Abstract

Unidirectional, oscillatory and combined-flow paleocurrent data from many ancient wave-dominated coastlines indicate that sediment transport was directed offshore at angles of 70 to 90 degrees from the inferred local paleoshoreline. Solemarks and parting lineations from turbidite-like storm beds and solemarks from hummocky beds indicate that flows transporting sediment offshore were orthogonal to the local shoreline. The shore-normal orientations of solemarks, parting lineation and asymmetric ripples on hummocky cross-stratification and their orthogonal relationship with respect to wave-ripple crest orientation indicate that the dominant direction of wave approach at the sediment-water interface was also orthogonal to the shoreline. The formation of hummocky cross-stratification by an along-shore flow component superimposed on oscillatory wave motion is not supported by paleocurrent data. Rather, much of the evidence from the ancient record suggests that hummocky cross-stratification forms under high-energy, oscillatory-flow with a weak, shore-normal, combined-flow component. The orientation of wave-ripple crests from the lower shoreface to offshore-transitional zone of wave-dominated coasts can be used to approximate the local paleoshoreline trend. The paleocurrent data from the ancient examples suggest a strong predominance of offshore-directed sediment transport, as opposed to the nearly shore-parallel orientation of currents observed in modern geostrophic flows.

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