Hostname: page-component-cd9895bd7-fscjk Total loading time: 0 Render date: 2024-12-30T23:19:55.621Z Has data issue: false hasContentIssue false
  • English
  • Français

Clast assembling, bed-forms and structure in gravel beaches

Published online by Cambridge University Press:  03 November 2011

B. J. Bluck
B. J. Bluck
Affiliation:
Department of Geography and Topographic Science, University of Glasgow, Glasgow, G12 8QQ, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Both textural maturity and structure acquired by gravels on beaches are largely a response to the interaction between beach surface and wave-backwash energy. The turbulent energy driving the processes of particle rejection andselection at the surface of growing gravel sheets is partly controlled by the grain size of the sheet itself, so the process is to a large extent self-regulating. Beach surfaces are seen to comprise many discrete sheets of gravel competing for growth at their boundaries, but each characterised by a uniform or uniformly gradational texture.

There are two main types of gravel sheet: (1) selection pavements which occur on low beach slopes, showing little areal grain-size or grain-shape variation, and (2) turbulence shadows which occur on steeper slopes and produce assemblages of clasts which may show perfect lateral shape and size gradation.

The clasts which make up these various gravel sheets are termed ‘clast assemblages’, and such assemblages are the fundamental units from which beaches are constructed. Clast assemblages are classified in terms of their textural maturity—the degree to which they exhibit uniformity in clast size and shape. In beach sections they are, either singly or in combination, bounded by planes of discontinuity (bedding planes) to form beds.

Repeated combinations of either clast assemblages or beds in a genetic association are regarded as sedimentary structures, many of which are diagnostic of the gravel beach environment. Growth of beaches involves the stacking of sedimentary structures, and four growth patterns have been identified. The beach structure is, therefore, classified in a hierarchy comprising clast assemblage, bed, structures and growth form, and it is the growth pattern which may be related to tidal range. P.ecognition of the processes which generate beach gravels through the structure of the gravels permits an analysis of the internal structure of major gravel bodies such as barrier beaches. It adds another set of criteria which may further lead to an understanding of the processes responsible for the generation and evolution of these large gravelforms.

Three types of gravel lithosomes have been identified. (1) Regressive barrier bars which form a series of gravel ridges separated by lagoonal deposits. Barriers are built initially by swash bars which grow in size and coarsen through time to become wave-resistant forms. They form as a response to times when the sediment, unable to be evenly distributed and sorted on the beach surface, forms a discrete bar seaward of the active beach. This is the result of a punctuated or continuously high sediment supply compared with the wave energy available to disperse the sediment, or a falling sea level which shifts the locus of sediment accretion. (2) In contrast, regressive (prograding) gravel sheets form as a response to a continuous supply of sediment to the beach surface, allowing it to build seaward by the uniform accretion of sediment which is sorted and retained on its surface. (3) Gravel sheets produced in transgression are characterised by an abundance of spherical clasts and are often overlapped by the sand beaches which occur seaward of them.

Keywords

barrier beachesbermscuspsgrain assemblageslithosomesregressionselection pavementstidal rangetransgression
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 89 , Issue 4 , 1998 , pp. 291 - 323
Copyright
Copyright © Royal Society of Edinburgh 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Baird, A. J. & Horn, D. P. 1996. Monitoring & modelling groundwater behavior in sandy beaches. Journal of Coastal Research 12, 630–40.Google Scholar
Bluck, B. J. 1967. Sedimentation of beach gravels examples from South Wales. Journal of Sedimentary Petrology 37, 128–56.Google Scholar
Bluck, B. J. 1982. Texture of gravel bars in braided streams. In Hey, R. D., Bathurst, J. C. & Thorn, C. R. (eds) Gravelbed rivers fluvial processes, engineering and management, 339–55. Chichester: John Wiley.Google Scholar
Bluck, B. J. 1987. Bed forms and clast size changes in gravel bed rivers. In Richards, K. (ed.) River channels environment and process, 159–78. Oxford: Blackwell.Google Scholar
Caldwell, N. E. & Williams, A. T. 1985. The role of beach profile configuration in the discrimination between differing depositional environments affecting coarse clastic beaches. Journal of Coastal Research 1, 129–39.Google Scholar
Carr, A. P. 1971. Experiments on longshore transport and sorting of pebbles. Journal of Sedimentary Petrology 41, 1081–104.Google Scholar
Carter, R. W. G. & Orford, J. D. 1980. Gravel barrier genesis and management: a contrast. Coastal Zone '80. Proceedings of 2nd Symposium on Ocean Management. American Society of Civil Engineers 1, 934–48.Google Scholar
Carter, R. W. G. & Orford, J. D. 1988. Conceptual models of coarse clastic barrier formation from multiple sediment sources. Geographical Review 78, 221–39.CrossRefGoogle Scholar
Comber, D. P. M. 1995. Culbin sands and the bar. Scottish Geographical Magazine 111, 54–7.CrossRefGoogle Scholar
Davies, J. L. 1964. A morphogenetic approach to world shorelines. Zeitschrift fiir Geomorphologie 8, 127–94.CrossRefGoogle Scholar
de Decker, R. H. 1988. The wave regime on the inner shelf south of the Orange River and its implications for sediment transport. South African Journal of Geology 19, 358–71.Google Scholar
Devoy, R. J. N., Delany, C, Carter, R. W. G. & Jennings, S. C. 1996. Coastal stratigraphies as indicators of environmental change upon European Atlantic coasts in the late Holocene. Journal of Coastal Research 12, 564–88.Google Scholar
Dobkins, J. E. & Folk, R. L. 1970. Shape development on Tahiti-Nui. Journal of Sedimentary Petrology 40, 116–203.Google Scholar
Everts, C. H. 1973. Particle overpassing on flat granular boundaries. Journal of the Waterways andHarbour Coastal Engineers Division ASCE WW4 425–38.CrossRefGoogle Scholar
Forbes, D. L., Taylor, R. B., Orford, J. D., Carter, R. W. G. & Shaw, J.1991. Gravel barrier migration and overstepping. Marine Geology 97, 305–15.CrossRefGoogle Scholar
Forbes, D. L., Orford, J. D., Carter, R. W. G., Shaw, J. & Jennings, S. G. 1995. Morphodynamic evolution, self organisation and instability of coarse clastic barriers on paraglacialcoasts. Marine Geology 126, 63–85.CrossRefGoogle Scholar
Greensmith, J. T. & Gutmanis, J. C. 1990. Aspects of rate of Holocene depositional history of the Dungeness area, Kent. Proceedings of the Geologists Association 101, 225–37.CrossRefGoogle Scholar
Hart, B. S. & Plint, A. G. 1989. Gravelly shoreface deposits: a comparison of modern and ancient facies sequences. Sedimentology 36, 551–7.CrossRefGoogle Scholar
Hobday, D. K. & Banks, N. L. 1971. A coarse grained pocket beach complex, Tanafjord (Norway). Sedimentology 16, 129–34.CrossRefGoogle Scholar
Hofmann, H. J. 1994. Grain-shape indices and isometric graphs. Journal of Sedimentary Research A 64, 916–20.CrossRefGoogle Scholar
Howard, J. L. 1992. An evaluation of shape indices as palaeoenvironmental indicators using quartzites and metavolcanic clasts in Upper Cretaceous to Palaeogene beach, river and submarine fan conglomerates. Sedimentology 39, 471–86.CrossRefGoogle Scholar
Humbert, F. L. 1968. Selection and wear of pebbles on a gravel beach. Geological Institute Groningen 190.Google Scholar
Illenberger, W. K. 1991. Pebble shape (and size) Journal of Sedimentary Petrology 61, 756–67.Google Scholar
Illenberger, W. K., Reddering, J. S. V. & Howard, J. L. 1993. A discussion of‘An evaluation of shape indices as palaeoenvironmental indicators using quartzites and metavolcanic clasts in Upper Cretaceous to Palaeogene beach, river and submarine fan conglomerates’. Sedimentology 40, 1019–21.CrossRefGoogle Scholar
Isla, F. J. 1993. Overpassing and armouring phenomena on gravel beaches. Marine Geology 110, 369–76.CrossRefGoogle Scholar
Jennings, S. C. & Smyth, C. 1990. Holocene evolution of the gravel coastline of East Sussex. Proceedings of the Geologists Association 101, 204–24.CrossRefGoogle Scholar
Leckie, D. A. & Walker, R. G. 1982. Storm- and tide-dominated shorelines in Cretaceous Mosebar-Lower Gates interval-outcrop equivalents of Deep Basin gas trap in western Canada. Bulletin of the American Association of Petroleum Geologists 66, 138–57.Google Scholar
Long, A. J. & Hughes, P. D. M. 1995. Mid- and Late Holocene evolution of Dungeness foreland. U.K. Marine Geology 124, 253–71.CrossRefGoogle Scholar
Maejima, W. 1982. Texture and stratification of gravelly beach sediments, Enju Beach, Kii Peninsular, Japan. Journal of Geoscience, Osaka University 25, 35–51.Google Scholar
Massari, F. & Parea, G. C. 1988. Progradational gravel beach sequences in a moderate-to-high energy, microtidal marine environment. Sedimentology 35, 881–913.CrossRefGoogle Scholar
Moss, A. J. 1962. The physical nature of common sandy and pebbly deposits 1. American Journal of Science 260, 337–73.CrossRefGoogle Scholar
Moss, A. J. 1963. The physical nature of common sandy and pebbly deposits 2. American Journal of Science 261, 297–43.CrossRefGoogle Scholar
Neilson, H. L., Johannesen, P. N. & Surlyk, F. 1988. A late Pleistocene coarse-grained spit-platform sequence in northern Jylland, Denmark. Sedimentology 35, 915–37.Google Scholar
Orford, J. D. 1975. Discrimination of particle zonation on a pebble beach. Sedimentology 22, 441–63.CrossRefGoogle Scholar
Orford, J. D. 1977. A proposed mechanism for beach sedimentation. Earth Surface Processesand Landforms 2, 381–400.CrossRefGoogle Scholar
Orford, J. D. & Carter, R. W. G. 1982. Crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast, Carnsore Point, Southeast Ireland. Journal of Sedimentary Petrology 52, 265–78.Google Scholar
Orford, J. D., Carter, R. W. G. & Jennings, S. C. 1991a. Coarse clastic barrier environments: evolution and implicationsfor Quaternary sea level interpretation. Quaternary International 9, 87–104.CrossRefGoogle Scholar
Orford, J. D., Carter, R. W. G. & Forbes, D. L. 1991b. Gravel barrier migration and sea level rise: some observations from Stony Head, Nova Scotia, Canada. Journal of Coastal Research 7, 477–88.Google Scholar
Orford, J. D., Carter, R. W. G., Jennings, S. C. & Hinton, A. C. 1995a. Processes and timescales by which a coastal gravel dominated barrier responds geomorphologically to sea-level rise: Stroy Head Barrier, Nova Scotia. Earth Surface Processes and Landforms 20, 21–37.CrossRefGoogle Scholar
Orford, J. D., Carter, R. W. G., McKenna, J. & Jennings, S. C. 1995b. The relationship between meso-scale sea level riseand the rate of retreat of swash-gravel dominated barriers. Marine Geology 124, 177–86.CrossRefGoogle Scholar
Orford, J. D., Carter, R. W. G. & Jennings, S. C. 1996. Control domains and morphological phases in gravel dominated coast barriers of Nova Scotia. Journal of Coastal Research 12, 589–604.Google Scholar
Postma, G. & Nemec, W. 1990. Regressive and trangressive sequences in a raised Holocene gravelly beach, southwestern Crete. Sedimentology 37, 907–20.CrossRefGoogle Scholar
Rosen, P. & Leach, K. 1987. Sediment accumulation forms, Thompson Island, Boston Harbour, Massachusetts. In Fitzgerarld, D. & Rosen, P. (eds) Glaciated coasts, 234–51. San Diego: Academic Press.Google Scholar
Sherman, D. J. 1991. Gravel beaches. Natural Geographic Research Exploration 7, 442–52.Google Scholar
Sherman, D. J., Orford, J. D. & Carter, R. W. G. 1993. Development of cusp-related, gravel size and shape facies at Malin Head, Ireland. Sedimentology 40, 1139–52.CrossRefGoogle Scholar
Sneed, E. D. & Folk, R. L. 1958. Pebbles in the lower Colorado River, Texas–a study in particle morphogenesis. Journal of Geology 66, 114–50.CrossRefGoogle Scholar
Steers, J. A. 1937. The Culbin Sands and Burghhead bay. Geographical Journal 90, 498–528.CrossRefGoogle Scholar
Williams, A. T. & Caldwell, N. E. 1988. Particle size and shape in pebble beach sedimentation. Marine Geology 82, 199–215.CrossRefGoogle Scholar
Zingg, T. 1935. Beitrag zur schotteranalyse. Schweizerische Mineralogische und Petrographische Mitterlugen 15, 39–140.Google Scholar