INTERNAL STRUCTURE OF WAVE-FORMED RIPPLE MARKS IN THE NEARSHORE ZONE

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SUMMARY

Wave-formed ripple marks in the nearshore zones of the Baltic Sea (tideless) and North Sea (tidal) exhibit a unidirectional internal lamination identical to that of current ripples. This holds true whether the ripples are symmetrical or asymmetrical. In most cases wave-formed ripple laminae dip toward shore and can thereby provide a shoreline direction indicator when found in ancient sediments. The sediment transport direction, however, may be other than in the foreset laminae dip direction, and cross-lamination as a sediment transport direction indicator should be used with caution.

Ripple height, wave length and the orientation of the ripple internal structure are dependent upon both the orbital diameter and the velocity of the positive component of oscillation of the waves forming them. The thickness of the individual laminae making up ripples is highly dependent upon sediment grain size; the role hydrodynamics plays is problematic.

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