Evolution of estuarine facies in a tidal channel environment, SW Spain: evidence for a change from tide- to wave-domination

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The transition from tide- to wave-dominated environments is documented in Holocene estuaries along the mesotidal coast of Huelva, southwestern Spain. This transition is a consequence of the decreasing tidal prism caused by estuarine siltation, a process favoured by the inherited morphology of the prior fluvial valleys. The Domingo-Rubio tidal channel is a small estuary adjacent to the mouth of two wave-dominated estuaries along the coast of Huelva. Coring and vibracoring of both surficial and subsurface sediments allow the distinction of six lithofacies that form five depositional environments: (1) salt marsh; (2) active channel-margin; (3) washover-fan; (4) tidal channel; and (5) estuarine channel. The facies architecture reveals the infilling process of the tidal channel due to the interaction of both waves and tides. Wave activity is registered in the elongation of the spit, whereas tidal action produces facies associations characteristic of tide-dominated estuaries. The recent history of this estuary records three successive stages: (1) an initial tide-dominated open marine environment; beginning at 3090 ± 60 years B.P., with strong tidal currents in very energetic channels displaying a straight-meandering-straight morphology; (2) a wave-dominated period during which waves transport sand into the inner estuary and also along the mouth spit at about 2500 years B.P.; and (3) a second tide-dominated stage from 300 ± 80 years B.P. onward, during which weaker tidal currents distribute the sediment. Four factors controlled the transition from tide to wave domination: (1) the relief formed during deposition; (2) the decreasing tidal prism; (3) the inner facies distribution versus those of the outlet; and (4) the seaward spit elongation of adjacent estuaries.