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Coastal geomorphology
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Cuspate forelands, such as Cape Canaveral, Florida, and Dungeness, in southern England, are accumulations of coastal debris of triangular form, contrasting with that of spits. They were originally thought to be due either to the junction of two large opposed coastal eddies or to wavefront convergence caused by a submerged offshore obstruction. Detailed work on Dungeness by Lewis (1932), however, suggests that their development may be closely allied to that of spits and that changes of sea level, sources of debris supply and wave directions may be important. In Roman times when sea level was some 1.7 m lower than at present, the present area of Romney Marsh was probably a shallow cliff-fringed bay, perhaps more or less isolated from the open sea by a spit (Figure 15.19). It is possible that the following rise of sea level increased the longshore debris supply from the southwest which led to the building of a series of spits (AB, AC, AE, AFG). This phase may have been terminated by a breach in the spit at the southern end near Fairlight, which cut off the debris supply and caused the spit to realign at right angles to the dominant south-south-west swell waves and to retreat northward (HK, MP, BP). As the spit built eastward into deeper water it came under the action of infrequent east-north-easterly storm waves from upchannel and recurved (PNO, PQR), and at the same time the depletion of debris in the north causing erosion between New Romney and Hythe, which was checked in 1803–4 by the building of the Dymchurch Wall. The northward movement of the southerly spit-front was succeeded after 1538 by the building of a prograded sequence of smaller spits to the east of Camber Castle, which was constructed in that year on the then coastline.
Geoheritage significance of three Pleistocene formations recording a succession of climates and sea levels on the Yalgorup Plain in southwestern Australia
Published in Australian Journal of Earth Sciences, 2019
The key to understanding ancient sequences is finding modern sequences that can act as dynamic analogues in which to explore relationships between lithofacies or biofacies and various environmental parameters, such as wind, temperature and, and wave intensity. The Tims Thicket Limestone and Kooallup Limestone, which formed during Pleistocene cuspate foreland development on the Yalgorup Plain (V. Semeniuk, 1997), have direct modern examples along the southwestern Australian coast. We selected the Rockingham–Becher Plain (Searle et al., 1988; V. Semeniuk et al., 1988) as its modern equivalent. It is the best modern analogue for both limestone formations, because of its comparable geographic setting, and its development of similar sedimentary units. Within a typical cuspate foreland, a shoaling sequence is recorded, comprising seagrass banks, capped by beach- and dune-derived units. The seagrass unit, characterised by bioturbation, high carbonate content and a distinct fossil assemblage has proven to be the most useful unit for paleo-environmental interpretation of these formations. The seagrass unit comprises mollusc and foraminiferal species known to live on modern-day seagrass leaves, e.g., the diagnostic mollusc genera Bulla, Olivia, Phasinella and Parcanassa. As such, the biofacies of these limestones provide a modern analogue for determining sea level, as well as water temperature, as a simple proxy for climate.