergen Basin

Andrew L. Petter and Ronald J. Steel
University of Texas at Austin, Austin, TX

Two basic requirements exist for generation of turbidity currents directly from fluvial discharge (i.e., hyperpycnal flow). Firstly, sediment concentration at the river mouth must be sufficient to cause fluvial discharge to be denser than ambient basin water. Sediment concentration at the river mouth is controlled by the upstream influences of the fluvial drainage basin. For efficient production of hyperpycnal flow, annual sediment budgets should be concentrated within short time spans, such as during large-magnitude floods, rather than spread throughout the year. Drainage basins with monsoonal climates are ideal for creating large-magnitude floods with high sediment loads because intense precipitation alternates with dry seasons, reducing vegetative groundcover that would preclude soil erosion in humid climates. Small, steep basins with high-density drainages also promote runoff of precipitation over groundwater infiltration, and thus, hinterland erosion.

The second requirement is the presence of a slope break directly basinwards of the river mouth. Delta-front slope breaks on the shelf give way to decreased offshore gradients, causing hyperpycnal flow to decelerate and deposit before reaching deepwater. However, deltas sited at the shelf edge allow the delta-front slope to superimpose on the long run-out and high gradient of the shelf-margin clinoform. Consequently, hyperpycnal flow emerging from shelf-edge deltas will accelerate downslope and have the potential to ignite and bypass to the basin floor. Therefore, the probability of hyperpycnite deposition in deepwater is increased when drainage basins with the proper topographic and climatic conditions discharge at the shelf margin, as evidenced by early Eocene shelf margins on Spitsbergen.