Effects of Gradual Increment of Clay Concentration on Turbidity Flow Structure

Ramirez, Johana M.¹; Eggenhuisen, Joris; and Cartigny, Matthieu
¹[email protected]

The fluid-dynamic characteristics of a flow can be transformed by increasing the concentration of fine silts and clay. Here, analogue Froude-scaled flume experiments at the Eutotank Laboratories are used to examine the effect of clay in turbidity currents. The generic concepts from these experiments are that the addition of small amounts of clay increase the transport efficiency of the flow causing the sand particles to be transported far away from the inlet source. Moreover, the fluid dynamics of turbidity currents do not resemble the ones described by Baas et al. (2002, 2008 & 2009) for open-channel flows in which five flow types are recognized 1.Turbulent flow (normally turbulent) 2. Turbulence-enhanced transitional flow (strongly turbulent) 3. Lower transitional plug flow (strong turbulence at the bottom and lower turbulence at the top) 4. Upper transitional plug flow (damped turbulence caused by gelling of the clay) 5. Quasi-laminar plug flow (turbulence is suppressed/gelling dominates). Turbidity currents lack this complex five-step transition from turbulent to laminar flow as the clay content increases. The effect of clay in turbidity flow structure has a major implications for tubiditic sand-body development. If the turbidity system transports sand together with clay particles, the sand is deposited far into the basin (In the laboratory the thickest packages occur at low slopes of 3 degrees). On the contrary, if the flow is free-clay laden, thick sand bodies can also be found close to the source, in the laboratory at slopes of 7-9 degrees. The observations are in close correspondence with the concepts derived from analogue modeling and imply that the characterization of original flow composition allows for a better understanding of sand distribution and basin infill.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013