--> Experimental Study from the Effect of Large-Scale Relay Ramps as Pathway for Turbidity Currents, Athmer, Wiebke; Groenenberg, Remco M.; Luthi, Stefan M., #90100 (2009)

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Experimental Study from the Effect of Large-Scale Relay Ramps as Pathway for Turbidity Currents

Athmer, Wiebke1
 Groenenberg, Remco M.1
 Luthi, Stefan M.1

1Department of Geotechnology, Delft University of Technology, Delft, Netherlands.

Large-scale relay ramps with dimensions in the kilometer range are found to influence the sedimentary pathways in fluvial and deltaic settings of rifting systems such as the East African Rift and the Suez Rift, but their impact on sediment dispersal in deep-marine settings and particularly turbidity currents is less clear. Understanding the influence of syn-sedimentary faulting on turbidite deposition is, however, of great relevance to better locate reservoir sands and to improve predictive depositional models at passive continental margin.

A novel approach was used that combines analog experiments with numerical flow simulations to analyze the effect of relay ramps on turbidite flow and deposition. The analog experiments were performed in a laboratory sandbox using a brittle-ductile setup with sand and silicone, underlain by a plastic sheet which is steadily pulled during the experiment to produce an oblique rift setting with relay ramps of various geometries. As soon as a relay ramp developed, the laboratory experiment was stopped and the topography photographed and digitally scanned with a 3D-video laser. The scan was then transformed into a digital elevation model and subsequently upscaled to receive relay ramps at a scale comparable to a rift. Afterwards it was used as initial topography in a computer program in which turbidity currents were numerically simulated under an oblique inflow direction to the relay ramp, both with and without flow constraints. The flow parameters were approximated to an assumed average of natural flows.

The role of relay ramps as pathways for turbidity currents was found to be strongly dependent on its geometry. All experimental relay ramps had a basinward tilt which is known to be very common in natural settings too. Without a flow constraint most sediment was shed over the hanging wall fault of these relay ramps directly into the basin. With a channel as flow constraint more sediment flowed down the ramp axis, but channel spillover and basinward ramp tilt redirected most of the sediment flow down the fault slope into the basin. Only with a landward-oriented tilt of the relay ramp, which was manually applied, did significant sedimentation take place on the ramp. However, a large amount of the flow is still shed above the inner normal fault into the basin, thus forming a second depocenter. Landward tilted relay ramps, however, are relatively rare in natural settings but usually of very large scale.


AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil