Sedimentary Environment

Where the land meets the sea, interplay between terrestrial and marine processes causes sedimentary environments to be very complex. In areas where wave energy is low and the tidal range (the difference between high tide and low tide) is also low, terrestrial processes usually dominate. For example, sediments flowing into the sea from a river will form a well-developed delta. If wave energy is high and tidal range low, the river's sediments will be reworked into a beach or barrier island. However, if tidal range is high, tidal currents flood the river mouth daily, forming a drowned river mouth, or estuary, with scattered sand bars.

In coastal areas remote from rivers, the nature of the coast changes rapidly. The balance between tidal and wave processes influences coastal character. The higher the tidal range, the more important tidal processes become. In wave-dominated areas, currents flowing parallel to the shoreline move sand along the coast, producing barrier islands and beaches for long stretches. If a barrier island protects the coast, channels, or tidal inlets, pass between the islands and allow tidal currents to flow from the open ocean into the bay behind the island. Landward from the bay, a tidal marsh will occur. When high tide approaches and tidal currents flow landward, the marsh will be flooded. As the water level drops toward low tide, tidal currents flow seaward, exposing the marsh to the elements. If no barrier island is present, coasts are rather simple with only occasional river mouths and coastal marshes to break the monotony of long stretches of beach.

Where tidal range is high, strong tidal currents dominate coastal processes. Tidal sand flats occur below low tide level. These are generally covered with large ripples to small sand dunes. Between the low tide and high tide marks, ripples are abundant on a mixed sand and mud flat. A mud flat, backed by a tidal marsh, forms above the high tide mark. Landward of the low tide level, tidal creeks cut through the deposits as well.