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TitleMorphodynamic evolution, self-organisation, and instability of coarse-clastic barriers on paraglacial coasts
AuthorForbes, D L; Orford, J D; Carter, R W G; Shaw, J; Jennings, S C
SourceMarine Geology vol 126, 1995 p. 63-85,
Alt SeriesGeological Survey of Canada, Contribution Series 37894
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceEastern offshore region; Nova Scotia
AreaHalifax; Eastern Shore
Lat/Long WENS -63.2500 -63.0000 44.7500 44.5833
Subjectsmarine geology; sedimentology; surficial geology/geomorphology; coastal environment; coastal studies; postglacial evolution; beaches; tidal barriers; glacial deposits; glacial history; morphology; gravels; sedimentation; sea level changes; sands; paraglacial coasts; Quaternary
Illustrationssketch maps; graphs; plots
AbstractBeaches and barriers on many mid- to high-latitude coasts comprise mixtures of fine and coarse clastic materials forming a distinctive morphodynamic environment. In many cases, the sediments are derived primarily from limited glacigenic deposits and the coasts are considered paraglacial. Over relatively long time scales (decades to centuries), coarse-clastic barriers on such coasts show evidence of self-organisation through large-scale morphological evolution and facies differentiation. This process involves gradual reworking, partitioning, and textural sorting of material toward transport minima. Long intervals of slow evolution are punctuated by episodes of rapid reorganisation, involving breakdown of stable barrier structures and facies patterns, remixing of sediment, and accelerated migration of transgressive systems. Drift-aligned systems develop longshore cell structure, sometimes leading to breaching and segmentation, and may evolve toward progressively greater swash alignment under appropriate circumstances. Swash-aligned systems may experience catastrophic transformation when appropriate environmental triggers lead to threshold exceedance in the morphodynamics of the shore system. Adjacent barriers may show quite different behaviour, depending on the antecedent states of individual coastal cells. While appropriate parameterisations and sediment budget formulations allow us to model the long-term evolution of some barrier structures, the non-linear dynamics that appear to dominate large-scale behaviour may limit predictability. The identification of stability threshold criteria remains an important research priority.