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The Sedimentology of Milk - Studying Deposition and Transport Modes of Moving Clay Suspensions

 

Schieber, Juergen1, John B. Southard2, Kevin G. Thaisen1 (1) Indiana University, Bloomington, IN (2) MIT, Cambridge, MA

 

Notwithstanding the observation of nearshore accretion of mudbanks in Surniame, it is a widespread belief that muds mainly accumulate in quiet environments that only see intermittent and weak current activity. To better understand the controls on mud deposition from moving suspensions, we have conducted flume studies in a racetrack flume with water circulation by paddle belt. This avoids destruction of clay floccules and results in more “natural” behavior of clay suspensions.

 

Our experiments have shown that floccule formation is a common phenomenon, and that at flow velocities between 20-30 cm/sec, migrating floccule patches form that appear to be the equivalent of ripples in coarser sediments. These ripples are difficult to observe because above 50 mg/l suspended sediment the fluid becomes impenetrable to direct observation.

 

Observing through the flume bottom with strong backlighting allows visualization of ripple migration and accretion at suspended sediment concentrations of up to 2000 mg/l. Addition of tracer spikes (hematite powder) allows visualization of the evolving bed geometry upon dissection of the sediment.

 

At flow velocities where sand would move across the flume bottom in bedload, mud as well moves in bedload in the form of floc ripples. With further clay addition and/or lowering of flow velocity, floc ripples may become stationary, spread out, and coalesce to form a contiguous mud bed. Further sediment addition causes floc ripples to migrate over this initial bed, allows their basal portions to adhere to previously deposited muds, and in this way vertical accretion of a mud bed is achieved.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California