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570 SEDIMENTARY ENVIRONMENTS/Shoreline and Shoreface Deposits Sedimentology and Paleontology, Tulsa: Society of Economic Paleontologists and Mineralogists Sellwood BW (1986) Shallow marine carbonate envir onments In: Reading HG (ed.) Sedimentary Environ ments and Facies, pp 283 342 Oxford: Blackwell Scientific Wood R (1999) Reef Evolution Oxford: Oxford University Press Wright VP and Burchette TP (1996) Shallow water carbon ate environments In: Reading HG (ed.) Sedimentary Environments: Processes, Facies and Stratigraphy, pp 325 394 Blackwell Science Shoreline and Shoreface Deposits J Howell, University of Bergen, Bergen, Norway ß 2005, Elsevier Ltd All Rights Reserved Introduction A shoreline is the interface between a standing body of water, typically the sea, and a landmass Over geological time, shorelines are highly transient features and the depositional and erosional systems associated with them are extremely dynamic The shoreface sensu stricto is defined as the zone that lies between the low tidemark and the fair weather wave base (the maximum depth at which everyday wave movements affect the seabed) The shoreface is part of a linked depositional system that includes all of the coastal region affected by wave action, from the top of the beach, seaward, to the mean storm wave base (the maximum typical depth at which the storm waves move sediment on the seafloor) (see Sedimentary Environments: Storms and Storm Deposits) At the shoreline, wave processes are the most significant agents of erosion, sediment transport, and deposition, although fluvial, tidal, and biogenic processes are also important and may be locally dominant Sediments deposited in the system may be siliciclastic, carbonate, or a mixture of the two, and grain sizes can range from those of clay particles to boulders The position of the shoreline is highly sensitive to changes in sea-level and sediment supply, and understanding shoreline systems is central to sequence stratigraphy and basin analysis Shoreface deposits form important hydrocarbon reservoirs and aquifers in many parts of the world, and some contain placer mineral and gem deposits Modern systems are environmentally sensitive areas and many of the world’s coastlines are heavily populated and susceptible to sea-level change The study of shoreline processes and deposits includes aspects of geology, geomorphology, biology, and oceanography Both physical and biogenic processes (see Sedimentary Environments: Carbonate Shorelines and Shelves) occur at shoreline systems All clastic, coastal depositional systems can be classified within a triangular diagram that summarizes the relative importance of fluvial, tidal, and wave processes (Figure 1A) Away from fluvial input points, the key controlling factor is the tidal range In areas with a moderate to low tidal range, narrow beaches dominated by wave action occur Conversely, in areas with a high tidal range, broad low-lying, muddy tidal flats are created (Figure 1B) The wave-dominated, beach-related systems that make up the majority of the world’s coastlines are the focus here (but see Sedimentary Processes: Fluvial Geomorphology) Wave Processes Surface water waves are formed by the movement of the wind across a standing body of water Wind shear effectively drags the upper layers of the water and horizontally compresses them, producing waves The key features of a wave are its length and height (Figure 2) Within the water body, the vertical motion at the water surface sets up circular orbital motion that is translated downward This downward translation of energy typical moves the water in a series of orbital motions to a depth that is approximately half of the wave length This depth is termed the ‘wave base’ (Figure 2), and waves that occur in water that is deeper than the wave base will not move sediment on the seafloor Because the depth to the wave base is controlled by the size of a wave, it varies both between basins and over time within an individual basin In large, open bodies of water with a large fetch (such as the major oceans), the wave base may be in excess of 100 m, whereas in enclosed seas and lakes, it may be less than 10 m Wave size and the depth to the wave base also vary within an individual setting on a daily and seasonal basis, depending on changes in the weather During storms, short-term, larger waves result in a deep wave base, whereas during fair weather periods, the wave base is much shallower It is common to consider marine depositional systems in terms of two hypothetical surfaces,
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