Evolutionary Classification of Coastal Sediments

ABSTRACT One of the most successful ways of classifying coastal environments has been to employ the dominant coastal process variables as discriminating parameters. This approach has been previously applied to deltas and continental shelves using the three parameters of waves, tides and rivers and to tidal inlets using only waves and tides. We suggest that a three parameter triangular classification can be extended to all coastal environments and enables a division into the primary categories of deltas, estuaries, barriers and tidal flats. Although combinations of coastal processes may remain constant through time on any coast, the coast itself undergoes continuous evolution. This necessitates the inclusion of time as a fourth parameter to satisfy an evolutionary coastal classification. If we adopt a sequence stratigraphic view of coastal evolution, then we may place most coastal sediments within either the transgressive or highstand systems tracts, undergoing either progradation (regression) or flooding (transgression). If we assume that all temporal evolution between sedimentary environments within the coastal system takes place during either a regression or transgression then we can substitute regression/transgression for time as the fourth parameter. Using this approach we see that all environments may occur in the general case but that at times of (maximum) flooding, estuaries predominate and that as sediment continues to be supplied during progradation, deltas, barriers and tidal flats expand at the expense of estuaries. At any one time, each depositional environment may be further subdivided using wave, tide and river process domination.