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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Research
Vol. 82 (2012), No. 7. (July), Pages 464-468
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Modeling the Rollovers of Sandy Clinoforms from the Gravity Effect on Previous HitWaveNext Hit-Agitated Sand

Neil C. Mitchell

Abstract

Clinoforms on coasts exposed to ocean waves form from sand exported from the shoreface during extreme Previous HitwaveNext Hit conditions and deposited where Previous HitwaveNext Hit action diminishes. Elsewhere, it is shown that during upper 5-percentile Previous HitwaveNext Hit conditions, Previous HitwaveNext Hit-induced shear stresses exceed the sediment threshold of motion to below the clinoform rollovers. Experiments and theory suggest that, where bed sediments are agitated by waves, the effect of gravity should move particles down-slope with a flux proportional to the slope. Combined with considerations of continuity, this implies a diffusion of the sediment topography, a property that would explain the smooth seabed morphology found at sandy rollovers where recorded with multibeam sonar. For situations where this gravity effect dominates, a simple analytical expression developed here shows how the rollover curvature should relate to Previous HitwaveNext Hit properties and to the offshore component of sediment flux. More sharply curved rollovers are expected where waves have short periods or where the sediment flux is large. Relative sediment fluxes were calculated using the model from rollover curvature and Previous HitwaveNext Hit properties for sites from California, southeast Australia, and Atlantic and Mediterranean Iberia. The relative magnitudes of the fluxes are roughly as would be expected from local physiography and coastal erosion rates. For sandy clinoforms developed under mainly Previous HitwaveNext Hit influences, the model could be useful for exploring variations within clinoform datasets (e.g., how varied convexity in an area of uniform Previous HitwaveNext Hit properties reflects varied sediment flux) and for interpreting how varied curvatures of rollovers within seismic stratigraphy reflect how Previous HitwaveTop climate and flux have varied in the past.


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