Beach ridges - definitions and significance

Beach ridges, frequent components of Quaternary coastal plains, and other coastal landforms, have been cited as indicators of the positions of ancient seashores and associated sea levels. Numerous authors utilized the term bench ridge for active and relict, usually wave-built supratidal and/or intertidal forms. Wind-built ridges have been only occasionally included in the definition. The term was applied also to submerged, landward-shifting, eventually stranded bars. A consistent redefinition of the term is highly desirable. Bench ridges should include all relief strandplain ridges, whether dominated by wave/swash-built or by eolian lithosomes. All active ridge-like shore features, regardless of dimensions, morphology, and origin are excluded. Because of the resistance of coarse-elastic ridges to wave and wind erosion, swash-built gravel or coarse shell ("storm") ridges may build several meters above the level of high tide. Swash-built high berms, even on pure sandy beaches, exceed the highest tides during episodes of wind-induced, record water levels. Frequently but not always burying underlying low-relief "berm ridges" of berm lithosomes, sequences of relatively steep multiple foredunes are commonly named bench ridge plains. The narrow, subparallel relict foredunes that form these strandplains presently are designated as eolian bench ridges. Beach ridges, thus, are defined as relict, semiparallel, multiple wave- and wind-built landforms that originated in the inter- and supratidal zones. Until separated from the shoreline by progradation, sandy, pebbly or shell-enriched backshore berm ridges behind an active foreshore should not be considered beach ridges. Strandplain progradation is either continuous or, with the inclusion of subtidal ("cat's eye'') ponds, discontinuous. Contrary to claims, transgressive cheniers do not represent "true cheniers" alone; within their overall progradational context, cheniers, a special category of beach ridges bracketed by subtidal-intertidal mudflats, may be transgressive or regressive in character. Landward-driven, transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats. When recognizable between clearly identifiable intertidal and overlying eolian intervals, the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide/lake levels. Diagnostic sedimentary textures, structures, and fossils, however, often may be unavailable in the deposits. Along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide, beach ridges of clearly proven wave-built origin may also serve as indicators of ancient higher-than-present sea levels. (C) 2000 Elsevier Science B.V. All rights reserved.