IMPLICATIONS FOR SEA-LEVEL RESEARCH OF SALT-MARSH AND MUDFLAT ACCRETIONARY PROCESSES ALONG PARAGLACIAL BARRIER COASTS

Paraglacial coastlines with dynamic, coarse elastic barrier beaches ar e common in mid- to high-latitudes today, and have been during the Hol ocene. Sediments that have been deposited along these coastlines, ofte n in back-barrier locations, have been used to reconstruct relative se a-level (RSL) movements and tendencies, usually through the use of sea -level index points, derived frequently from salt marsh and mudflat de posits. However, the asymptotic relationship between minerogenic marsh /mudflat accretion rates and time will produce regressive stratigraphi es with a negative sea-level tendency signature, even within regimes o f rising RSL. The influence of gravel barriers on sedimentation will a lso tend to encourage regressive stratigraphies. Furthermore, organoge nic sediment production may release marsh accretion rates from the con trol of tidal inundation and result in succession to reed swamp despit e RSL rise. Episodic minerogenic sediment supply to the marsh can trig ger switches between marsh emergence and submergence, which may result in stratigraphic sequences corresponding to negative and positive ten dencies of RSL respectively, although submergence may be prevented by organogenic sediment supply. Forcing by RSL rise may result in marsh e mergence following initial submergence, as a result of renewed accreti on on the submerged marsh.