Coupling Flow and Deposit Properties of Partly Cohesive High-Density Turbidity Currents: From Experimental Approach

Rafael Manica¹, Jaco H. Baas², Jeff Peakall³, Rogerio D. Maestri¹, and Ana Luiza O. Borges^1
1NECOD/IPH/UFRGS, Porto Alegre, Brazil
²University of Wales Bangor, Bangor, United Kingdom
³University of Leeds, Leeds, United Kingdom

A series of detailed laboratory experiments were performed to examine the influence of cohesive clay on the behaviour of high-density turbidity currents and their deposits. The flows carried a mixture of non-cohesive (silt-sized glass beads) and cohesive sediment (kaolin) at a total volumetric concentration of 20%, Relative clay concentrations were 0%, 10%, 25%, 50%, 75%, 90% and 100%. Video-Images analysis with the aid of an interactive white board was used to determine dynamic geometrical properties of the flow, such flow thickness, mixing processes, and density stratification. High-frequency time-series of suspended sediment concentration and flow velocity were collected using Ultra High Concentration Meters and Ultrasonic Doppler Velocity Probes. The rheological properties of the flows were also evaluated. Deposit samples were analysed using Scanning Electron Microscopy (SEM) in order to study depositional textures. Although most flows had similar geometrical properties, their velocity and concentration structure varied greatly and were strongly coupled to relative clay content through changes in rheology. In weakly cohesive flows, a high-concentrating basal layer developed from rapid settling of silt, whereas in strongly cohesive, clay-rich flows a basal mobile fluid mud layer was inferred from the velocity and concentration data. These flow properties were coupled to deposit properties (such as vertical gradients in grain size and clay content) and three distinct depositional processes were defined (high-density turbidity current, debris flow, and a transitional flow type). The implications of the experimental results for natural turbidites are discussed.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas