Evidence of episodic coastal change during the Late Holocene: The Dungeness barrier complex, SE England

The sediments of the Dungeness gravel foreland and, in particular, the back-barrier marshland of Romney Marsh are studied in an investigation of (i) temporal and spatial changes in the relative importance of factors driving drift-aligned barrier evolution and (ii) non-linear coastal change. Evidence from palaeomagnetic secular variation (PSV) dating of six marshland cores coupled with particle size data and statistical analysis of heterolithic tidal rhythmites reveals a phase of rapid tidal sedimentation in both inter- and back-barrier ‘lows’ during the period of c. 1100 to 500 years ago, driven primarily by changing coastal morphology, accommodation space and tidal dynamics. Variations in particle size and layer thickness can be related directly to tidal cyclicity, from which accretion rates of the order of 0.3 m/year are determined. Once shoreface emergence occurred, it is apparent that gravel barrier and marshland deposition were both episodic and rapid. Within this non-linear response, two periods of episodic marshland accretion are identified: an earlier one 1100–600 years ago resulting from cannibalisation of the southern shore of Dungeness foreland and inundation of the exposed inter-ridge lows, and a later period about 600–500 years ago in a true back-barrier setting created by eastward extension of the shoreface spit and foreland ness. A high level of inter-dependence between shoreface, barrier and back- (and inter-) barrier environments is confirmed, as well as marked non-linearity directly related to this inter-dependence. Here, drift-aligned gravel foreland evolution takes place through lateral (down-drift) rollover controlled by shoreface topography and continued sediment supply through cannibalisation (sediment recycling).