RUNOUT AND FINE-SEDIMENT DEPOSITS OF AXISYMMETRICAL TURBIDITY CURRENTS

We develop a model that describes the runout behavior and resulting de posit of a radially spreading, suspension-driven gravity current on a surface of negligible slope. Our analysis considers the separate cases of constant-volume and constant-flux sources. It incorporates express ions for the conservation of volume, a Froude number condition at the current front, and the evolution of the driving suspension due to sett ling of particles to the underlying bed. The mode! captures the key fe atures of a range of experimental observations. The analysis also prov ides important scaling relationships between the geometry of a deposit and the source conditions for the deposit-forming flow, as well as ex plicit expressions for flow speed and deposit thickness as functions o f radial distance from the source. Among the results of our study we f ind that, in the absence of information regarding flow history, the ge ometries of relatively well-sorted deposits generated by flows with so urce conditions of constant volume or constant flux are virtually indi stinguishable. The results of our analysis can be used by geologists i n the interpretation of some geologically important gravity-surge depo sits. Using our analytical results, we consider three previously studi ed, radially symmetric turbidites of the Hispaniola-Caicos basin in th e western Atlantic Ocean, From gross geometry and grain size of the tu rbidites alone we estimate for the respective deposit-forming events t hat upon entry into the basin the initial sediment concentrations were approximately 3% by volume and the total volumes were roughly between 30 km(3) and 100 km(3) Each of the suspension-driven flows is inferre d to have spread into the basin with a characteristic speed of 3-5 m s (-1), and reached its ultimate runout length of about 60-75 km while l aying down a deposit over a period of about 10-12 hours.