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Holocene relative sea-level (RSL) change is investigated at Nyland Hill (Somerset Levels). The lithostratigraphy comprises turfa peat underlying marine clay, both onlapping a sloping Upper Palaeozoic basement. The altitude of the peat-clay contact ranges from 2.42 to 4.52 m OD, becoming lower down basement slope, yet 14C dates of three samples taken laterally along the contact at different altitudes yield similar ages (3640-3330, 3715-3460, 3725-3465 cal. yrs BP), suggesting either very rapid (‘instantaneous’) RSL rise or sediment compaction. Biostratigraphic data indicate a gradual transition to marine conditions across the peat-clay contact. Therefore, the height difference is interpreted as evidence for significant compaction. We consider 4.64 m OD the minimum pre-compaction altitude, indicating maximum observed compaction of 2.22 m. The clay surface, reclaimed during Roman occupation, represents an anthropogenically induced negative tendency and is dated chemostratigraphically to 1776 ± 46, using a datum related to the onset of local Roman lead mining AD 43-49. Sedimentation rates of the marine clay are established: 1.58-1.92 mm yr-1 and 0.8-0.96 mm yr-1 at sites of maximum and less severe compaction respectively. RSL continued to rise throughout the deposition of the clay unit at a rate of 0.41-0.82 mm yr-1, a view that disagrees with previous models that imply stabilised RSL by 3000 BP. These earlier studies underestimate compaction with implications for subsequent studies employing these sea-level data, particularly in crustal studies where the apparent trend of subsidence is overestimated/increased.

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Two perched dune systems are investigated in the Baie d'Audierne (Finistère, Brittany, northwest France). A maximum age of 4545–4160 cal. yr bp for the onset of sand accretion is provided through radiocarbon (14C) analysis of an organic‐rich basal palaeosol, corresponding closely to deceleration, but before stabilisation, of regional Holocene relative sea levels (RSLs). Molluscan analysis through the dune sand indicates an initial bare sand or sparsely vegetated surface, subsequently maturing and colonised by scrub vegetation, and finally returning to more open dune grassland conditions. These data suggest a three‐stage Perched Dune Development Model (PDDM), which may be applicable to perched dunes on at least a regional scale: (1) initial sand sheet inundation as RSL rises; (2) stabilisation of RSL allowing dune to mature; and (3) sea‐level stabilisation stimulates cliff formation, perching and progressive landward retreat of the dune shore. This study recognises that perched dunes hold greater potential for establishing chronologies for regional Holocene dune development than the more widely studied lowland dune systems, where evidence for early sand inundation may be obscured or lost by modest rises in sea level.