Tidal Flats and Subtidal Sand Bodies

In recent years the ichnology of tide-dominated and influenced environments has mainly been focused on marginal-marine brackish-water environments, such as estuaries and bays, rather than open-marine tide-dominated settings. This chapter reviews ichnofaunas developed in macrotidal open-marine tidal flats and subtidal sand bodies and their relationship to sedimentary processes and environmental controls. The intertidal zone represents an extremely harsh ecosystem in which benthic organisms are mostly controlled by the interplay of salinity, sediment mobility and hydrodynamic energy, time of exposure to subaerial conditions, temperature, substrate type and food supply. Benthic faunas in tide-dominated subtidal sand bodies (i.e. compound dune fields, sand sheets, sand ridges, isolated dune patches, Ridal bars) are mostly controlled by the interplay of salinity, sediment mobility and hydrodynamic energy, water turbidity, substrate type and food supply. The ichnofacies gradient across tide-dominated shorelines is to some extent opposite to that observed in wave-dominated environments. Near the shoreline, the overall tidal energy increases from the supratidal to the shallow subtidal. Whereas the Skolithos Ichnofacies tends to dominate lower intertidal and shallow subtidal deposits, the Cruziana Ichnofacies is best developed in middle and upper intertidal environments, as well as in low-energy areas of the inner shelf.