Tidal cycles preserved in late Holocene tidal rhythmites, the Wainway Channel, Romney Marsh, southeast England

Intercalated layers of sand and mud deposited in tide-dominated environments, usually of extreme tidal range, have been shown to exhibit sinusoidal variations in thickness, particularly of the sand layers. Tidal cyclicities derived from statistical analysis of these tidal rhythmites have been reported from several ancient and modern environments. Less attention has been paid to intertidal deposits which accumulated under a more moderate tidal range. This paper reports evidence of tidal cycles in a late Holocene laminated sequence infilling the former Wainway Channel on Walland Marsh which forms part of the Romney Marsh depositional complex on the southeast coast of England. The Wainway was a blind tidal channel which drained westwards into the estuary of the River Rother in Rye Bay where the current tidal range is around 6.7 m. The channel, and adjoining intertidal flats and salt marshes, were reclaimed in a piecemeal fashion through the 17th century in the study area. Autocorrelation and spectral analysis of variations in sand layer thickness up core reveals periodicities of 2, 5 to 8 and 11 to 13 layers/cycle which were interpreted as evidence of a diurnal inequality, neap–spring and lunar monthly cyclicity, respectively, within these sediments. Very short-term (several months) deposition rates inferred from the statistical analysis were equivalent to 1 m/yr. However, evidence of annual cycles preserved within these deposits indicate that the sedimentary record was not continuous, and that actual accumulation rates were approximately 0.5 m/yr on average over the longer term (several years).