Page 222 - Sedimentology and Stratigraphy

Estuaries 209

Fig. 13.13 Distribution of depositional settings in a wave-dominated estuary.

Fig. 13.14 A wave-dominated estuary, with an extensive beach barrier protecting a lagoonal area.
deposited. The form and processes of a bay-head delta at the barrier bar. The central lagoon is therefore a
will be those of a river-dominated delta (12.4.5) region of fine-grained deposition, often rich in organic
because the tidal effect is minimal and the barrier material, similar to normal lagoonal conditions
protects the central lagoon from strong wave energy. (13.3.2). When the central lagoon becomes filled
A coarsening-up, progradational succession will be with sediment it becomes a region of salt-water
formed, with channel and overbank facies building marshes crossed by channels. In wave-dominated
out over sands deposited at the channel mouth, estuaries, parts of the lagoon that receive influxes of
which in turn overlies fine-grained deposits of the sand may be areas where wave-ripples form and these
central lagoon. may also be draped with mud.

Central lagoon Beach barrier
The lowest energy part of the estuarine system is the The outer part of a wave-dominated estuary is a zone
central lagoon, where the river flow rapidly de- where wave action reworks marine sediment (bio-
creases and the wave energy is mainly concentrated clastic material and other sediment reworked by