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

Paraglacial coastlines with dynamic, coarse elastic barrier beaches are common in mid- to high-latitudes today, and have been during the Holocene. Sediments that have been deposited along these coastlines, often in back-barrier locations, have been used to reconstruct relative sea-level (RSL) movements and tendencies, usually through the use of sea-level index points, derived frequently from salt marsh and mudflat deposits. However, the asymptotic relationship between minerogenic marsh/mudflat accretion rates and time will produce regressive stratigraphies with a negative sea-level tendency signature, even within regimes of rising RSL. The influence of gravel barriers on sedimentation will also tend to encourage regressive stratigraphies. Furthermore, organogenic sediment production may release marsh accretion rates from the control of tidal inundation and result in succession to reed swamp despite RSL rise. Episodic minerogenic sediment supply to the marsh can trigger switches between marsh emergence and submergence, which may result in stratigraphic sequences corresponding to negative and positive tendencies of RSL respectively, although submergence may be prevented by organogenic sediment supply. Forcing by RSL rise may result in marsh emergence following initial submergence, as a result of renewed accretion on the submerged marsh.