DIFFERENTIAL PRESERVATION OF COASTAL STRUCTURES ON PARAGLACIAL SHELVES - HOLOCENE DEPOSITS OF SOUTHEASTERN CANADA

Recent work has advanced our understanding of mixed sand-gravel littor al systems in glaciated regions. New insights include the nature and c auses of coastal instability and conditions for preservation of Holoce ne barrier deposits on paraglacial shelves. The best-preserved relict barrier structures recognized on the inner shelf of southeastern Canad a are interpreted as postglacial lowstand deposits, initiated under st able to slowly rising relative sea level in areas of substantial shelf relief. A largely intact early-Holocene gravel foreland survives at 3 8 m present water depth, its preservation attributed in part to sedime nt volume and a partially protected location. The mechanism by which t his structure was abandoned and overstepped is unclear, but may be rel ated to accelerating sea-level rise. In some cases, barriers keep pace with sea-level rise for some time before being overstepped or reworke d landward. The duration and extent of preservation depend in part on the deposit volume, as smaller accumulations are consumed and reworked more quickly. Deposit volume is a function of sediment supply, accomm odation space, and headland spacing, among other factors. Where barrie rs are small and thin, beach sediments, overtaken by the transgression , may be smeared across the shoreface in a thin post-transgressive ven eer. In such settings, as along the Eastern Shore of Nova Scotia, the only coastal units preserved on the shelf are back-barrier estuarine f acies in flooded-valley depressions. Differential preservation is gove rned by shelf relief and accommodation space, coastal alignment and co mpartmentalisation, sediment supply and barrier volume, rate and accel eration of sea-level rise, wave energy and potential for sediment rewo rking on the inner shelf.