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Can a Single Turbidite Flow Decouple and Become Separate High and Low Concentration Flows?

McHargue, Tim *1
(1) Geological and Environmental Sciences, Stanford University, Stanford, CA.

The cross-sectional profile of some turbidite channel systems displays a small, sinuous channel element within a much larger container with low sinuosity. The sinuous channel element typically is 100-300m wide and 10-30m deep with a cross-sectional area of 1 to 9 KmSq, whereas the container, often confined by outer levees, is kilometers wide and hundreds of meters deep with a cross-sectional area that is 2 to 3 orders of magnitude larger than the area of the channel element. Well logs and 3D seismic data from numerous channel systems confirm that turbidite sands typically are concentrated within the element-scale channel unless the confinement relief is thin, on the order of 10m or less. Therefore, collectively, architecture and sediment distribution imply that the turbidity currents traveling through these channel systems were stratified, and the higher concentration portion of these flows were restricted to the element-scale channels. The dilute upper portion of these flows filled and overspilled a container that was several times wider and multiple orders of magnitude larger than the underlying channel element. Furthermore, the upper, dilute layer followed a low-sinuosity path and was in contact with the container floor, rather than the underlying high concentration layer, for 60% to 90% of its width.

Because the two layers of the turbidity flow have different concentrations, markedly different volumes, pathways with different sinuosities and limited vertical contact, it is reasonable to consider that the two layers may have traveled at different velocities and decoupled. The high concentration portion of the flow could have traveled at a higher velocity, albeit along a path of higher sinuosity, than the dilute portion of the flow. If decoupled, what are the flow parameters of the high density flow that allow it to sustain suspension of coarse grains across long distances?


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California